cfgexpand: Fix up "=@ccz" etc. outputs on asm goto [PR124056]

The following testcase is miscompiled, because after_md_seq which is
what is emitted for "=@cc?" outputs to initialize a pseudo with
the result is emitted just once, on the asm goto fallthru edge, before
after_rtl_seq (on that edge that is the correct ordering), but a copy
of after_rtl_seq is also emitted on the other edges from asm goto, but
after_md_seq is not.
So, the pseudo with the flags checking is initialized only in the
fallthru case and not when asm goto is left through one of the other
labels (unless those are degenerate).

The following patch arranges to emit that sequence duplicated on all the
edges before after_rtl_seq sequence, by modifying after_rtl_seq so that
it includes after_md_seq followed by the old after_rtl_seq.

2026-02-11  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/124056
	* cfgexpand.cc (expand_asm_stmt): If after_md_seq is non-NULL, emit
	it at the start of after_rtl_seq instead of after fallthru_label.

	* gcc.target/i386/pr124056.c: New test.

diff --git a/gcc/cfgexpand.cc b/gcc/cfgexpand.cc
index 02f4c272c675605e6049eba113ad6c36af8ecfa2..7517e8d57889644392b1f7760face596c80ef221 100644 (file)
--- a/gcc/cfgexpand.cc
+++ b/gcc/cfgexpand.cc
@@ -3786,13 +3786,22 @@ expand_asm_stmt (gasm *stmt)
      Case in point is when the i386 backend moved from cc0 to a hard reg --
      maintaining source-level compatibility means automatically clobbering
      the flags register.  */
-  rtx_insn *after_md_seq = NULL;
   auto_vec<rtx> use_rvec;
   if (targetm.md_asm_adjust)
-    after_md_seq
+    {
+      rtx_insn *after_md_seq
        = targetm.md_asm_adjust (output_rvec, input_rvec, input_mode,
                                 constraints, use_rvec, clobber_rvec,
                                 clobbered_regs, locus);
+      if (after_md_seq)
+       {
+         push_to_sequence (after_md_seq);
+         emit_insn (after_rtl_seq);
+         after_rtl_seq = get_insns ();
+         after_rtl_end = get_last_insn ();
+         end_sequence ();
+       }
+    }
 
   /* Do not allow the hook to change the output and input count,
      lest it mess up the operand numbering.  */
@@ -3967,8 +3976,6 @@ expand_asm_stmt (gasm *stmt)
   if (fallthru_label)
     emit_label (fallthru_label);
 
-  if (after_md_seq)
-    emit_insn (after_md_seq);
   if (after_rtl_seq)
     {
       if (nlabels == 0)

diff --git a/gcc/testsuite/gcc.target/i386/pr124056.c b/gcc/testsuite/gcc.target/i386/pr124056.c
new file mode 100644 (file)
index 0000000..5f646f7
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr124056.c
@@ -0,0 +1,61 @@
+/* PR middle-end/124056 */
+/* { dg-do run } */
+/* { dg-options "-O2 -masm=att" } */
+
+int v;
+
+[[gnu::noipa]] void
+foo (void)
+{
+  v = 42;
+}
+
+[[gnu::noipa]] void
+bar (void)
+{
+  v = 43;
+}
+
+[[gnu::noipa]] int
+baz (void)
+{
+  bool err;
+  __asm goto ("movl %1, %%ecx\n\t"
+              "test %%ecx, %%ecx\n\t"
+              "js 1f\n\t"
+              "jmp %l[lab]\n\t"
+           "1: cmpl $-1, %%ecx"
+              : "=@ccz" (err) : "m" (v) : "ecx" : lab);
+  if (err)
+    {
+      bar ();
+      return -1;
+    }
+  return 0;
+
+ lab:
+  if (err)
+    {
+      foo ();
+      return -2;
+    }
+
+  return 1;
+}
+
+int
+main ()
+{
+  v = 0;
+  if (baz () != -2 || v != 42)
+    __builtin_abort ();
+  v = 1;
+  if (baz () != 1 || v != 1)
+    __builtin_abort ();
+  v = -1;
+  if (baz () != -1 || v != 43)
+    __builtin_abort ();
+  v = -2;
+  if (baz () != 0 || v != -2)
+    __builtin_abort ();
+}