Check the VN of the src register at the two copies, not just the

register number.

llvm-svn: 134309

1 files changed, 6 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/RegisterCoalescer.cpp b/llvm/lib/CodeGen/RegisterCoalescer.cpp
index d5025b9e636..13ae04283a9 100644
--- a/llvm/lib/CodeGen/RegisterCoalescer.cpp
+++ b/llvm/lib/CodeGen/RegisterCoalescer.cpp
@@ -1203,7 +1203,6 @@ static bool RegistersDefinedFromSameValue(LiveIntervals &li,
                                           VNInfo *VNI,
                                           LiveRange *LR,
                                      SmallVector<MachineInstr*, 8> &DupCopies) {
-  return false; // To see if this fixes the i386 dragonegg buildbot miscompile.
   // FIXME: This is very conservative. For example, we don't handle
   // physical registers.
 
@@ -1252,6 +1251,12 @@ static bool RegistersDefinedFromSameValue(LiveIntervals &li,
   if (Src != OtherSrc)
     return false;
 
+  // If the copies use two different value numbers of X, we cannot merge
+  // A and B.
+  if (SrcInt.FindLiveRangeContaining(Other->def)->valno !=
+      SrcInt.FindLiveRangeContaining(VNI->def)->valno)
+    return false;
+
   DupCopies.push_back(MI);
 
   return true;