From: Jakob Stoklund Olesen <stoklund@2pi.dk>
Date: Thu, 15 Sep 2011 04:52:06 +0000 (+0000)
Subject: It is safe to remat a value killed by phis.
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=4ea24e993f179113a9bb76ee152cc490e738c936;p=oota-llvm.git

It is safe to remat a value killed by phis.

The source live range is recomputed using shrinkToUses() which does
handle phis correctly.  The hasPHIKill() condition was relevant in the
old days when ReMaterializeTrivialDef() tried to recompute the live
range itself.

The shrinkToUses() function will mark the original def as dead when no
more uses and phi kills remain.  It is then removed by
runOnMachineFunction().

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@139781 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/CodeGen/RegisterCoalescer.cpp b/lib/CodeGen/RegisterCoalescer.cpp
index f3b8ae33c6a..674d075c4f8 100644
--- a/lib/CodeGen/RegisterCoalescer.cpp
+++ b/lib/CodeGen/RegisterCoalescer.cpp
@@ -805,9 +805,7 @@ bool RegisterCoalescer::ReMaterializeTrivialDef(LiveInterval &SrcInt,
   LiveInterval::iterator SrcLR = SrcInt.FindLiveRangeContaining(CopyIdx);
   assert(SrcLR != SrcInt.end() && "Live range not found!");
   VNInfo *ValNo = SrcLR->valno;
-  // If other defs can reach uses of this def, then it's not safe to perform
-  // the optimization.
-  if (ValNo->isPHIDef() || ValNo->isUnused() || ValNo->hasPHIKill())
+  if (ValNo->isPHIDef() || ValNo->isUnused())
     return false;
   MachineInstr *DefMI = LIS->getInstructionFromIndex(ValNo->def);
   if (!DefMI)