https://gcc.gnu.org/g:e82c8413eda498163ae2e0ecc458ea0428708c30
commit r16-3163-ge82c8413eda498163ae2e0ecc458ea0428708c30
Author: Richard Sandiford <richard.sandif...@arm.com>
Date: Tue Aug 12 10:21:47 2025 +0100
fwprop: Don't propagate asms [PR121253]
For the reasons explained in the comment, fwprop shouldn't even
try to propagate an asm definition.
gcc/
PR rtl-optimization/121253
* fwprop.cc (forward_propagate_into): Don't propagate asm defs.
gcc/testsuite/
PR rtl-optimization/121253
* gcc.target/aarch64/pr121253.c: New test.
Diff:
---
gcc/fwprop.cc | 14 ++++++++++++++
gcc/testsuite/gcc.target/aarch64/pr121253.c | 16 ++++++++++++++++
2 files changed, 30 insertions(+)
diff --git a/gcc/fwprop.cc b/gcc/fwprop.cc
index 4ee44adcde29..59df7cad0dee 100644
--- a/gcc/fwprop.cc
+++ b/gcc/fwprop.cc
@@ -836,6 +836,20 @@ forward_propagate_into (use_info *use, bool reg_prop_only
= false)
if (def_insn->is_artificial ())
return false;
+ /* Do not propagate asms. The only kind of propagation that would
+ succeed is propagation into a register move. Such a propagation
+ is neutral if the destination of the move is a pseudo and unnecessarily
+ restricts the register allocator if the destination of the move is
+ a hard register.
+
+ Furthermore, unlike for a normal instruction, we cannot take a SET from an
+ asm and try dropping the CLOBBERs. The recog process does not (and should
+ not try to) second-guess whether what the user wrote can be changed and
+ so it has to assume that any asm given to it is a fair reflection of
+ what the user wrote. */
+ if (def_insn->is_asm ())
+ return false;
+
rtx_insn *def_rtl = def_insn->rtl ();
if (!NONJUMP_INSN_P (def_rtl))
return false;
diff --git a/gcc/testsuite/gcc.target/aarch64/pr121253.c
b/gcc/testsuite/gcc.target/aarch64/pr121253.c
new file mode 100644
index 000000000000..37de605c6462
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/pr121253.c
@@ -0,0 +1,16 @@
+/* { dg-options "-O" } */
+
+struct s128 {
+ long a, b;
+};
+
+struct s128 foo(void) {
+ struct s128 ret;
+ asm("mov %0, #0 \n\t"
+ "mov %R0, #0 \n\t"
+ "mov x0, #12345"
+ : "=r" (ret) : : "x0");
+ return ret;
+}
+
+/* { dg-final { scan-assembler-not {mov x0, #0} } } */
