From: Richard Biener <rguenther@suse.de>
Date: Thu, 10 Nov 2022 14:02:37 +0000 (+0100)
Subject: better PHI copy propagation for forwprop
X-Git-Tag: basepoints/gcc-14~3328
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f1b76811f2c3773e8cabcc07932bf13e82e264db;p=thirdparty%2Fgcc.git

better PHI copy propagation for forwprop

We can handle _1 = PHI <_1, _2> as a copy.

	PR tree-optimization/84646
	* tree-ssa-forwprop.cc (pass_forwprop::execute): Improve
	copy propagation across PHIs.
---

diff --git a/gcc/tree-ssa-forwprop.cc b/gcc/tree-ssa-forwprop.cc
index 4b693ef095c5..7c7942600ef2 100644
--- a/gcc/tree-ssa-forwprop.cc
+++ b/gcc/tree-ssa-forwprop.cc
@@ -3384,7 +3384,12 @@ pass_forwprop::execute (function *fun)
 	  FOR_EACH_PHI_ARG (use_p, phi, it, SSA_OP_USE)
 	    {
 	      tree use = USE_FROM_PTR (use_p);
-	      if (! first)
+	      if (use == res)
+		/* The PHI result can also appear on a backedge, if so
+		   we can ignore this case for the purpose of determining
+		   the singular value.  */
+		;
+	      else if (! first)
 		first = use;
 	      else if (! operand_equal_p (first, use, 0))
 		{