https://gcc.gnu.org/g:1c68b2b4e244dff5f1087c37a68dd891ffae58b4
commit r16-7448-g1c68b2b4e244dff5f1087c37a68dd891ffae58b4 Author: Jakub Jelinek <[email protected]> Date: Wed Feb 11 11:34:09 2026 +0100 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 <[email protected]> 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: --- gcc/cfgexpand.cc | 15 +++++--- gcc/testsuite/gcc.target/i386/pr124056.c | 61 ++++++++++++++++++++++++++++++++ 2 files changed, 72 insertions(+), 4 deletions(-) diff --git a/gcc/cfgexpand.cc b/gcc/cfgexpand.cc index 02f4c272c675..7517e8d57889 100644 --- 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 index 000000000000..5f646f7914e5 --- /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 (); +}
