[PATCH v4 6/9] perf dwarf-aux: Skip check_variable for die_find_variable_by_reg

[Zecheng Li <zecheng@google.com>]

In die_find_variable_by_reg, match_var_offset already performs
sufficient checking and type matching. The additional check_variable
call is redundant, and its need_pointer logic is only a heuristic. Since
DWARF encodes accurate type information, which match_var_offset
verifies, skipping check_variable improves both coverage and accuracy.

Return type from die_find_variable_by_reg via a new `type` field in
find_var_data.

Signed-off-by: Zecheng Li <zecheng@google.com>
---
 tools/perf/util/annotate-data.c |  8 +++++---
 tools/perf/util/dwarf-aux.c     | 18 +++++++++++-------
 tools/perf/util/dwarf-aux.h     |  2 +-
 3 files changed, 17 insertions(+), 11 deletions(-)

diff --git a/tools/perf/util/annotate-data.c b/tools/perf/util/annotate-data.c
index e183c6104d59..4b08331b9dd3 100644
--- a/tools/perf/util/annotate-data.c
+++ b/tools/perf/util/annotate-data.c
@@ -1603,19 +1603,21 @@ static int find_data_type_die(struct data_loc_info *dloc, Dwarf_Die *type_die)
 			if (!die_find_variable_by_addr(&scopes[i], dloc->var_addr,
 						       &var_die, &type_offset))
 				continue;
+			/* Found a variable, see if it's correct */
+			result = check_variable(dloc, &var_die, &mem_die, reg,
+						type_offset, is_fbreg);
 		} else {
 			/* Look up variables/parameters in this scope */
 			if (!die_find_variable_by_reg(&scopes[i], pc, reg,
-						      &type_offset, is_fbreg, &var_die))
+						      &mem_die, &type_offset, is_fbreg, &var_die))
 				continue;
+			result = PERF_TMR_OK;
 		}
 
 		pr_debug_dtp("found \"%s\" (die: %#lx) in scope=%d/%d (die: %#lx) ",
 			     dwarf_diename(&var_die), (long)dwarf_dieoffset(&var_die),
 			     i+1, nr_scopes, (long)dwarf_dieoffset(&scopes[i]));
 
-		/* Found a variable, see if it's correct */
-		result = check_variable(dloc, &var_die, &mem_die, reg, type_offset, is_fbreg);
 		if (result == PERF_TMR_OK) {
 			if (reg == DWARF_REG_PC) {
 				pr_debug_dtp("addr=%#"PRIx64" type_offset=%#x\n",
diff --git a/tools/perf/util/dwarf-aux.c b/tools/perf/util/dwarf-aux.c
index 9267af204c7d..b57cdc8860f0 100644
--- a/tools/perf/util/dwarf-aux.c
+++ b/tools/perf/util/dwarf-aux.c
@@ -1378,6 +1378,8 @@ struct find_var_data {
 	Dwarf_Addr addr;
 	/* Target register */
 	unsigned reg;
+	/* Access data type */
+	Dwarf_Die type;
 	/* Access offset, set for global data */
 	int offset;
 	/* True if the current register is the frame base */
@@ -1390,7 +1392,6 @@ struct find_var_data {
 static bool match_var_offset(Dwarf_Die *die_mem, struct find_var_data *data,
 			     s64 addr_offset, s64 addr_type, bool is_pointer)
 {
-	Dwarf_Die type_die;
 	Dwarf_Word size;
 	s64 offset = addr_offset - addr_type;
 
@@ -1403,16 +1404,16 @@ static bool match_var_offset(Dwarf_Die *die_mem, struct find_var_data *data,
 	if (offset < 0)
 		return false;
 
-	if (die_get_real_type(die_mem, &type_die) == NULL)
+	if (die_get_real_type(die_mem, &data->type) == NULL)
 		return false;
 
-	if (is_pointer && dwarf_tag(&type_die) == DW_TAG_pointer_type) {
+	if (is_pointer && dwarf_tag(&data->type) == DW_TAG_pointer_type) {
 		/* Get the target type of the pointer */
-		if (die_get_real_type(&type_die, &type_die) == NULL)
+		if (die_get_real_type(&data->type, &data->type) == NULL)
 			return false;
 	}
 
-	if (dwarf_aggregate_size(&type_die, &size) < 0)
+	if (dwarf_aggregate_size(&data->type, &size) < 0)
 		return false;
 
 	if ((u64)offset >= size)
@@ -1529,7 +1530,7 @@ static int __die_find_var_reg_cb(Dwarf_Die *die_mem, void *arg)
  * when the variable is in the stack.
  */
 Dwarf_Die *die_find_variable_by_reg(Dwarf_Die *sc_die, Dwarf_Addr pc, int reg,
-				    int *poffset, bool is_fbreg,
+				    Dwarf_Die *type_die, int *poffset, bool is_fbreg,
 				    Dwarf_Die *die_mem)
 {
 	struct find_var_data data = {
@@ -1541,8 +1542,11 @@ Dwarf_Die *die_find_variable_by_reg(Dwarf_Die *sc_die, Dwarf_Addr pc, int reg,
 	Dwarf_Die *result;
 
 	result = die_find_child(sc_die, __die_find_var_reg_cb, &data, die_mem);
-	if (result)
+	if (result) {
 		*poffset = data.offset;
+		*type_die = data.type;
+	}
+
 	return result;
 }
 
diff --git a/tools/perf/util/dwarf-aux.h b/tools/perf/util/dwarf-aux.h
index cd481ec9c5a1..b3ee5df0b6be 100644
--- a/tools/perf/util/dwarf-aux.h
+++ b/tools/perf/util/dwarf-aux.h
@@ -163,7 +163,7 @@ int die_get_var_range(Dwarf_Die *sp_die, Dwarf_Die *vr_die, struct strbuf *buf);
 
 /* Find a variable saved in the 'reg' at given address */
 Dwarf_Die *die_find_variable_by_reg(Dwarf_Die *sc_die, Dwarf_Addr pc, int reg,
-				    int *poffset, bool is_fbreg,
+				    Dwarf_Die *type_die, int *poffset, bool is_fbreg,
 				    Dwarf_Die *die_mem);
 
 /* Find a (global) variable located in the 'addr' */
-- 
2.51.0.788.g6d19910ace-goog