From: Ben.Lippmeier@anu.edu.au <unknown>
Date: Sat, 18 Apr 2009 08:22:53 +0000 (+0000)
Subject: Fix #3170: Allow coalescing of the same node during register allocation.
X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=commitdiff_plain;h=2d4952d959b3056cff6de9d1663c621d2b4efc70

Fix #3170: Allow coalescing of the same node during register allocation.
  The x86 code generator sometimes generates nop moves like
  movl %vI_a %vI_a, but we'll just ignore them for coalescing
  purposes instead of emitting an error. It shouldn't hurt anything.
---

diff --git a/compiler/utils/GraphOps.hs b/compiler/utils/GraphOps.hs
index 8183e0b..17c14d0 100644
--- a/compiler/utils/GraphOps.hs
+++ b/compiler/utils/GraphOps.hs
@@ -335,6 +335,9 @@ coalesceNodes aggressive triv graph (k1, k2)
 	, not $ elementOfUniqSet kMin (nodeConflicts nMax)
 	, not $ elementOfUniqSet kMax (nodeConflicts nMin)
 
+	-- can't coalesce the same node
+	, nodeId nMin /= nodeId nMax
+
 	= coalesceNodes_merge aggressive triv graph kMin kMax nMin nMax
 
 	-- don't do the coalescing after all
@@ -350,9 +353,6 @@ coalesceNodes_merge aggressive triv graph kMin kMax nMin nMax
 	| not (isNothing (nodeColor nMin) && isNothing (nodeColor nMax))
 	= error "GraphOps.coalesceNodes: can't coalesce colored nodes."
 
-	| nodeId nMin == nodeId nMax
-	= error "GraphOps.coalesceNodes: can't coalesce the same node."
-
 	---
 	| otherwise
 	= let