[EarlyCSE] Take the intersection of flags on instructions

EarlyCSE had inconsistent behavior with regards to flag'd instructions:
- In some cases, it would pessimize if the available instruction had
  different flags by not performing CSE.
- In other cases, it would miscompile if it replaced an instruction
  which had no flags with an instruction which has flags.

Fix this by being more consistent with our flag handling by utilizing
andIRFlags.

llvm-svn: 267111

1 files changed, 3 insertions, 10 deletions

diff --git a/llvm/lib/Transforms/Scalar/EarlyCSE.cpp b/llvm/lib/Transforms/Scalar/EarlyCSE.cpp
index 7be3aab272d..1d7da48321d 100644
--- a/llvm/lib/Transforms/Scalar/EarlyCSE.cpp
+++ b/llvm/lib/Transforms/Scalar/EarlyCSE.cpp
@@ -153,7 +153,7 @@ bool DenseMapInfo<SimpleValue>::isEqual(SimpleValue LHS, SimpleValue RHS) {
 
   if (LHSI->getOpcode() != RHSI->getOpcode())
     return false;
-  if (LHSI->isIdenticalTo(RHSI))
+  if (LHSI->isIdenticalToWhenDefined(RHSI))
     return true;
 
   // If we're not strictly identical, we still might be a commutable instruction
@@ -165,15 +165,6 @@ bool DenseMapInfo<SimpleValue>::isEqual(SimpleValue LHS, SimpleValue RHS) {
            "same opcode, but different instruction type?");
     BinaryOperator *RHSBinOp = cast<BinaryOperator>(RHSI);
 
-    // Check overflow attributes
-    if (isa<OverflowingBinaryOperator>(LHSBinOp)) {
-      assert(isa<OverflowingBinaryOperator>(RHSBinOp) &&
-             "same opcode, but different operator type?");
-      if (LHSBinOp->hasNoUnsignedWrap() != RHSBinOp->hasNoUnsignedWrap() ||
-          LHSBinOp->hasNoSignedWrap() != RHSBinOp->hasNoSignedWrap())
-        return false;
-    }
-
     // Commuted equality
     return LHSBinOp->getOperand(0) == RHSBinOp->getOperand(1) &&
            LHSBinOp->getOperand(1) == RHSBinOp->getOperand(0);
@@ -584,6 +575,8 @@ bool EarlyCSE::processNode(DomTreeNode *Node) {
       // See if the instruction has an available value.  If so, use it.
       if (Value *V = AvailableValues.lookup(Inst)) {
         DEBUG(dbgs() << "EarlyCSE CSE: " << *Inst << "  to: " << *V << '\n');
+        if (auto *I = dyn_cast<Instruction>(V))
+          I->andIRFlags(Inst);
         Inst->replaceAllUsesWith(V);
         Inst->eraseFromParent();
         Changed = true;