[styhead][PATCH] Backport: Fix c++: tweak for Wrange-loop-construct

[sunilkumar.dora@windriver.com]

From: Sunil Dora <sunilkumar.dora@windriver.com>

This commit updates the warning to use a check for "trivially constructible" instead of
"trivially copyable." The original check was incorrect, as "trivially copyable" only applies
to types that can be copied trivially, whereas "trivially constructible" is the correct check
for types that can be trivially default-constructed.

This change ensures the warning is more accurate and aligns with the proper type traits.

LLVM accepted a similar fix:
https://github.com/llvm/llvm-project/issues/47355

PR c++/116731 [https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116731]

Upstream-Status: Backport [https://gcc.gnu.org/g:6ac4e2f4b2ca9980670e7d3815a9140730df1005]

Signed-off-by: Marek Polacek <polacek@redhat.com>
Signed-off-by: Sunil Dora <sunilkumar.dora@windriver.com>
---
 meta/recipes-devtools/gcc/gcc-14.2.inc        |   1 +
 ...ix-c-tweak-for-Wrange-loop-construct.patch | 114 ++++++++++++++++++
 2 files changed, 115 insertions(+)
 create mode 100644 meta/recipes-devtools/gcc/gcc/0026-Backport-Fix-c-tweak-for-Wrange-loop-construct.patch

diff --git a/meta/recipes-devtools/gcc/gcc-14.2.inc b/meta/recipes-devtools/gcc/gcc-14.2.inc
index e90b5b4c2a..1378cfc1c3 100644
--- a/meta/recipes-devtools/gcc/gcc-14.2.inc
+++ b/meta/recipes-devtools/gcc/gcc-14.2.inc
@@ -68,6 +68,7 @@ SRC_URI = "${BASEURI} \
            file://0023-Fix-install-path-of-linux64.h.patch \
            file://0024-Avoid-hardcoded-build-paths-into-ppc-libgcc.patch \
            file://0025-gcc-testsuite-tweaks-for-mips-OE.patch \
+	   file://0026-Backport-Fix-c-tweak-for-Wrange-loop-construct.patch \
            file://gcc.git-ab884fffe3fc82a710bea66ad651720d71c938b8.patch \
 "
 
diff --git a/meta/recipes-devtools/gcc/gcc/0026-Backport-Fix-c-tweak-for-Wrange-loop-construct.patch b/meta/recipes-devtools/gcc/gcc/0026-Backport-Fix-c-tweak-for-Wrange-loop-construct.patch
new file mode 100644
index 0000000000..0a2db4e36a
--- /dev/null
+++ b/meta/recipes-devtools/gcc/gcc/0026-Backport-Fix-c-tweak-for-Wrange-loop-construct.patch
@@ -0,0 +1,114 @@
+From acc5e13c2ea91d2a138c03cd9e5d8826a1a74e4d Mon Sep 17 00:00:00 2001
+From: Sunil Dora <sunilkumar.dora@windriver.com>
+Date: Wed, 11 Dec 2024 00:09:43 -0800
+Subject: [PATCH] Backport: Fix c++: tweak for Wrange-loop-construct
+
+This commit updates the warning to use a check for "trivially constructible" instead of 
+"trivially copyable." The original check was incorrect, as "trivially copyable" only applies 
+to types that can be copied trivially, whereas "trivially constructible" is the correct check 
+for types that can be trivially default-constructed. 
+
+This change ensures the warning is more accurate and aligns with the proper type traits.
+
+LLVM accepted a similar fix:
+https://github.com/llvm/llvm-project/issues/47355
+
+PR c++/116731 [https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116731]
+
+Upstream-Status: Backport [https://gcc.gnu.org/g:6ac4e2f4b2ca9980670e7d3815a9140730df1005]
+
+Signed-off-by: Marek Polacek <polacek@redhat.com>
+Signed-off-by: Sunil Dora <sunilkumar.dora@windriver.com>
+---
+ gcc/cp/parser.cc                              |  8 ++-
+ .../g++.dg/warn/Wrange-loop-construct3.C      | 57 +++++++++++++++++++
+ 2 files changed, 62 insertions(+), 3 deletions(-)
+ create mode 100644 gcc/testsuite/g++.dg/warn/Wrange-loop-construct3.C
+
+diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
+index 7e81c1010..8206489a2 100644
+--- a/gcc/cp/parser.cc
++++ b/gcc/cp/parser.cc
+@@ -14301,11 +14301,13 @@ warn_for_range_copy (tree decl, tree expr)
+   else if (!CP_TYPE_CONST_P (type))
+     return;
+ 
+-  /* Since small trivially copyable types are cheap to copy, we suppress the
+-     warning for them.  64B is a common size of a cache line.  */
++  /* Since small trivially constructible types are cheap to construct, we 
++     suppress the warning for them.  64B is a common size of a cache line.  */
++  tree vec = make_tree_vec (1);
++  TREE_VEC_ELT (vec, 0) = TREE_TYPE (expr);
+   if (TREE_CODE (TYPE_SIZE_UNIT (type)) != INTEGER_CST
+       || (tree_to_uhwi (TYPE_SIZE_UNIT (type)) <= 64
+-	  && trivially_copyable_p (type)))
++	  && is_trivially_xible (INIT_EXPR, type, vec)))
+     return;
+ 
+   /* If we can initialize a reference directly, suggest that to avoid the
+diff --git a/gcc/testsuite/g++.dg/warn/Wrange-loop-construct3.C b/gcc/testsuite/g++.dg/warn/Wrange-loop-construct3.C
+new file mode 100644
+index 000000000..3d9d0c908
+--- /dev/null
++++ b/gcc/testsuite/g++.dg/warn/Wrange-loop-construct3.C
+@@ -0,0 +1,57 @@
++// PR c++/116731
++// { dg-do compile { target c++11 } }
++// { dg-options "-Wrange-loop-construct" }
++
++void
++f0 ()
++{
++  struct S {
++    char a[64];
++    S& operator=(const S&) { return *this; };
++  };
++
++  S arr[8];
++  for (const auto r : arr)
++    (void) r;
++}
++
++void
++f1 ()
++{
++  struct S {
++    char a[65];
++    S& operator=(const S&) { return *this; };
++  };
++
++  S arr[8];
++  for (const auto r : arr) // { dg-warning "creates a copy" }
++    (void) r;
++}
++
++void
++f2 ()
++{
++  struct S {
++    char a[64];
++    S& operator=(const S&) { return *this; };
++    ~S() { }
++  };
++
++  S arr[8];
++  for (const auto r : arr) // { dg-warning "creates a copy" }
++    (void) r;
++}
++
++void
++f3 ()
++{
++  struct S {
++    char a[65];
++    S& operator=(const S&) { return *this; };
++    ~S() { }
++  };
++
++  S arr[8];
++  for (const auto r : arr) // { dg-warning "creates a copy" }
++    (void) r;
++}
+-- 
+2.43.0
+
-- 
2.43.0