From: Andrew MacLeod <amacleod@redhat.com>
Date: Fri, 16 Dec 2022 21:53:31 +0000 (-0500)
Subject: Don't use PHI equivalences in range-on-entry.
X-Git-Tag: basepoints/gcc-14~2401
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=0bdd2261c254f08b0f4437c156b79711d68c6e7f;p=thirdparty%2Fgcc.git

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 ce5a0c8155e6..9848d140242f 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 000000000000..6f224e3ce629
--- /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" } } */
+
+