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From: Richard Biener <>
Subject: [PATCH] better PHI copy propagation for forwprop
Date: Thu, 10 Nov 2022 15:19:36 +0100 (CET)	[thread overview]
Message-ID: <> (raw)

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

Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed.

	PR tree-optimization/84646
	* (pass_forwprop::execute): Improve
	copy propagation across PHIs.
 gcc/ | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/gcc/ b/gcc/
index 4b693ef095c..7c7942600ef 100644
--- a/gcc/
+++ b/gcc/
@@ -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))

                 reply	other threads:[~2022-11-10 14:19 UTC|newest]

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