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From: Eric Botcazou <>
Subject: [PATCH] Reduce DF computation at -O0
Date: Thu, 06 Oct 2022 19:25:53 +0200	[thread overview]
Message-ID: <2601473.BddDVKsqQX@fomalhaut> (raw)

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even at -O0 there may be a fair amount of DF computation performed when
compiling large units and part of it appears to be useless.

Bootstrapped/regtested on x86-64/Linux, OK for the mainline?

2022-10-06  Eric Botcazou  <>

	* (thread_prologue_and_epilogue_insns): Update only entry
	and exit blocks when not optimizing.  Remove dead statement.

Eric Botcazou

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diff --git a/gcc/ b/gcc/
index 5498a712c4a..6474a663b30 100644
--- a/gcc/
+++ b/gcc/
@@ -6249,10 +6249,15 @@ thread_prologue_and_epilogue_insns (void)
-  /* Threading the prologue and epilogue changes the artificial refs
-     in the entry and exit blocks.  */
-  epilogue_completed = 1;
-  df_update_entry_exit_and_calls ();
+  /* Threading the prologue and epilogue changes the artificial refs in the
+     entry and exit blocks, and may invalidate DF info for tail calls.  */
+  if (optimize)
+    df_update_entry_exit_and_calls ();
+  else
+    {
+      df_update_entry_block_defs ();
+      df_update_exit_block_uses ();
+    }
 /* Reposition the prologue-end and epilogue-begin notes after

             reply	other threads:[~2022-10-06 17:26 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-10-06 17:25 Eric Botcazou [this message]
2022-10-07  6:07 ` Richard Biener

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