ifcvt: do not emit a store flag for an irreversible condition [PR126347]

noce_emit_store_flag feeds the possibly-reversed comparison code to a
store-flag insn, and to emit_store_flag, without checking that the
reversal succeeded.  reversed_comparison_code returns UNKNOWN for
UNLT/UNLE/UNGT/UNGE, and for a MODE_CC comparison it cannot trace back
to its COMPARE -- common for a floating-point condition on targets that
compare into a condition-code register.  emit_store_flag then reaches
its floating-point path and calls swap_condition (UNKNOWN), which aborts.

This was latent until r17-2519-ga33f26607eb4f3 made
noce_try_shifted_store_flag the first caller to reach
noce_emit_store_flag with REVERSEP set for such a condition.

Bail out early when the reversal failed.

Bootstrapped and regression tested on aarch64-unknown-linux-gnu with no
regressions.

	PR rtl-optimization/126347
gcc/
	* ifcvt.cc (noce_emit_store_flag): Return NULL_RTX when the
	comparison code is UNKNOWN.

diff --git a/gcc/ifcvt.cc b/gcc/ifcvt.cc
index 7c50ab06e2f7369e6f9b11c83529b5afbab8b025..6b169e69741dd82466264063ee0ce89be421f54b 100644 (file)
--- a/gcc/ifcvt.cc
+++ b/gcc/ifcvt.cc
@@ -865,6 +865,11 @@ noce_emit_store_flag (struct noce_if_info *if_info, rtx x, bool reversep,
   else
     code = GET_CODE (cond);
 
+  /* reversed_comparison_code returns UNKNOWN for an unordered code, or a
+     CC-mode compare it cannot trace; neither path below can use that.  */
+  if (code == UNKNOWN)
+    return NULL_RTX;
+
   if ((if_info->cond_earliest == if_info->jump || cond_complex)
       && (normalize == 0 || STORE_FLAG_VALUE == normalize))
     {