[gcc r15-76] PHIOPT: Value-replacement check undef

[gcc r15-76] PHIOPT: Value-replacement check undef

[Andrew Pinski]

https://gcc.gnu.org/g:a30d2e6bd0b965e7687f58530a767a3c3b079158

commit r15-76-ga30d2e6bd0b965e7687f58530a767a3c3b079158
Author: Andrew Pinski <quic_apinski@quicinc.com>
Date:   Sun Apr 28 20:21:02 2024 -0700

    PHIOPT: Value-replacement check undef
    
    While moving value replacement part of PHIOPT over
    to use match-and-simplify, I ran into the case where
    we would have an undef use that was conditional become
    unconditional. This prevents that. I can't remember at this
    point what the testcase was though.
    
    Bootstrapped and tested on x86_64-linux-gnu with no regressions.
    
    gcc/ChangeLog:
    
            * tree-ssa-phiopt.cc (value_replacement): Reject undef variables
            so they don't become unconditional used.
    
    Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>

Diff:
---
 gcc/tree-ssa-phiopt.cc | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/gcc/tree-ssa-phiopt.cc b/gcc/tree-ssa-phiopt.cc
index a2bdcb5eae8..f166c3132cb 100644
--- a/gcc/tree-ssa-phiopt.cc
+++ b/gcc/tree-ssa-phiopt.cc
@@ -1146,6 +1146,13 @@ value_replacement (basic_block cond_bb, basic_block middle_bb,
   if (code != NE_EXPR && code != EQ_EXPR)
     return 0;
 
+  /* Do not make conditional undefs unconditional.  */
+  if ((TREE_CODE (arg0) == SSA_NAME
+       && ssa_name_maybe_undef_p (arg0))
+      || (TREE_CODE (arg1) == SSA_NAME
+	  && ssa_name_maybe_undef_p (arg1)))
+    return false;
+
   /* If the type says honor signed zeros we cannot do this
      optimization.  */
   if (HONOR_SIGNED_ZEROS (arg1))