From: Andrew Pinski <andrew.pinski@oss.qualcomm.com>
Date: Tue, 14 Oct 2025 16:13:51 +0000 (-0700)
Subject: dce: Remove __builtin_stack_save during dce [PR122037]
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=94ce59ad335ac372afb4521e880add4cf8fc0607;p=thirdparty%2Fgcc.git

dce: Remove __builtin_stack_save during dce [PR122037]

__builtin_stack_save can be removed when the lhs becomes unused
as it is just recording the current StackPointer into another register.

Bootstrapped and tested on x86_64-linux-gnu.

	PR tree-optimization/122037

gcc/ChangeLog:

	* tree-ssa-dce.cc (eliminate_unnecessary_stmts): Remove
	__builtin_stack_save when the lhs is unused.

gcc/testsuite/ChangeLog:

	* gcc.dg/tree-ssa/vla-1.c: New test.

Signed-off-by: Andrew Pinski <andrew.pinski@oss.qualcomm.com>
---

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/vla-1.c b/gcc/testsuite/gcc.dg/tree-ssa/vla-1.c
new file mode 100644
index 00000000000..37b75142407
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/vla-1.c
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized -fdump-tree-cddce1-details" } */
+/* PR tree-optimization/122037 */
+
+void bar1 (char *, int) __attribute__((noreturn));
+void foo1 (int size)
+{
+  char temp[size];
+  temp[size-1] = '\0';
+  bar1 (temp, size);
+}
+
+/* The call to __builtin_stack_save should have been removed. */
+/* { dg-final { scan-tree-dump "Deleting : __builtin_stack_save" "cddce1" } } */
+/* { dg-final { scan-tree-dump-not "__builtin_stack_save " "optimized" } } */
diff --git a/gcc/tree-ssa-dce.cc b/gcc/tree-ssa-dce.cc
index 43869088322..160c28cb807 100644
--- a/gcc/tree-ssa-dce.cc
+++ b/gcc/tree-ssa-dce.cc
@@ -1682,9 +1682,12 @@ eliminate_unnecessary_stmts (bool aggressive)
 		  update_stmt (call_stmt);
 		  release_ssa_name (name);
 
+		  /* __builtin_stack_save without lhs is not needed.  */
+		  if (gimple_call_builtin_p (call_stmt, BUILT_IN_STACK_SAVE))
+		    remove_dead_stmt (&gsi, bb, to_remove_edges);
 		  /* GOMP_SIMD_LANE (unless three argument) or ASAN_POISON
 		     without lhs is not needed.  */
-		  if (gimple_call_internal_p (call_stmt))
+		  else if (gimple_call_internal_p (call_stmt))
 		    switch (gimple_call_internal_fn (call_stmt))
 		      {
 		      case IFN_GOMP_SIMD_LANE: