Fix a logic error. An instruction that has a live physical register def cannot be CSE'ed, but it *can* be used to replace a common subexpression.

llvm-svn: 97688

1 files changed, 5 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/MachineCSE.cpp b/llvm/lib/CodeGen/MachineCSE.cpp
index ea11bfbdb89..d542cc9969a 100644
--- a/llvm/lib/CodeGen/MachineCSE.cpp
+++ b/llvm/lib/CodeGen/MachineCSE.cpp
@@ -128,8 +128,6 @@ bool MachineCSE::ProcessBlock(MachineDomTreeNode *Node) {
     if (TII->isMoveInstr(*MI, SrcReg, DstReg, SrcSubIdx, DstSubIdx) ||
         MI->isExtractSubreg() || MI->isInsertSubreg() || MI->isSubregToReg())
       continue;    
-    if (hasLivePhysRegDefUse(MI))
-      continue;
 
     bool FoundCSE = VNT.count(MI);
     if (!FoundCSE) {
@@ -138,6 +136,11 @@ bool MachineCSE::ProcessBlock(MachineDomTreeNode *Node) {
         FoundCSE = VNT.count(MI);
     }
 
+    // If the instruction defines a physical register and the value *may* be
+    // used, then it's not safe to replace it with a common subexpression.
+    if (FoundCSE && hasLivePhysRegDefUse(MI))
+      FoundCSE = false;
+
     if (!FoundCSE) {
       VNT.insert(MI, CurrVN++);
       Exps.push_back(MI);