[PATCH 0/4] make: precompile "git-compat-util.h"

[PATCH 0/4] make: precompile "git-compat-util.h"

[SZEDER Gábor]

Update our Makefile to make use of the recently introduced precompiled
header to make builds faster (on my setup by about 35%).


SZEDER Gábor (4):
  Makefile: remove XDIFF_OBJS initialization
  cmake: remove any "$(*_OBJS)" variables when parsing Makefile for
    sources
  Makefile: reintroduce REFTABLE_OBJS
  Makefile: precompile "git-compat-util.h"

 .gitignore                          |  1 +
 Makefile                            | 59 +++++++++++++++++++----------
 contrib/buildsystems/CMakeLists.txt |  6 ++-
 3 files changed, 45 insertions(+), 21 deletions(-)

-- 
2.55.0.1193.g1b994e35de

[PATCH 1/4] Makefile: remove XDIFF_OBJS initialization

[SZEDER Gábor]

Object files under 'xlib/' used to be listed in the XDIFF_OBJS
Makefile variable so we could build a static library from them.  This
static library was removed in cf680cdb95 (make: delete XDIFF_LIB, add
xdiff to LIB_OBJS, 2025-10-02), along with filling XDIFF_OBJS with
object files.

But the initial empty initalization of XDIFF_OBJS remained, so remove
it now.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
---
 Makefile | 1 -
 1 file changed, 1 deletion(-)

diff --git a/Makefile b/Makefile
index d4b775953d..7d9ac15c74 100644
--- a/Makefile
+++ b/Makefile
@@ -695,7 +695,6 @@ BUILTIN_OBJS =
 BUILT_INS =
 COMPAT_CFLAGS =
 COMPAT_OBJS =
-XDIFF_OBJS =
 GENERATED_H =
 EXTRA_CPPFLAGS =
 FUZZ_OBJS =
-- 
2.55.0.1193.g1b994e35de

[PATCH 2/4] cmake: remove any "$(*_OBJS)" variables when parsing Makefile for sources

[SZEDER Gábor]

To get various lists of files, CMake parses our Makefile looking for
lines matching e.g. "list_var += ...".  In case of LIB_OBJS this
picks up the line "LIB_OBJS += $(COMPAT_OBJS)" as well, so the parsing
macro has a specific instruction to remove "$(COMPAT_OBJS)" from the
resulting list.

Currently this is the only such Makefile variable to be removed from
the list, but the next patches will (re)introduce more variables
containing lists of object files, so let's generalize that removing
instruction to remove any "$(*_OBJS)" Makefile variable as well.

Note that we can't make the pattern matching the Makefile variable too
general, e.g. to match any "$(VARIABLE)", because some lines of our
Makefile do contain variables as directory prefixes, e.g.
"UNIT_TEST_OBJS += $(UNIT_TEST_DIR)/test-lib.o", and we must
definitely keep those.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
---

I rarely do CMake, so it's quite possible that this is not the most
straightforward or idiomatic approach.

 contrib/buildsystems/CMakeLists.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/contrib/buildsystems/CMakeLists.txt b/contrib/buildsystems/CMakeLists.txt
index 8f56203f34..241da0d43a 100644
--- a/contrib/buildsystems/CMakeLists.txt
+++ b/contrib/buildsystems/CMakeLists.txt
@@ -102,7 +102,7 @@ project(git
 macro(parse_makefile_for_sources list_var makefile regex)
 	file(STRINGS ${makefile} ${list_var} REGEX "^${regex} \\+=(.*)")
 	string(REPLACE "${regex} +=" "" ${list_var} ${${list_var}})
-	string(REPLACE "$(COMPAT_OBJS)" "" ${list_var} ${${list_var}}) #remove "$(COMPAT_OBJS)" This is only for libgit.
+	string(REGEX REPLACE "\\$\\([^)]*_OBJS\\)" "" ${list_var} ${${list_var}}) # remove any "$(*_OBJS)" variables
 	string(STRIP ${${list_var}} ${list_var}) #remove trailing/leading whitespaces
 	string(REPLACE ".o" ".c;" ${list_var} ${${list_var}}) #change .o to .c, ; is for converting the string into a list
 	list(TRANSFORM ${list_var} STRIP) #remove trailing/leading whitespaces for each element in list
-- 
2.55.0.1193.g1b994e35de

[PATCH 3/4] Makefile: reintroduce REFTABLE_OBJS

[SZEDER Gábor]

Object files under "reftable/" used to be listed in the REFTABLE_OBJS
Makefile variable so we could build a static library from them.  This
static library was removed in f3b4c89d59 (make: delete REFTABLE_LIB,
add reftable to LIB_OBJS, 2025-10-02), along with filling
REFTALBE_OBJS with object files.

However, the reftable source files are kind of special, because the
reftable implementation is supposed to be easily includable in other
projects.  Therefore, the reftable source files don't include
"git-compat-util.h", with the sole exception of the purposefully
project-specific "reftable/system.c".  Consequently, they shouldn't be
compiled with our precompiled header, as it does include
"git-compat-util.h".

Resurrect listing object files under "reftable/" in REFTABLE_OBJS (but
not the static library), so in the next commit we'll be able to easily
filter them out and keep building them the old way, without the
precompiled header.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
---
 Makefile                            | 32 ++++++++++++++++-------------
 contrib/buildsystems/CMakeLists.txt |  4 ++++
 2 files changed, 22 insertions(+), 14 deletions(-)

diff --git a/Makefile b/Makefile
index 7d9ac15c74..2c4d6f4d4a 100644
--- a/Makefile
+++ b/Makefile
@@ -707,6 +707,7 @@ OBJECTS =
 OTHER_PROGRAMS =
 PROGRAM_OBJS =
 PROGRAMS =
+REFTABLE_OBJS =
 RUST_SOURCES =
 EXCLUDED_PROGRAMS =
 SCRIPT_PERL =
@@ -1284,20 +1285,6 @@ LIB_OBJS += refs/iterator.o
 LIB_OBJS += refs/packed-backend.o
 LIB_OBJS += refs/ref-cache.o
 LIB_OBJS += refspec.o
-LIB_OBJS += reftable/basics.o
-LIB_OBJS += reftable/block.o
-LIB_OBJS += reftable/blocksource.o
-LIB_OBJS += reftable/error.o
-LIB_OBJS += reftable/fsck.o
-LIB_OBJS += reftable/iter.o
-LIB_OBJS += reftable/merged.o
-LIB_OBJS += reftable/pq.o
-LIB_OBJS += reftable/record.o
-LIB_OBJS += reftable/stack.o
-LIB_OBJS += reftable/system.o
-LIB_OBJS += reftable/table.o
-LIB_OBJS += reftable/tree.o
-LIB_OBJS += reftable/writer.o
 LIB_OBJS += remote.o
 LIB_OBJS += repack.o
 LIB_OBJS += repack-cruft.o
@@ -1386,6 +1373,23 @@ LIB_OBJS += xdiff/xpatience.o
 LIB_OBJS += xdiff/xprepare.o
 LIB_OBJS += xdiff/xutils.o
 
+REFTABLE_OBJS += reftable/basics.o
+REFTABLE_OBJS += reftable/block.o
+REFTABLE_OBJS += reftable/blocksource.o
+REFTABLE_OBJS += reftable/error.o
+REFTABLE_OBJS += reftable/fsck.o
+REFTABLE_OBJS += reftable/iter.o
+REFTABLE_OBJS += reftable/merged.o
+REFTABLE_OBJS += reftable/pq.o
+REFTABLE_OBJS += reftable/record.o
+REFTABLE_OBJS += reftable/stack.o
+REFTABLE_OBJS += reftable/system.o
+REFTABLE_OBJS += reftable/table.o
+REFTABLE_OBJS += reftable/tree.o
+REFTABLE_OBJS += reftable/writer.o
+
+LIB_OBJS += $(REFTABLE_OBJS)
+
 BUILTIN_OBJS += builtin/add.o
 BUILTIN_OBJS += builtin/am.o
 BUILTIN_OBJS += builtin/annotate.o
diff --git a/contrib/buildsystems/CMakeLists.txt b/contrib/buildsystems/CMakeLists.txt
index 241da0d43a..462c1eb5ec 100644
--- a/contrib/buildsystems/CMakeLists.txt
+++ b/contrib/buildsystems/CMakeLists.txt
@@ -668,6 +668,10 @@ include_directories(${CMAKE_BINARY_DIR})
 #libgit
 parse_makefile_for_sources(libgit_SOURCES ${CMAKE_SOURCE_DIR}/Makefile "LIB_OBJS")
 
+#reftable
+parse_makefile_for_sources(reftable_SOURCES ${CMAKE_SOURCE_DIR}/Makefile "REFTABLE_OBJS")
+list(APPEND libgit_SOURCES ${reftable_SOURCES})
+
 list(TRANSFORM libgit_SOURCES PREPEND "${CMAKE_SOURCE_DIR}/")
 list(TRANSFORM compat_SOURCES PREPEND "${CMAKE_SOURCE_DIR}/")
 
-- 
2.55.0.1193.g1b994e35de

[PATCH 4/4] Makefile: precompile "git-compat-util.h"

[SZEDER Gábor]

This patch follows the idea of 671df48df8 (meson: precompile
"git-compat-util.h", 2026-03-19) to make it faster to build Git using
"make".  The notable differences are the boilerplate needed to wire up
the precompiled header with "make", and the selection of object files
that are built using the precompiled header:

  - Add a new rule to precompile "tools/precompiled.h" into
    "tools/precompiled.h.gch".

    This rule and its dependencies are basically the same as our
    existing rule and its dependencies for compiling object files from
    our source files and, except that in this rule we don't use the
    EXTRA_CPPFLAGS target-specific variable.  This is partly because
    any compiler flags in that target-specific variable can't possibly
    make sense for the project-wide "git-compat-util.h", and partly
    because it could run afoul of "make"'s quirks with target-specific
    variables and GCC's "-Winvalid-pch" compiler option [1].

    Our Makefile always writes object files next to the source files
    they were compiled from.  Since a precompiled header is in many
    ways similar to an object file, let's follow suit and write it
    next to the header file it was created from as well.  671df48df8
    doesn't mention why "precompiled.h" was placed in "tools/".

    Use the ".gch" suffix for the precompiled header file, because
    that's the only suffix GCC looks for when searching for a
    precompiled header.  Clang apparently looks for both ".pch" and
    ".gch" suffixes.  If we ever encounter a compiler which only
    supports a different precompiled header suffix, then we might make
    the suffix configurable via a Makefile knob; but until then it
    remains hard-coded for the sake of simplicity.

  - Declare the precompiled header's dependencies, so it gets rebuilt
    when any of our header files it includes is modified.

    When using computed header dependencies, then the compiler can
    generate the Makefile snippet containing the header files inlcuded
    by the precompiled header, just like when compiling a C source
    file into an object file.

    When not using computed header dependencies, then make the
    precompiled header depend on the same header files that our object
    files depend on, i.e. those listed in LIB_H and GENERATED_H.  This
    is not ideal, because the precompiled header will be rebuilt even
    when a header file it doesn't actually depend on changes; but in
    that case all object files will be rebuilt as well anyway.

  - List the object files that are built using the precompiled header
    in the PRECOMPILED_HEADER_USERS variable:

    - The precompiled header should not change what actually gets
      compiled.  Therefore, use the precompiled header only when
      compiling source files that start with including
      "git-compat-util.h" (directly or indirectly, e.g. via
      "builtin.h"), or its inclusion is only preceeded by #define
      directives that don't influence "git-compat-util.h" between its
      include guards [2] (currently DISABLE_SIGN_COMPARE_WARNINGS,
      USE_THE_REPOSITORY_VARIABLE or GIT_TEST_PROGRESS_ONLY). [3]

      Several (but not all) object or source files listed in the
      COMPAT_OBJS, REFTABLE_OBJS and THIRD_PARTY_SOURCES variables
      don't include "git-compat-util.h", therefore, for the sake of
      simplicity, none of the files listed in these variables are
      built with the precompiled header. [4]

      Since 671df48df8 the Meson build uses the precompiled header
      even when compiling those reftable source files that don't
      include "git-compat-util.h" at all, although this change is not
      mentioned in the commit message.

    - But other than that, use the precompiled header when compiling
      all other source files, including e.g. source files for
      standalone executables (e.g. "daemon.c" for "git-daemon"), or
      those in the directories "t/helper/" and "t/unit-tests/" as
      well.

      The Meson build, however, only uses the precompiled header for
      compiling objects in "libgit_sources" and "builtin_sources",
      despite 671df48df8 giving the impression that the precompiled
      header is included in all compilation units.

    - In short, PRECOMPILED_HEADER_USERS contains all object files
      listed in OBJECTS, except those that are listed in COMPAT_OBJS,
      REFTABLE_OBJS or THIRD_PARTY_SOURCES as well.

  - Add a new rule to build object files listed in
    PRECOMPILED_HEADER_USERS with the precompiled header.

    This rule and its dependencies are basically the same as our
    existing rule and its dependencies compiling object files from our
    source files, except:

    - This rule depends on the precompiled header as well, to make
      sure that it's built before it is used.

    - Use the "-include tools/precompiled.h" option to make the
      precompiled header the first header in the compilation unit,
      because only then is it used to speed things up.

    - Use the "-Winvalid-pch" option to catch any issues when the
      precompiled header is present but can't be used for whatever
      reason.  While being unable to use the precompiled header would
      normally only result in a slower build, it is probably better
      that developers are made aware that simething is not quite
      right.  Meson uses this option as well when compiling a source
      file using the precompiled header.

      Note, that in case of such an issue with "-Winvalid-pch" we
      would get a warning for each object file that is build using the
      precompiled header, but together with "-Werror" (e.g. with
      DEVELOPER=1) it would fail the build.

    Object files not listed in PRECOMPILED_HEADER_USERS are built with
    the existing (and unchanged) rule for object files.

  - This way the precompiled header is compiled only once during
    the whole build process.

    The Meson build, however, currently compiles the precompiled
    header twice: once for "libgit_sources" and once for
    "builtin_sources", despite 671df48df8 giving the impression that
    it's compiled only once.  And, by the looks of it, it would have
    to be compiled once more for each new library or executable where
    we declare the use of the precompiled header.

  - Add the Makefile knob NO_PRECOMPILED_HEADER to make it possible to
    build without using the precompiled header for testing purposes,
    or for any compiler that might be out there that doesn't support
    the "-Winvalid-pch" option.

    Note, that when this knob is set then we merely leave
    PRECOMPILED_HEADER_USERS empty: this way nothing is built with the
    precompiled header, but "make clean NO_PRECOMPILED_HEADER=1" would
    still remove a leftover precompiled header file.

With this patch series on top of v2.55.0 I got the following build
time improvement:

  Benchmark 1: make -j12 (rev = v2.55.0)
    Time (mean ± σ):     29.414 s ±  0.031 s    [User: 254.786 s, System: 47.447 s]
    Range (min … max):   29.370 s … 29.470 s    10 runs

  Benchmark 2: make -j12 (rev = precompile)
    Time (mean ± σ):     21.725 s ±  0.047 s    [User: 186.047 s, System: 35.109 s]
    Range (min … max):   21.643 s … 21.768 s    10 runs

  Summary
    'make -j12 (rev = precompile)' ran
      1.35 ± 0.00 times faster than 'make -j12 (rev = v2.55.0)'

[1] "make" applies target-specific variables to the first target's
    dependencies as well.  So, if the rule creating the precompiled
    header included $(EXTRA_CPPFLAGS) as well, then we could get this:

      $ make -s clean
      $ make V=1 git
      gcc -o tools/precompiled.h.gch -c -MF [...] -DSHELL_PATH='"/bin/sh"' '-DGIT_HTML_PATH="share/doc/git-doc"' '-DGIT_MAN_PATH="share/man"' '-DGIT_INFO_PATH="share/info"' tools/precompiled.h
      gcc -o git.o -c -include tools/precompiled.h -Winvalid-pch -MF [...] -DSHELL_PATH='"/bin/sh"' '-DGIT_HTML_PATH="share/doc/git-doc"' '-DGIT_MAN_PATH="share/man"' '-DGIT_INFO_PATH="share/info"' git.c
      gcc -o builtin/add.o -c -include tools/precompiled.h -Winvalid-pch -MF [...] -DSHELL_PATH='"/bin/sh"'  builtin/add.c
      cc1: error: ./tools/precompiled.h.gch: not used because `GIT_MAN_PATH' not defined [-Werror=invalid-pch]
      cc1: all warnings being treated as errors
      make: *** [Makefile:2940: builtin/add.o] Error 1

    So in this case "git.o" is the first object file to be build, and
    since it has a target-specific EXTRA_CPPFLAGS and since it depends
    on the precompiled header, the precompiled header is built with
    the same EXTRA_CPPFLAGS as well.  But then "builtin/add.o" is
    built with empty EXTRA_CPPFLAGS, and GCC's sanity checks for the
    -Winvalid-pch option complain.  Clang apparently doesn't consider
    this to be an issue, and builds "git" just fine.

    Note, however, that if the first object file to be built is not
    "git.o" (or one of the other object files with target-specific
    EXTRA_CPPFLAGS), which is usually the case with e.g. "make all",
    then the precompiled header is built with empty EXTRA_CPPFLAGS,
    and then all is well.  Weird.  We already had issues with "make"
    and target-specific variables in the past, see a673cfede6
    (Makefile: Fix occasional GIT-CFLAGS breakage, 2010-03-19).
    The Meson build doesn't use target-specific variables, and the
    whole project needs to be rebuilt when e.g. "mandir" is changed,
    although this is not mentioned in 904339edbd (Introduce support
    for the Meson build system, 2024-12-06).

[2] See baa61e46da (git-compat-util.h: move warning infra to prepare
    for PCHs, 2026-03-19).

[3] This can be verified by simply scanning through the output of:

    {
            printf '%s\n' 'print-%:'
            printf '\t%s\n' '@printf "%s\n" $($*)'
    } >/tmp/printvars.mak
    for f in $(make -f /tmp/printvars.mak -f Makefile print-PRECOMPILED_HEADER_USERS)
    do
            f="${f%o}c"
            sed -n -E -e "s%# *(define|include).*%&    $f%p" -e '/# *include/q' "$f"
    done | sort

[4] "make"'s flexibility would allow us to separately list those
    object files that don't include "git-compat-util.h", but then on
    my (I assume fairly typical) Linux box the number of object files
    built using the precompiled header increases only by 9 (from 536
    to 545), which reduces the build time by about 1% (0.2s).
    Therefore, I don't think it's worth the churn.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
---
 .gitignore |  1 +
 Makefile   | 26 +++++++++++++++++++++-----
 2 files changed, 22 insertions(+), 5 deletions(-)

diff --git a/.gitignore b/.gitignore
index 4da58c6754..0209bd16f2 100644
--- a/.gitignore
+++ b/.gitignore
@@ -233,6 +233,7 @@
 /.vscode/
 /tags
 /TAGS
+/tools/precompiled.h.gch
 /cscope*
 /compile_commands.json
 /.cache/
diff --git a/Makefile b/Makefile
index 2c4d6f4d4a..02162719db 100644
--- a/Makefile
+++ b/Makefile
@@ -321,6 +321,9 @@ include shared.mak
 # dependency rules.  The default is "auto", which means to use computed header
 # dependencies if your compiler is detected to support it.
 #
+# Define NO_PRECOMPILED_HEADER if you want to build Git without precompiling
+# "git-compat-util.h".
+#
 # Define NATIVE_CRLF if your platform uses CRLF for line endings.
 #
 # Define GIT_USER_AGENT if you want to change how git identifies itself during
@@ -2905,8 +2908,15 @@ endif
 .PHONY: objects
 objects: $(OBJECTS)
 
-dep_files := $(foreach f,$(OBJECTS),$(dir $f).depend/$(notdir $f).d)
-dep_dirs := $(addsuffix .depend,$(sort $(dir $(OBJECTS))))
+PRECOMPILED_HEADER := tools/precompiled.h
+PRECOMPILED_HEADER_GCH := $(addsuffix .gch,$(PRECOMPILED_HEADER))
+
+ifndef NO_PRECOMPILED_HEADER
+PRECOMPILED_HEADER_USERS := $(filter-out $(COMPAT_OBJS) $(REFTABLE_OBJS) $(patsubst %.c,%.o,$(THIRD_PARTY_SOURCES)),$(OBJECTS))
+endif
+
+dep_files := $(foreach f,$(OBJECTS) $(PRECOMPILED_HEADER_GCH),$(dir $f).depend/$(notdir $f).d)
+dep_dirs := $(addsuffix .depend,$(sort $(dir $(OBJECTS) $(PRECOMPILED_HEADER_GCH))))
 
 ifeq ($(uname_S),Darwin)
 	dep_dirs += $(addsuffix .depend,$(sort $(dir contrib/credential/osxkeychain/git-credential-osxkeychain.o)))
@@ -2940,7 +2950,13 @@ missing_compdb_dir =
 compdb_args =
 endif
 
-$(OBJECTS): %.o: %.c GIT-CFLAGS $(missing_dep_dirs) $(missing_compdb_dir)
+$(PRECOMPILED_HEADER_GCH): %.gch: % GIT-CFLAGS $(missing_dep_dirs) $(missing_compdb_dir)
+	$(QUIET_CC)$(CC) -o $@ -c $(dep_args) $(compdb_args) $(ALL_CFLAGS) $<
+
+$(PRECOMPILED_HEADER_USERS): %.o: %.c $(PRECOMPILED_HEADER_GCH) GIT-CFLAGS $(missing_dep_dirs) $(missing_compdb_dir)
+	$(QUIET_CC)$(CC) -o $*.o -c -include $(PRECOMPILED_HEADER) -Winvalid-pch $(dep_args) $(compdb_args) $(ALL_CFLAGS) $(EXTRA_CPPFLAGS) $<
+
+$(filter-out $(PRECOMPILED_HEADER_USERS),$(OBJECTS)): %.o: %.c GIT-CFLAGS $(missing_dep_dirs) $(missing_compdb_dir)
 	$(QUIET_CC)$(CC) -o $*.o -c $(dep_args) $(compdb_args) $(ALL_CFLAGS) $(EXTRA_CPPFLAGS) $<
 
 %.s: %.c GIT-CFLAGS FORCE
@@ -2954,7 +2970,7 @@ ifneq ($(dep_files_present),)
 include $(dep_files_present)
 endif
 else
-$(OBJECTS): $(LIB_H) $(GENERATED_H)
+$(OBJECTS) $(PRECOMPILED_HEADER_GCH): $(LIB_H) $(GENERATED_H)
 endif
 
 ifeq ($(GENERATE_COMPILATION_DATABASE),yes)
@@ -3908,7 +3924,7 @@ clean: profile-clean coverage-clean cocciclean
 	$(RM) GIT-TEST-SUITES
 	$(RM) po/git.pot po/git-core.pot
 	$(RM) git.rc git.res
-	$(RM) $(OBJECTS)
+	$(RM) $(OBJECTS) $(PRECOMPILED_HEADER_GCH)
 	$(RM) headless-git.o
 	$(RM) $(LIB_FILE)
 	$(RM) $(ALL_PROGRAMS) $(SCRIPT_LIB) $(BUILT_INS) $(OTHER_PROGRAMS)
-- 
2.55.0.1193.g1b994e35de

Re: [PATCH 4/4] Makefile: precompile "git-compat-util.h"

[SZEDER Gábor]

On Wed, Sep 09, 2026 at 09:50:06PM +0200, SZEDER Gábor wrote:
>   - List the object files that are built using the precompiled header
>     in the PRECOMPILED_HEADER_USERS variable:
> 
>     - The precompiled header should not change what actually gets
>       compiled.  Therefore, use the precompiled header only when
>       compiling source files that start with including
>       "git-compat-util.h" (directly or indirectly, e.g. via
>       "builtin.h"), or its inclusion is only preceeded by #define
>       directives that don't influence "git-compat-util.h" between its
>       include guards [2] (currently DISABLE_SIGN_COMPARE_WARNINGS,
>       USE_THE_REPOSITORY_VARIABLE or GIT_TEST_PROGRESS_ONLY). [3]
> 
>       Several (but not all) object or source files listed in the
>       COMPAT_OBJS, REFTABLE_OBJS and THIRD_PARTY_SOURCES variables
>       don't include "git-compat-util.h", therefore, for the sake of
>       simplicity, none of the files listed in these variables are
>       built with the precompiled header. [4]

>     - In short, PRECOMPILED_HEADER_USERS contains all object files
>       listed in OBJECTS, except those that are listed in COMPAT_OBJS,
>       REFTABLE_OBJS or THIRD_PARTY_SOURCES as well.

> [4] "make"'s flexibility would allow us to separately list those
>     object files that don't include "git-compat-util.h", but then on
>     my (I assume fairly typical) Linux box the number of object files
>     built using the precompiled header increases only by 9 (from 536
>     to 545), which reduces the build time by about 1% (0.2s).
>     Therefore, I don't think it's worth the churn.

For reference, a change to do that would look like that patch below,
but, as mentioned above, the benefit is rather small:

  Benchmark 1: make -j12 (rev = precompile)
    Time (mean ± σ):     21.747 s ±  0.048 s    [User: 186.120 s, System: 35.032 s]
    Range (min … max):   21.650 s … 21.802 s    10 runs

  Benchmark 2: make -j12 (rev = precompile-all)
    Time (mean ± σ):     21.556 s ±  0.062 s    [User: 184.584 s, System: 35.016 s]
    Range (min … max):   21.477 s … 21.675 s    10 runs

  Summary
    'make -j12 (rev = precompile-all)' ran
      1.01 ± 0.00 times faster than 'make -j12 (rev = precompile)'

  --- >8 ---

diff --git a/Makefile b/Makefile
index 7d9dac83c4..b5d75dc75f 100644
--- a/Makefile
+++ b/Makefile
@@ -698,6 +698,7 @@ BUILTIN_OBJS =
 BUILT_INS =
 COMPAT_CFLAGS =
 COMPAT_OBJS =
+COMPAT_NOPCH_OBJS =
 GENERATED_H =
 EXTRA_CPPFLAGS =
 FUZZ_OBJS =
@@ -711,6 +712,7 @@ OTHER_PROGRAMS =
 PROGRAM_OBJS =
 PROGRAMS =
 REFTABLE_OBJS =
+REFTABLE_NOPCH_OBJS =
 RUST_SOURCES =
 EXCLUDED_PROGRAMS =
 SCRIPT_PERL =
@@ -721,6 +723,7 @@ TEST_BUILTINS_OBJS =
 TEST_OBJS =
 TEST_PROGRAMS_NEED_X =
 THIRD_PARTY_SOURCES =
+THIRD_PARTY_NOPCH_SOURCES =
 UNIT_TEST_PROGRAMS =
 UNIT_TEST_DIR = t/unit-tests
 UNIT_TEST_BIN = $(UNIT_TEST_DIR)/bin
@@ -1376,20 +1379,22 @@ LIB_OBJS += xdiff/xpatience.o
 LIB_OBJS += xdiff/xprepare.o
 LIB_OBJS += xdiff/xutils.o
 
-REFTABLE_OBJS += reftable/basics.o
-REFTABLE_OBJS += reftable/block.o
-REFTABLE_OBJS += reftable/blocksource.o
-REFTABLE_OBJS += reftable/error.o
-REFTABLE_OBJS += reftable/fsck.o
-REFTABLE_OBJS += reftable/iter.o
-REFTABLE_OBJS += reftable/merged.o
-REFTABLE_OBJS += reftable/pq.o
-REFTABLE_OBJS += reftable/record.o
-REFTABLE_OBJS += reftable/stack.o
 REFTABLE_OBJS += reftable/system.o
-REFTABLE_OBJS += reftable/table.o
-REFTABLE_OBJS += reftable/tree.o
-REFTABLE_OBJS += reftable/writer.o
+REFTABLE_NOPCH_OBJS += reftable/basics.o
+REFTABLE_NOPCH_OBJS += reftable/block.o
+REFTABLE_NOPCH_OBJS += reftable/blocksource.o
+REFTABLE_NOPCH_OBJS += reftable/error.o
+REFTABLE_NOPCH_OBJS += reftable/fsck.o
+REFTABLE_NOPCH_OBJS += reftable/iter.o
+REFTABLE_NOPCH_OBJS += reftable/merged.o
+REFTABLE_NOPCH_OBJS += reftable/pq.o
+REFTABLE_NOPCH_OBJS += reftable/record.o
+REFTABLE_NOPCH_OBJS += reftable/stack.o
+REFTABLE_NOPCH_OBJS += reftable/table.o
+REFTABLE_NOPCH_OBJS += reftable/tree.o
+REFTABLE_NOPCH_OBJS += reftable/writer.o
+
+REFTABLE_OBJS += $(REFTABLE_NOPCH_OBJS)
 
 LIB_OBJS += $(REFTABLE_OBJS)
 
@@ -1535,11 +1540,13 @@ THIRD_PARTY_SOURCES += compat/inet_ntop.c
 THIRD_PARTY_SOURCES += compat/inet_pton.c
 THIRD_PARTY_SOURCES += compat/obstack.%
 THIRD_PARTY_SOURCES += compat/poll/%
-THIRD_PARTY_SOURCES += compat/regex/%
-THIRD_PARTY_SOURCES += sha1collisiondetection/%
-THIRD_PARTY_SOURCES += sha1dc/%
-THIRD_PARTY_SOURCES += $(UNIT_TEST_DIR)/clar/%
-THIRD_PARTY_SOURCES += $(UNIT_TEST_DIR)/clar/clar/%
+THIRD_PARTY_NOPCH_SOURCES += compat/regex/%
+THIRD_PARTY_NOPCH_SOURCES += sha1collisiondetection/%
+THIRD_PARTY_NOPCH_SOURCES += sha1dc/%
+THIRD_PARTY_NOPCH_SOURCES += $(UNIT_TEST_DIR)/clar/%
+THIRD_PARTY_NOPCH_SOURCES += $(UNIT_TEST_DIR)/clar/clar/%
+
+THIRD_PARTY_SOURCES += $(THIRD_PARTY_NOPCH_SOURCES)
 
 CLAR_TEST_SUITES += u-ctype
 CLAR_TEST_SUITES += u-dir
@@ -1959,7 +1966,7 @@ ifdef SNPRINTF_RETURNS_BOGUS
 endif
 ifdef FREAD_READS_DIRECTORIES
 	COMPAT_CFLAGS += -DFREAD_READS_DIRECTORIES
-	COMPAT_OBJS += compat/fopen.o
+	COMPAT_NOPCH_OBJS += compat/fopen.o
 endif
 ifdef OPEN_RETURNS_EINTR
 	COMPAT_CFLAGS += -DOPEN_RETURNS_EINTR
@@ -2063,7 +2070,7 @@ ifdef NO_TRUSTABLE_FILEMODE
 endif
 ifdef NEEDS_MODE_TRANSLATION
 	COMPAT_CFLAGS += -DNEEDS_MODE_TRANSLATION
-	COMPAT_OBJS += compat/stat.o
+	COMPAT_NOPCH_OBJS += compat/stat.o
 endif
 ifdef NO_IPV6
 	BASIC_CFLAGS += -DNO_IPV6
@@ -2229,7 +2236,7 @@ ifdef SHA1_MAX_BLOCK_SIZE
 endif
 ifdef NO_HSTRERROR
 	COMPAT_CFLAGS += -DNO_HSTRERROR
-	COMPAT_OBJS += compat/hstrerror.o
+	COMPAT_NOPCH_OBJS += compat/hstrerror.o
 endif
 ifdef NO_MEMMEM
 	COMPAT_CFLAGS += -DNO_MEMMEM
@@ -2282,7 +2289,7 @@ ifdef UNRELIABLE_FSTAT
 endif
 ifdef NO_REGEX
 	COMPAT_CFLAGS += -Icompat/regex
-	COMPAT_OBJS += compat/regex/regex.o
+	COMPAT_NOPCH_OBJS += compat/regex/regex.o
 else
 ifdef USE_ENHANCED_BASIC_REGULAR_EXPRESSIONS
 	COMPAT_CFLAGS += -DUSE_ENHANCED_BASIC_REGULAR_EXPRESSIONS
@@ -2387,17 +2394,17 @@ endif
 
 ifdef FILENO_IS_A_MACRO
 	COMPAT_CFLAGS += -DFILENO_IS_A_MACRO
-	COMPAT_OBJS += compat/fileno.o
+	COMPAT_NOPCH_OBJS += compat/fileno.o
 endif
 
 ifdef NEED_ACCESS_ROOT_HANDLER
 	COMPAT_CFLAGS += -DNEED_ACCESS_ROOT_HANDLER
-	COMPAT_OBJS += compat/access.o
+	COMPAT_NOPCH_OBJS += compat/access.o
 endif
 
 ifdef FSMONITOR_DAEMON_BACKEND
 	COMPAT_CFLAGS += -DHAVE_FSMONITOR_DAEMON_BACKEND
-	COMPAT_OBJS += compat/fsmonitor/fsm-listen-$(FSMONITOR_DAEMON_BACKEND).o
+	COMPAT_NOPCH_OBJS += compat/fsmonitor/fsm-listen-$(FSMONITOR_DAEMON_BACKEND).o
 	COMPAT_OBJS += compat/fsmonitor/fsm-health-$(FSMONITOR_DAEMON_BACKEND).o
 endif
 
@@ -2531,6 +2538,7 @@ endif
 LIBS = $(filter-out %.o, $(GITLIBS)) $(EXTLIBS)
 
 BASIC_CFLAGS += $(COMPAT_CFLAGS)
+COMPAT_OBJS += $(COMPAT_NOPCH_OBJS)
 LIB_OBJS += $(COMPAT_OBJS)
 
 # Quote for C
@@ -2912,7 +2920,7 @@ PRECOMPILED_HEADER := tools/precompiled.h
 PRECOMPILED_HEADER_GCH := $(addsuffix .gch,$(PRECOMPILED_HEADER))
 
 ifndef NO_PRECOMPILED_HEADER
-PRECOMPILED_HEADER_USERS := $(filter-out $(COMPAT_OBJS) $(REFTABLE_OBJS) $(patsubst %.c,%.o,$(THIRD_PARTY_SOURCES)),$(OBJECTS))
+PRECOMPILED_HEADER_USERS := $(filter-out $(COMPAT_NOPCH_OBJS) $(REFTABLE_NOPCH_OBJS) $(patsubst %.c,%.o,$(THIRD_PARTY_NOPCH_SOURCES)),$(OBJECTS))
 endif
 
 dep_files := $(foreach f,$(OBJECTS) $(PRECOMPILED_HEADER_GCH),$(dir $f).depend/$(notdir $f).d)
diff --git a/config.mak.uname b/config.mak.uname
index 95ef6e64dc..c51ebadc40 100644
--- a/config.mak.uname
+++ b/config.mak.uname
@@ -152,7 +152,7 @@ ifeq ($(uname_S),Darwin)
 	NO_MEMMEM = YesPlease
 	USE_ST_TIMESPEC = YesPlease
 	HAVE_DEV_TTY = YesPlease
-	COMPAT_OBJS += compat/precompose_utf8.o
+	COMPAT_NOPCH_OBJS += compat/precompose_utf8.o
 	BASIC_CFLAGS += -DPRECOMPOSE_UNICODE
 	BASIC_CFLAGS += -DPROTECT_HFS_DEFAULT=1
 	HAVE_BSD_SYSCTL = YesPlease
@@ -535,7 +535,8 @@ endif
 	AR = compat/vcbuild/scripts/lib.pl
 	CFLAGS =
 	BASIC_CFLAGS = -nologo -I. -Icompat/vcbuild/include -DWIN32 -D_CONSOLE -DHAVE_STRING_H -D_CRT_SECURE_NO_WARNINGS -D_CRT_NONSTDC_NO_DEPRECATE
-	COMPAT_OBJS = compat/msvc.o compat/winansi.o \
+	COMPAT_NOPCH_OBJS = compat/winansi.o
+	COMPAT_OBJS = compat/msvc.o \
 		compat/win32/flush.o \
 		compat/win32/path-utils.o \
 		compat/win32/pthread.o compat/win32/syslog.o \
@@ -735,7 +736,8 @@ ifeq ($(uname_S),MINGW)
 	BASIC_LDFLAGS += -municode
 	COMPAT_CFLAGS += -DNOGDI -Icompat -Icompat/win32
 	COMPAT_CFLAGS += -DSTRIP_EXTENSION=\".exe\"
-	COMPAT_OBJS += compat/mingw.o compat/winansi.o \
+	COMPAT_NOPCH_OBJS += compat/winansi.o
+	COMPAT_OBJS += compat/mingw.o \
 		compat/win32/trace2_win32_process_info.o \
 		compat/win32/flush.o \
 		compat/win32/path-utils.o \
diff --git a/contrib/buildsystems/CMakeLists.txt b/contrib/buildsystems/CMakeLists.txt
index 462c1eb5ec..d96a4ebd84 100644
--- a/contrib/buildsystems/CMakeLists.txt
+++ b/contrib/buildsystems/CMakeLists.txt
@@ -101,7 +101,7 @@ project(git
 #macros for parsing the Makefile for sources and scripts
 macro(parse_makefile_for_sources list_var makefile regex)
 	file(STRINGS ${makefile} ${list_var} REGEX "^${regex} \\+=(.*)")
-	string(REPLACE "${regex} +=" "" ${list_var} ${${list_var}})
+	string(REGEX REPLACE "${regex} \\+=" "" ${list_var} ${${list_var}})
 	string(REGEX REPLACE "\\$\\([^)]*_OBJS\\)" "" ${list_var} ${${list_var}}) # remove any "$(*_OBJS)" variables
 	string(STRIP ${${list_var}} ${list_var}) #remove trailing/leading whitespaces
 	string(REPLACE ".o" ".c;" ${list_var} ${${list_var}}) #change .o to .c, ; is for converting the string into a list
@@ -669,7 +669,7 @@ include_directories(${CMAKE_BINARY_DIR})
 parse_makefile_for_sources(libgit_SOURCES ${CMAKE_SOURCE_DIR}/Makefile "LIB_OBJS")
 
 #reftable
-parse_makefile_for_sources(reftable_SOURCES ${CMAKE_SOURCE_DIR}/Makefile "REFTABLE_OBJS")
+parse_makefile_for_sources(reftable_SOURCES ${CMAKE_SOURCE_DIR}/Makefile "REFTABLE_(|NOPCH_)OBJS")
 list(APPEND libgit_SOURCES ${reftable_SOURCES})
 
 list(TRANSFORM libgit_SOURCES PREPEND "${CMAKE_SOURCE_DIR}/")
-- 
2.55.0.1193.g1b994e35de

Re: [PATCH 3/4] Makefile: reintroduce REFTABLE_OBJS

[Junio C Hamano]

SZEDER Gábor <szeder.dev@gmail.com> writes:

> Object files under "reftable/" used to be listed in the REFTABLE_OBJS
> Makefile variable so we could build a static library from them.  This
> static library was removed in f3b4c89d59 (make: delete REFTABLE_LIB,
> add reftable to LIB_OBJS, 2025-10-02), along with filling
> REFTALBE_OBJS with object files.
>
> However, the reftable source files are kind of special, because the
> reftable implementation is supposed to be easily includable in other
> projects.  Therefore, the reftable source files don't include
> "git-compat-util.h", with the sole exception of the purposefully
> project-specific "reftable/system.c".  Consequently, they shouldn't be
> compiled with our precompiled header, as it does include
> "git-compat-util.h".

This is the first mention of "our precompiled header" in this
series, and the first hint that "our precompiled header" would
include "git-compat-util.h".  It may probably give us a better
organization to state it upfront at the beginning of the proposed
log message of this commit.  It is of secondary importance that once
in the past we used to have REFTABLE_OBJS Makefile variable that
listed some files (but for completely different purposes).  How
about explaining it along this line...

    The ultimate endgame of this series is to use the precompiled
    header facility to speed up compilation, and the plan is to have
    Git specific headers including git-compat-util.h precompiled.

    The reftable sources are largely designed to be independent from
    the Git source proper, and except for reftable/system.c they do
    not include <git-compat-util.h>.

    Move the object files in the subsystem from the LIB_OBJS to the
    REFTABLE_OBJS Makefile variable, so that we can use LIB_OBJS as
    list of files compiled with precompiled header files and others
    without

... or something like that, perhaps?

[PATCH v2 0/4] make: precompile "git-compat-util.h"

[SZEDER Gábor]

Update our Makefile to make use of the recently introduced precompiled
header to make builds faster (on my setup by about 35%).

Changes since v1:
  - Update the commit message of patch 3/4 per Junio's suggestion.


SZEDER Gábor (4):
  Makefile: remove XDIFF_OBJS initialization
  cmake: remove any "$(*_OBJS)" variables when parsing Makefile for
    sources
  Makefile: reintroduce REFTABLE_OBJS
  Makefile: precompile "git-compat-util.h"

 .gitignore                          |  1 +
 Makefile                            | 59 +++++++++++++++++++----------
 contrib/buildsystems/CMakeLists.txt |  6 ++-
 3 files changed, 45 insertions(+), 21 deletions(-)

Range-diff against v1:
1:  d52a1476d1 = 1:  d52a1476d1 Makefile: remove XDIFF_OBJS initialization
2:  5d60181efd = 2:  5d60181efd cmake: remove any "$(*_OBJS)" variables when parsing Makefile for sources
3:  0296c6cffc ! 3:  cfc77c0b2c Makefile: reintroduce REFTABLE_OBJS
    @@ Metadata
      ## Commit message ##
         Makefile: reintroduce REFTABLE_OBJS
     
    -    Object files under "reftable/" used to be listed in the REFTABLE_OBJS
    -    Makefile variable so we could build a static library from them.  This
    -    static library was removed in f3b4c89d59 (make: delete REFTABLE_LIB,
    -    add reftable to LIB_OBJS, 2025-10-02), along with filling
    -    REFTALBE_OBJS with object files.
    +    In the next commit we are about to precompile "git-compat-util.h" with
    +    "make" to reduce build times.  But using the precompiled header should
    +    not change what actually gets compiled, therefore a source file can
    +    only be compiled using the precompiled header if the first included
    +    header file is "git-compat-util.h".
     
    -    However, the reftable source files are kind of special, because the
    -    reftable implementation is supposed to be easily includable in other
    -    projects.  Therefore, the reftable source files don't include
    +    The reftable source files are kind of special, because the reftable
    +    implementation is supposed to be easily includable in other projects.
    +    Therefore, the reftable source files don't include
         "git-compat-util.h", with the sole exception of the purposefully
         project-specific "reftable/system.c".  Consequently, they shouldn't be
    -    compiled with our precompiled header, as it does include
    -    "git-compat-util.h".
    +    compiled with our precompiled header.
    +
    +    List object files under "reftable" in the REFTABLE_OBJS Makefile
    +    variable, so in the next commit we'll be able to easily filter them
    +    out and keep building them the old way, without the precompiled
    +    header.
     
    -    Resurrect listing object files under "reftable/" in REFTABLE_OBJS (but
    -    not the static library), so in the next commit we'll be able to easily
    -    filter them out and keep building them the old way, without the
    -    precompiled header.
    +    Note that object files under "reftable/" used to be listed in
    +    REFTABLE_OBJS so we could build a static library from them.  This
    +    static library was removed in f3b4c89d59 (make: delete REFTABLE_LIB,
    +    add reftable to LIB_OBJS, 2025-10-02), along with filling
    +    REFTALBE_OBJS with object files.  This change essentially reverts the
    +    removal of REFTABLE_OBJS, but not the building of that static library.
     
         Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
     
4:  ce9fd91413 = 4:  a933be0664 Makefile: precompile "git-compat-util.h"
-- 
2.56.0.rc0.467.ge054dd0dd6

[PATCH v2 1/4] Makefile: remove XDIFF_OBJS initialization

[SZEDER Gábor]

Object files under 'xlib/' used to be listed in the XDIFF_OBJS
Makefile variable so we could build a static library from them.  This
static library was removed in cf680cdb95 (make: delete XDIFF_LIB, add
xdiff to LIB_OBJS, 2025-10-02), along with filling XDIFF_OBJS with
object files.

But the initial empty initalization of XDIFF_OBJS remained, so remove
it now.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
---
 Makefile | 1 -
 1 file changed, 1 deletion(-)

diff --git a/Makefile b/Makefile
index d4b775953d..7d9ac15c74 100644
--- a/Makefile
+++ b/Makefile
@@ -695,7 +695,6 @@ BUILTIN_OBJS =
 BUILT_INS =
 COMPAT_CFLAGS =
 COMPAT_OBJS =
-XDIFF_OBJS =
 GENERATED_H =
 EXTRA_CPPFLAGS =
 FUZZ_OBJS =
-- 
2.56.0.rc0.467.ge054dd0dd6

[PATCH v2 2/4] cmake: remove any "$(*_OBJS)" variables when parsing Makefile for sources

[SZEDER Gábor]

To get various lists of files, CMake parses our Makefile looking for
lines matching e.g. "list_var += ...".  In case of LIB_OBJS this
picks up the line "LIB_OBJS += $(COMPAT_OBJS)" as well, so the parsing
macro has a specific instruction to remove "$(COMPAT_OBJS)" from the
resulting list.

Currently this is the only such Makefile variable to be removed from
the list, but the next patches will (re)introduce more variables
containing lists of object files, so let's generalize that removing
instruction to remove any "$(*_OBJS)" Makefile variable as well.

Note that we can't make the pattern matching the Makefile variable too
general, e.g. to match any "$(VARIABLE)", because some lines of our
Makefile do contain variables as directory prefixes, e.g.
"UNIT_TEST_OBJS += $(UNIT_TEST_DIR)/test-lib.o", and we must
definitely keep those.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
---
 contrib/buildsystems/CMakeLists.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/contrib/buildsystems/CMakeLists.txt b/contrib/buildsystems/CMakeLists.txt
index 8f56203f34..241da0d43a 100644
--- a/contrib/buildsystems/CMakeLists.txt
+++ b/contrib/buildsystems/CMakeLists.txt
@@ -102,7 +102,7 @@ project(git
 macro(parse_makefile_for_sources list_var makefile regex)
 	file(STRINGS ${makefile} ${list_var} REGEX "^${regex} \\+=(.*)")
 	string(REPLACE "${regex} +=" "" ${list_var} ${${list_var}})
-	string(REPLACE "$(COMPAT_OBJS)" "" ${list_var} ${${list_var}}) #remove "$(COMPAT_OBJS)" This is only for libgit.
+	string(REGEX REPLACE "\\$\\([^)]*_OBJS\\)" "" ${list_var} ${${list_var}}) # remove any "$(*_OBJS)" variables
 	string(STRIP ${${list_var}} ${list_var}) #remove trailing/leading whitespaces
 	string(REPLACE ".o" ".c;" ${list_var} ${${list_var}}) #change .o to .c, ; is for converting the string into a list
 	list(TRANSFORM ${list_var} STRIP) #remove trailing/leading whitespaces for each element in list
-- 
2.56.0.rc0.467.ge054dd0dd6

[PATCH v2 3/4] Makefile: reintroduce REFTABLE_OBJS

[SZEDER Gábor]

In the next commit we are about to precompile "git-compat-util.h" with
"make" to reduce build times.  But using the precompiled header should
not change what actually gets compiled, therefore a source file can
only be compiled using the precompiled header if the first included
header file is "git-compat-util.h".

The reftable source files are kind of special, because the reftable
implementation is supposed to be easily includable in other projects.
Therefore, the reftable source files don't include
"git-compat-util.h", with the sole exception of the purposefully
project-specific "reftable/system.c".  Consequently, they shouldn't be
compiled with our precompiled header.

List object files under "reftable" in the REFTABLE_OBJS Makefile
variable, so in the next commit we'll be able to easily filter them
out and keep building them the old way, without the precompiled
header.

Note that object files under "reftable/" used to be listed in
REFTABLE_OBJS so we could build a static library from them.  This
static library was removed in f3b4c89d59 (make: delete REFTABLE_LIB,
add reftable to LIB_OBJS, 2025-10-02), along with filling
REFTALBE_OBJS with object files.  This change essentially reverts the
removal of REFTABLE_OBJS, but not the building of that static library.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
---
 Makefile                            | 32 ++++++++++++++++-------------
 contrib/buildsystems/CMakeLists.txt |  4 ++++
 2 files changed, 22 insertions(+), 14 deletions(-)

diff --git a/Makefile b/Makefile
index 7d9ac15c74..2c4d6f4d4a 100644
--- a/Makefile
+++ b/Makefile
@@ -707,6 +707,7 @@ OBJECTS =
 OTHER_PROGRAMS =
 PROGRAM_OBJS =
 PROGRAMS =
+REFTABLE_OBJS =
 RUST_SOURCES =
 EXCLUDED_PROGRAMS =
 SCRIPT_PERL =
@@ -1284,20 +1285,6 @@ LIB_OBJS += refs/iterator.o
 LIB_OBJS += refs/packed-backend.o
 LIB_OBJS += refs/ref-cache.o
 LIB_OBJS += refspec.o
-LIB_OBJS += reftable/basics.o
-LIB_OBJS += reftable/block.o
-LIB_OBJS += reftable/blocksource.o
-LIB_OBJS += reftable/error.o
-LIB_OBJS += reftable/fsck.o
-LIB_OBJS += reftable/iter.o
-LIB_OBJS += reftable/merged.o
-LIB_OBJS += reftable/pq.o
-LIB_OBJS += reftable/record.o
-LIB_OBJS += reftable/stack.o
-LIB_OBJS += reftable/system.o
-LIB_OBJS += reftable/table.o
-LIB_OBJS += reftable/tree.o
-LIB_OBJS += reftable/writer.o
 LIB_OBJS += remote.o
 LIB_OBJS += repack.o
 LIB_OBJS += repack-cruft.o
@@ -1386,6 +1373,23 @@ LIB_OBJS += xdiff/xpatience.o
 LIB_OBJS += xdiff/xprepare.o
 LIB_OBJS += xdiff/xutils.o
 
+REFTABLE_OBJS += reftable/basics.o
+REFTABLE_OBJS += reftable/block.o
+REFTABLE_OBJS += reftable/blocksource.o
+REFTABLE_OBJS += reftable/error.o
+REFTABLE_OBJS += reftable/fsck.o
+REFTABLE_OBJS += reftable/iter.o
+REFTABLE_OBJS += reftable/merged.o
+REFTABLE_OBJS += reftable/pq.o
+REFTABLE_OBJS += reftable/record.o
+REFTABLE_OBJS += reftable/stack.o
+REFTABLE_OBJS += reftable/system.o
+REFTABLE_OBJS += reftable/table.o
+REFTABLE_OBJS += reftable/tree.o
+REFTABLE_OBJS += reftable/writer.o
+
+LIB_OBJS += $(REFTABLE_OBJS)
+
 BUILTIN_OBJS += builtin/add.o
 BUILTIN_OBJS += builtin/am.o
 BUILTIN_OBJS += builtin/annotate.o
diff --git a/contrib/buildsystems/CMakeLists.txt b/contrib/buildsystems/CMakeLists.txt
index 241da0d43a..462c1eb5ec 100644
--- a/contrib/buildsystems/CMakeLists.txt
+++ b/contrib/buildsystems/CMakeLists.txt
@@ -668,6 +668,10 @@ include_directories(${CMAKE_BINARY_DIR})
 #libgit
 parse_makefile_for_sources(libgit_SOURCES ${CMAKE_SOURCE_DIR}/Makefile "LIB_OBJS")
 
+#reftable
+parse_makefile_for_sources(reftable_SOURCES ${CMAKE_SOURCE_DIR}/Makefile "REFTABLE_OBJS")
+list(APPEND libgit_SOURCES ${reftable_SOURCES})
+
 list(TRANSFORM libgit_SOURCES PREPEND "${CMAKE_SOURCE_DIR}/")
 list(TRANSFORM compat_SOURCES PREPEND "${CMAKE_SOURCE_DIR}/")
 
-- 
2.56.0.rc0.467.ge054dd0dd6

[PATCH v2 4/4] Makefile: precompile "git-compat-util.h"

[SZEDER Gábor]

This patch follows the idea of 671df48df8 (meson: precompile
"git-compat-util.h", 2026-03-19) to make it faster to build Git using
"make".  The notable differences are the boilerplate needed to wire up
the precompiled header with "make", and the selection of object files
that are built using the precompiled header:

  - Add a new rule to precompile "tools/precompiled.h" into
    "tools/precompiled.h.gch".

    This rule and its dependencies are basically the same as our
    existing rule and its dependencies for compiling object files from
    our source files and, except that in this rule we don't use the
    EXTRA_CPPFLAGS target-specific variable.  This is partly because
    any compiler flags in that target-specific variable can't possibly
    make sense for the project-wide "git-compat-util.h", and partly
    because it could run afoul of "make"'s quirks with target-specific
    variables and GCC's "-Winvalid-pch" compiler option [1].

    Our Makefile always writes object files next to the source files
    they were compiled from.  Since a precompiled header is in many
    ways similar to an object file, let's follow suit and write it
    next to the header file it was created from as well.  671df48df8
    doesn't mention why "precompiled.h" was placed in "tools/".

    Use the ".gch" suffix for the precompiled header file, because
    that's the only suffix GCC looks for when searching for a
    precompiled header.  Clang apparently looks for both ".pch" and
    ".gch" suffixes.  If we ever encounter a compiler which only
    supports a different precompiled header suffix, then we might make
    the suffix configurable via a Makefile knob; but until then it
    remains hard-coded for the sake of simplicity.

  - Declare the precompiled header's dependencies, so it gets rebuilt
    when any of our header files it includes is modified.

    When using computed header dependencies, then the compiler can
    generate the Makefile snippet containing the header files inlcuded
    by the precompiled header, just like when compiling a C source
    file into an object file.

    When not using computed header dependencies, then make the
    precompiled header depend on the same header files that our object
    files depend on, i.e. those listed in LIB_H and GENERATED_H.  This
    is not ideal, because the precompiled header will be rebuilt even
    when a header file it doesn't actually depend on changes; but in
    that case all object files will be rebuilt as well anyway.

  - List the object files that are built using the precompiled header
    in the PRECOMPILED_HEADER_USERS variable:

    - The precompiled header should not change what actually gets
      compiled.  Therefore, use the precompiled header only when
      compiling source files that start with including
      "git-compat-util.h" (directly or indirectly, e.g. via
      "builtin.h"), or its inclusion is only preceeded by #define
      directives that don't influence "git-compat-util.h" between its
      include guards [2] (currently DISABLE_SIGN_COMPARE_WARNINGS,
      USE_THE_REPOSITORY_VARIABLE or GIT_TEST_PROGRESS_ONLY). [3]

      Several (but not all) object or source files listed in the
      COMPAT_OBJS, REFTABLE_OBJS and THIRD_PARTY_SOURCES variables
      don't include "git-compat-util.h", therefore, for the sake of
      simplicity, none of the files listed in these variables are
      built with the precompiled header. [4]

      Since 671df48df8 the Meson build uses the precompiled header
      even when compiling those reftable source files that don't
      include "git-compat-util.h" at all, although this change is not
      mentioned in the commit message.

    - But other than that, use the precompiled header when compiling
      all other source files, including e.g. source files for
      standalone executables (e.g. "daemon.c" for "git-daemon"), or
      those in the directories "t/helper/" and "t/unit-tests/" as
      well.

      The Meson build, however, only uses the precompiled header for
      compiling objects in "libgit_sources" and "builtin_sources",
      despite 671df48df8 giving the impression that the precompiled
      header is included in all compilation units.

    - In short, PRECOMPILED_HEADER_USERS contains all object files
      listed in OBJECTS, except those that are listed in COMPAT_OBJS,
      REFTABLE_OBJS or THIRD_PARTY_SOURCES as well.

  - Add a new rule to build object files listed in
    PRECOMPILED_HEADER_USERS with the precompiled header.

    This rule and its dependencies are basically the same as our
    existing rule and its dependencies compiling object files from our
    source files, except:

    - This rule depends on the precompiled header as well, to make
      sure that it's built before it is used.

    - Use the "-include tools/precompiled.h" option to make the
      precompiled header the first header in the compilation unit,
      because only then is it used to speed things up.

    - Use the "-Winvalid-pch" option to catch any issues when the
      precompiled header is present but can't be used for whatever
      reason.  While being unable to use the precompiled header would
      normally only result in a slower build, it is probably better
      that developers are made aware that simething is not quite
      right.  Meson uses this option as well when compiling a source
      file using the precompiled header.

      Note, that in case of such an issue with "-Winvalid-pch" we
      would get a warning for each object file that is build using the
      precompiled header, but together with "-Werror" (e.g. with
      DEVELOPER=1) it would fail the build.

    Object files not listed in PRECOMPILED_HEADER_USERS are built with
    the existing (and unchanged) rule for object files.

  - This way the precompiled header is compiled only once during
    the whole build process.

    The Meson build, however, currently compiles the precompiled
    header twice: once for "libgit_sources" and once for
    "builtin_sources", despite 671df48df8 giving the impression that
    it's compiled only once.  And, by the looks of it, it would have
    to be compiled once more for each new library or executable where
    we declare the use of the precompiled header.

  - Add the Makefile knob NO_PRECOMPILED_HEADER to make it possible to
    build without using the precompiled header for testing purposes,
    or for any compiler that might be out there that doesn't support
    the "-Winvalid-pch" option.

    Note, that when this knob is set then we merely leave
    PRECOMPILED_HEADER_USERS empty: this way nothing is built with the
    precompiled header, but "make clean NO_PRECOMPILED_HEADER=1" would
    still remove a leftover precompiled header file.

With this patch series on top of v2.55.0 I got the following build
time improvement:

  Benchmark 1: make -j12 (rev = v2.55.0)
    Time (mean ± σ):     29.414 s ±  0.031 s    [User: 254.786 s, System: 47.447 s]
    Range (min … max):   29.370 s … 29.470 s    10 runs

  Benchmark 2: make -j12 (rev = precompile)
    Time (mean ± σ):     21.725 s ±  0.047 s    [User: 186.047 s, System: 35.109 s]
    Range (min … max):   21.643 s … 21.768 s    10 runs

  Summary
    'make -j12 (rev = precompile)' ran
      1.35 ± 0.00 times faster than 'make -j12 (rev = v2.55.0)'

[1] "make" applies target-specific variables to the first target's
    dependencies as well.  So, if the rule creating the precompiled
    header included $(EXTRA_CPPFLAGS) as well, then we could get this:

      $ make -s clean
      $ make V=1 git
      gcc -o tools/precompiled.h.gch -c -MF [...] -DSHELL_PATH='"/bin/sh"' '-DGIT_HTML_PATH="share/doc/git-doc"' '-DGIT_MAN_PATH="share/man"' '-DGIT_INFO_PATH="share/info"' tools/precompiled.h
      gcc -o git.o -c -include tools/precompiled.h -Winvalid-pch -MF [...] -DSHELL_PATH='"/bin/sh"' '-DGIT_HTML_PATH="share/doc/git-doc"' '-DGIT_MAN_PATH="share/man"' '-DGIT_INFO_PATH="share/info"' git.c
      gcc -o builtin/add.o -c -include tools/precompiled.h -Winvalid-pch -MF [...] -DSHELL_PATH='"/bin/sh"'  builtin/add.c
      cc1: error: ./tools/precompiled.h.gch: not used because `GIT_MAN_PATH' not defined [-Werror=invalid-pch]
      cc1: all warnings being treated as errors
      make: *** [Makefile:2940: builtin/add.o] Error 1

    So in this case "git.o" is the first object file to be build, and
    since it has a target-specific EXTRA_CPPFLAGS and since it depends
    on the precompiled header, the precompiled header is built with
    the same EXTRA_CPPFLAGS as well.  But then "builtin/add.o" is
    built with empty EXTRA_CPPFLAGS, and GCC's sanity checks for the
    -Winvalid-pch option complain.  Clang apparently doesn't consider
    this to be an issue, and builds "git" just fine.

    Note, however, that if the first object file to be built is not
    "git.o" (or one of the other object files with target-specific
    EXTRA_CPPFLAGS), which is usually the case with e.g. "make all",
    then the precompiled header is built with empty EXTRA_CPPFLAGS,
    and then all is well.  Weird.  We already had issues with "make"
    and target-specific variables in the past, see a673cfede6
    (Makefile: Fix occasional GIT-CFLAGS breakage, 2010-03-19).
    The Meson build doesn't use target-specific variables, and the
    whole project needs to be rebuilt when e.g. "mandir" is changed,
    although this is not mentioned in 904339edbd (Introduce support
    for the Meson build system, 2024-12-06).

[2] See baa61e46da (git-compat-util.h: move warning infra to prepare
    for PCHs, 2026-03-19).

[3] This can be verified by simply scanning through the output of:

    {
            printf '%s\n' 'print-%:'
            printf '\t%s\n' '@printf "%s\n" $($*)'
    } >/tmp/printvars.mak
    for f in $(make -f /tmp/printvars.mak -f Makefile print-PRECOMPILED_HEADER_USERS)
    do
            f="${f%o}c"
            sed -n -E -e "s%# *(define|include).*%&    $f%p" -e '/# *include/q' "$f"
    done | sort

[4] "make"'s flexibility would allow us to separately list those
    object files that don't include "git-compat-util.h", but then on
    my (I assume fairly typical) Linux box the number of object files
    built using the precompiled header increases only by 9 (from 536
    to 545), which reduces the build time by about 1% (0.2s).
    Therefore, I don't think it's worth the churn.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
---
 .gitignore |  1 +
 Makefile   | 26 +++++++++++++++++++++-----
 2 files changed, 22 insertions(+), 5 deletions(-)

diff --git a/.gitignore b/.gitignore
index 4da58c6754..0209bd16f2 100644
--- a/.gitignore
+++ b/.gitignore
@@ -233,6 +233,7 @@
 /.vscode/
 /tags
 /TAGS
+/tools/precompiled.h.gch
 /cscope*
 /compile_commands.json
 /.cache/
diff --git a/Makefile b/Makefile
index 2c4d6f4d4a..02162719db 100644
--- a/Makefile
+++ b/Makefile
@@ -321,6 +321,9 @@ include shared.mak
 # dependency rules.  The default is "auto", which means to use computed header
 # dependencies if your compiler is detected to support it.
 #
+# Define NO_PRECOMPILED_HEADER if you want to build Git without precompiling
+# "git-compat-util.h".
+#
 # Define NATIVE_CRLF if your platform uses CRLF for line endings.
 #
 # Define GIT_USER_AGENT if you want to change how git identifies itself during
@@ -2905,8 +2908,15 @@ endif
 .PHONY: objects
 objects: $(OBJECTS)
 
-dep_files := $(foreach f,$(OBJECTS),$(dir $f).depend/$(notdir $f).d)
-dep_dirs := $(addsuffix .depend,$(sort $(dir $(OBJECTS))))
+PRECOMPILED_HEADER := tools/precompiled.h
+PRECOMPILED_HEADER_GCH := $(addsuffix .gch,$(PRECOMPILED_HEADER))
+
+ifndef NO_PRECOMPILED_HEADER
+PRECOMPILED_HEADER_USERS := $(filter-out $(COMPAT_OBJS) $(REFTABLE_OBJS) $(patsubst %.c,%.o,$(THIRD_PARTY_SOURCES)),$(OBJECTS))
+endif
+
+dep_files := $(foreach f,$(OBJECTS) $(PRECOMPILED_HEADER_GCH),$(dir $f).depend/$(notdir $f).d)
+dep_dirs := $(addsuffix .depend,$(sort $(dir $(OBJECTS) $(PRECOMPILED_HEADER_GCH))))
 
 ifeq ($(uname_S),Darwin)
 	dep_dirs += $(addsuffix .depend,$(sort $(dir contrib/credential/osxkeychain/git-credential-osxkeychain.o)))
@@ -2940,7 +2950,13 @@ missing_compdb_dir =
 compdb_args =
 endif
 
-$(OBJECTS): %.o: %.c GIT-CFLAGS $(missing_dep_dirs) $(missing_compdb_dir)
+$(PRECOMPILED_HEADER_GCH): %.gch: % GIT-CFLAGS $(missing_dep_dirs) $(missing_compdb_dir)
+	$(QUIET_CC)$(CC) -o $@ -c $(dep_args) $(compdb_args) $(ALL_CFLAGS) $<
+
+$(PRECOMPILED_HEADER_USERS): %.o: %.c $(PRECOMPILED_HEADER_GCH) GIT-CFLAGS $(missing_dep_dirs) $(missing_compdb_dir)
+	$(QUIET_CC)$(CC) -o $*.o -c -include $(PRECOMPILED_HEADER) -Winvalid-pch $(dep_args) $(compdb_args) $(ALL_CFLAGS) $(EXTRA_CPPFLAGS) $<
+
+$(filter-out $(PRECOMPILED_HEADER_USERS),$(OBJECTS)): %.o: %.c GIT-CFLAGS $(missing_dep_dirs) $(missing_compdb_dir)
 	$(QUIET_CC)$(CC) -o $*.o -c $(dep_args) $(compdb_args) $(ALL_CFLAGS) $(EXTRA_CPPFLAGS) $<
 
 %.s: %.c GIT-CFLAGS FORCE
@@ -2954,7 +2970,7 @@ ifneq ($(dep_files_present),)
 include $(dep_files_present)
 endif
 else
-$(OBJECTS): $(LIB_H) $(GENERATED_H)
+$(OBJECTS) $(PRECOMPILED_HEADER_GCH): $(LIB_H) $(GENERATED_H)
 endif
 
 ifeq ($(GENERATE_COMPILATION_DATABASE),yes)
@@ -3908,7 +3924,7 @@ clean: profile-clean coverage-clean cocciclean
 	$(RM) GIT-TEST-SUITES
 	$(RM) po/git.pot po/git-core.pot
 	$(RM) git.rc git.res
-	$(RM) $(OBJECTS)
+	$(RM) $(OBJECTS) $(PRECOMPILED_HEADER_GCH)
 	$(RM) headless-git.o
 	$(RM) $(LIB_FILE)
 	$(RM) $(ALL_PROGRAMS) $(SCRIPT_LIB) $(BUILT_INS) $(OTHER_PROGRAMS)
-- 
2.56.0.rc0.467.ge054dd0dd6

Re: [PATCH v2 4/4] Makefile: precompile "git-compat-util.h"

[Jeff King]

On Tue, Sep 15, 2026 at 08:09:52AM +0200, SZEDER Gábor wrote:

> This patch follows the idea of 671df48df8 (meson: precompile
> "git-compat-util.h", 2026-03-19) to make it faster to build Git using
> "make".  The notable differences are the boilerplate needed to wire up
> the precompiled header with "make", and the selection of object files
> that are built using the precompiled header:

I got an interesting error message from this today:

  $ make imap-send.o
      * new build flags
      CC tools/precompiled.h.gch
      CC imap-send.o
  cc1: warning: ./tools/precompiled.h.gch: not used because ‘NO_OPENSSL’ is defined [-Winvalid-pch]

You won't see it with:

  make NO_OPENSSL=1 imap-send.o

The culprit is that I have this in my config.mak:

  imap-send.o: EXTRA_CPPFLAGS += -DNO_OPENSSL

so the build options for the precompiled header and imap-send.c are not
the same. So now of course you are asking why I would have such a weird
line in my config.mak.

The answer is that I want to disable openssl for old builds, because I
am often building historical versions which use openssl constructs that
are deprecated or removed. So naturally you are now asking why it does
not just say:

  NO_OPENSSL = BrokenOnOldVersions

or similar. But that breaks _some_ old versions which really do need
openssl for various things.

The good-ish news is that it's mostly cosmetic for me. I also loosen
-Werror for old builds, for obvious reasons. So it's not breaking any
build.

I don't know if my use case is too crazy to care about, but I thought
I'd mention it in case there are other less-crazy related cases we might
run into.

And yes, obviously old versions will not have the precompiled header,
either, but my logic for "loosen compilation" is mostly "we are not on a
branch nor rebasing", so a sight-seeing trip to "git checkout
origin/seen" puts me in the same mode. And eventually it _will_ be old,
too. ;)

-Peff

Re: [PATCH v2 4/4] Makefile: precompile "git-compat-util.h"

[SZEDER Gábor]

On Thu, Sep 24, 2026 at 07:52:16PM -0400, Jeff King wrote:
> On Tue, Sep 15, 2026 at 08:09:52AM +0200, SZEDER Gábor wrote:
> 
> > This patch follows the idea of 671df48df8 (meson: precompile
> > "git-compat-util.h", 2026-03-19) to make it faster to build Git using
> > "make".  The notable differences are the boilerplate needed to wire up
> > the precompiled header with "make", and the selection of object files
> > that are built using the precompiled header:
> 
> I got an interesting error message from this today:
> 
>   $ make imap-send.o
>       * new build flags
>       CC tools/precompiled.h.gch
>       CC imap-send.o
>   cc1: warning: ./tools/precompiled.h.gch: not used because ‘NO_OPENSSL’ is defined [-Winvalid-pch]
> 
> You won't see it with:
> 
>   make NO_OPENSSL=1 imap-send.o
> 
> The culprit is that I have this in my config.mak:
> 
>   imap-send.o: EXTRA_CPPFLAGS += -DNO_OPENSSL
> 
> so the build options for the precompiled header and imap-send.c are not
> the same.

Hrm.  I've run into this with 'make git.o' and the other object files
for which we set EXTRA_CPPFLAGS in our Makefile, and wrote about it at
length in the commit message.  I thought omitting EXTRA_CPPFLAGS from
the command building the precompiled header solved this issue, and was
puzzled at first why your use case still causes problems...  The
reason for the difference is that none of the EXTRA_CPPFLAGS we set in
our Makefile affect 'git-compat-util.h', but -DNO_OPENSSL does.

If you set such a custom EXTRA_CPPFLAGS, then you might as well append
'-Wno-invalid-pch' to it to silence that warning.  The rule building
object files using the precompiled header has '-Winvalid-pch' near the
beginning while EXTRA_CPPFLAGS are near the end, so we can override it
from EXTRA_CPPFLAGS.  I didn't find a way to override '-include
precompiled.h'.

(Btw, can you do something like this with Meson? :) Without resorting
to creating yet another static library, of course.)

> So now of course you are asking why I would have such a weird
> line in my config.mak.
> 
> The answer is that I want to disable openssl for old builds, because I
> am often building historical versions which use openssl constructs that
> are deprecated or removed.

Well, for the same reason I have the following in my config.mak:

  # Build knobs to build older versions:
  # 1ed2c7b115 (imap-send: use HMAC() function provided by OpenSSL, 2016-04-09)
  ifeq ($(shell git merge-base --is-ancestor 1ed2c7b11570f5d16bdc70d151fa78c3dccf6d38 HEAD 2>/dev/null; echo $$?),1)
    $(warning Setting NO_OPENSSL for old revisions)
    NO_OPENSSL = UnfortunatelyYes
  endif

> So naturally you are now asking why it does
> not just say:
> 
>   NO_OPENSSL = BrokenOnOldVersions
> 
> or similar. But that breaks _some_ old versions which really do need
> openssl for various things.

I haven't run into any such breakages with disabling OPENSSL for the
whole build... but maybe I just haven't built old enough versions?!
Anyway, will adapt it to your EXTRA_CPPFLAGS trick, thanks.

> The good-ish news is that it's mostly cosmetic for me. I also loosen
> -Werror for old builds, for obvious reasons. So it's not breaking any
> build.
> 
> I don't know if my use case is too crazy to care about

I would say so, yes ;)

> but I thought
> I'd mention it in case there are other less-crazy related cases we might
> run into.

Not sure what those less crazy use cases might be, but I'm inclined to
say that "If you deliberately set a custom EXTRA_CPPFLAGS that affects
'git-compat-util.h', then you should also add '-Wno-invalid-pch' as
well".

> And yes, obviously old versions will not have the precompiled header,
> either, but my logic for "loosen compilation" is mostly "we are not on a
> branch nor rebasing", so a sight-seeing trip to "git checkout
> origin/seen" puts me in the same mode. And eventually it _will_ be old,
> too. ;)

I'm not sure about loosening compilation for 'seen', especially when
it comes to DEVELOPER=1, because it's best to catch any issues with
DEVELOPER=1 while the commit is still only in 'seen'.  My config.mak
doesn't set DEVELOPER=1 when bisecting or when building a revision
reachable from a tagged release.

Re: [PATCH v2 4/4] Makefile: precompile "git-compat-util.h"

[SZEDER Gábor]

On Tue, Sep 15, 2026 at 08:09:52AM +0200, SZEDER Gábor wrote:
>     - The precompiled header should not change what actually gets
>       compiled.  Therefore, use the precompiled header only when
>       compiling source files that start with including
>       "git-compat-util.h" (directly or indirectly, e.g. via
>       "builtin.h"), or its inclusion is only preceeded by #define
>       directives that don't influence "git-compat-util.h" between its
>       include guards [2] (currently DISABLE_SIGN_COMPARE_WARNINGS,
>       USE_THE_REPOSITORY_VARIABLE or GIT_TEST_PROGRESS_ONLY). [3]

Well, it turns out the precompiled header does change what gets
compiled, and it causes a visible behavior difference, though I think
it's really minor.

The crux of the issue is that without the precompiled header the
compiler processes "git-compat-util.h", but with it, for some reason,
it processes "./git-compat-util.h".

This is visible when expanding __FILE__ in "git-compat-util.h", e.g.
in the assert macro in regexec_buf().  When the assertion is
triggered, e.g. with this diff:

diff --git a/common-main.c b/common-main.c
index 6b7ab077b0..dd2a90c849 100644
--- a/common-main.c
+++ b/common-main.c
@@ -5,6 +5,9 @@ int main(int argc, const char **argv)
 {
 	int result;
 
+	/* Intentionally bogus regexec_buf() call to trigger its assert() */
+	regexec_buf(NULL, NULL, 0, 0, NULL, 0);
+
 	init_git(argv);
 	result = cmd_main(argc, argv);
 
Then without the precompiled header we get:

  $ ./git
  git: git-compat-util.h:1002: regexec_buf: Assertion `nmatch > 0 && pmatch' failed.
  Aborted (core dumped)

But with the precompiled header:

  $ ./git
  git: ./git-compat-util.h:1002: regexec_buf: Assertion `nmatch > 0 && pmatch' failed.
  Aborted (core dumped)

Similar could happen when the ALLOC_GROW_BY() macro is invoked with
bogus parameters to trigger a BUG().

(Sidenote: While this assert does prevent us from invoking regexec()
with nonsense, the source file name and line number in the resulting
error message are not as useful as they could be, it would be better
to show the caller's filename and line number.)

Since in "git-compat-util.h" __FILE__ is only expanded in error
messages that should basically never happen (BUG() and assert()), I
think this is acceptable.


BTW, this is also visible in compiler error messages:

diff --git a/git-compat-util.h b/git-compat-util.h
index a0f901ce79..00c1f26911 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -1,6 +1,8 @@
 #ifndef GIT_COMPAT_UTIL_H
 #define GIT_COMPAT_UTIL_H
 
+trigger_compiler_error
+
 #if __STDC_VERSION__ - 0 < 199901L
 /*
  * Git is in a testing period for mandatory C99 support in the compiler.  If

Without precompiled header:

      CC daemon.o
  In file included from daemon.c:3:
  git-compat-util.h:4:23: error: expected ‘;’ before ‘typedef’
      4 | trigger_compiler_error
        |                       ^
        |                       ;

With precompiled header:

      CC tools/precompiled.h.gch
  In file included from tools/precompiled.h:1:
  ./git-compat-util.h:4:23: error: expected ‘;’ before ‘typedef’
      4 | trigger_compiler_error
        |                       ^
        |                       ;