From 661c02e54ea72fb55205df0a717951ff28bb739e Mon Sep 17 00:00:00 2001
From: Andrew MacLeod <amacleod@redhat.com>
Date: Tue, 23 Nov 2021 14:12:29 -0500
Subject: [PATCH] Check for equivalences between PHI argument and def.

If a PHI argument on an edge is equivalent with the DEF, then it doesn't
provide any new information, defer processing it unless they are all
equivalences.

	PR tree-optimization/103359
	gcc/
	* gimple-range-fold.cc (fold_using_range::range_of_phi): If arg is
	equivalent to def, don't initially include it's range.

	gcc/testsuite/
	* gcc.dg/pr103359.c: New.
---
 gcc/gimple-range-fold.cc        | 16 ++++++++++++++++
 gcc/testsuite/gcc.dg/pr103359.c | 21 +++++++++++++++++++++
 2 files changed, 37 insertions(+)
 create mode 100644 gcc/testsuite/gcc.dg/pr103359.c

diff --git a/gcc/gimple-range-fold.cc b/gcc/gimple-range-fold.cc
index ec9690b05e4..d66ada5bb7c 100644
--- a/gcc/gimple-range-fold.cc
+++ b/gcc/gimple-range-fold.cc
@@ -771,6 +771,7 @@ fold_using_range::range_of_phi (irange &r, gphi *phi, fur_source &src)
   tree phi_def = gimple_phi_result (phi);
   tree type = gimple_range_type (phi);
   int_range_max arg_range;
+  int_range_max equiv_range;
   unsigned x;
 
   if (!type)
@@ -794,6 +795,16 @@ fold_using_range::range_of_phi (irange &r, gphi *phi, fur_source &src)
       // Get the range of the argument on its edge.
       src.get_phi_operand (arg_range, arg, e);
 
+      // Likewise, if the incoming PHI argument is equivalent to this
+      // PHI definition, it provides no new info.  Accumulate these ranges
+      // in case all arguments are equivalences.
+      if (src.query ()->query_relation (e, arg, phi_def, false) == EQ_EXPR)
+	{
+	  single_arg = arg;
+	  equiv_range.union_(arg_range);
+	  continue;
+	}
+
       if (!arg_range.undefined_p ())
 	{
 	  // Register potential dependencies for stale value tracking.
@@ -816,6 +827,11 @@ fold_using_range::range_of_phi (irange &r, gphi *phi, fur_source &src)
 	break;
     }
 
+    // If all arguments were equivalences, use the equivalence ranges as no
+    // arguments were processed.
+    if (!seen_arg)
+      r = equiv_range;
+
     // If the PHI boils down to a single effective argument, look at it.
     if (single_arg)
       {
diff --git a/gcc/testsuite/gcc.dg/pr103359.c b/gcc/testsuite/gcc.dg/pr103359.c
new file mode 100644
index 00000000000..13406f90d7d
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr103359.c
@@ -0,0 +1,21 @@
+/* { dg-do compile } */
+/* { dg-options "-O3 -fdump-tree-evrp" } */
+
+void foo();
+static char a, c;
+static int d, e;
+static short b(short f, short g) { return f * g; }
+int main() {
+  short h = 4;
+  for (; d;)
+    if (h)
+      if(e) {
+        if (!b(a & 1 | h, 3))
+          c = 0;
+        h = 1;
+      }
+  if (c)
+    foo();
+}
+
+/* { dg-final { scan-tree-dump-not "c = 0" "evrp" } } */