commit ecf19b6eb6f8e17d8d148e3c6627bd2151766420
Author: Andrew MacLeod <amacleod@redhat.com>
Date:   Fri Dec 16 16:53:31 2022 -0500

    Don't use PHI equivalences in range-on-entry.
    
    If there is only one argument to a PHI which is defined, an equivalency is
    created between the def and the argument.  It is safe to consider the def
    equal to the argument, but it is dangerous to assume the argument is also
    equivalent to the def as there may be branches which change the range on the
    path to the PHI on that argument
    
    This patch avoid using that relation in range-on-entry calculations.
    
            PR tree-optimization/108139
            gcc/
            * gimple-range-cache.cc (ranger_cache::fill_block_cache): Do not
            use equivalences originating from PHIS.
    
            gcc/testsuite/
            * gcc.dg/pr108139.c: New.

diff --git a/gcc/gimple-range-cache.cc b/gcc/gimple-range-cache.cc
index ce5a0c8155e..9848d140242 100644
--- a/gcc/gimple-range-cache.cc
+++ b/gcc/gimple-range-cache.cc
@@ -1235,6 +1235,13 @@ ranger_cache::fill_block_cache (tree name, basic_block bb, basic_block def_bb)
 	      if (!m_gori.has_edge_range_p (equiv_name))
 		continue;
 
+	      // PR 108139. It is hazardous to assume an equivalence with
+	      // a PHI is the same value.  The PHI may be an equivalence
+	      // via UNDEFINED arguments which is really a one way equivalence.
+	      // PHIDEF == name, but name may not be == PHIDEF.
+	      if (is_a<gphi *> (SSA_NAME_DEF_STMT (equiv_name)))
+		continue;
+
 	      // Check if the equiv definition dominates this block
 	      if (equiv_bb == bb ||
 		  (equiv_bb && !dominated_by_p (CDI_DOMINATORS, bb, equiv_bb)))
diff --git a/gcc/testsuite/gcc.dg/pr108139.c b/gcc/testsuite/gcc.dg/pr108139.c
new file mode 100644
index 00000000000..6f224e3ce62
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr108139.c
@@ -0,0 +1,18 @@
+/* { dg-do compile { target int128 } } */
+/* { dg-options "-O1 -ftree-vrp -fdump-tree-vrp" } */
+
+int a, b;
+int main() {
+  int c;
+  if (a > 1)
+    a++;
+  while (a)
+    if (c == b)
+      c = a;
+  return 0;
+}
+
+
+/* { dg-final { scan-tree-dump-not "Folding predicate" "vrp2" } } */
+
+