[InstCombine] generalize safe vector constant utility

This is almost NFC, but there could be some case where the original
code had undefs in the constants (rather than just the shuffle mask),
and we'll use safe constants rather than undefs now.

The FIXME noted in foldShuffledBinop() is already visible in existing
tests, so correcting that is the next step.

llvm-svn: 336558

1 files changed, 16 insertions, 9 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
index 75fec3e79d3..452079354e4 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
+++ b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
@@ -212,19 +212,26 @@ IntrinsicIDToOverflowCheckFlavor(unsigned ID) {
   }
 }
 
-/// Integer division/remainder require special handling to avoid undefined
+/// Some binary operators require special handling to avoid poison and undefined
 /// behavior. If a constant vector has undef elements, replace those undefs with
-/// '1' because that's always safe to execute.
-static inline Constant *getSafeVectorConstantForIntDivRem(Constant *In) {
-  assert(In->getType()->isVectorTy() && "Not expecting scalars here");
-  assert(In->getType()->getVectorElementType()->isIntegerTy() &&
-         "Not expecting FP opcodes/operands/constants here");
-
-  unsigned NumElts = In->getType()->getVectorNumElements();
+/// identity constants because those are always safe to execute. If no identity
+/// constant exists, replace undef with '1' or '1.0'.
+static inline Constant *getSafeVectorConstantForBinop(
+      BinaryOperator::BinaryOps Opcode, Constant *In) {
+  Type *Ty = In->getType();
+  assert(Ty->isVectorTy() && "Not expecting scalars here");
+
+  Type *EltTy = Ty->getVectorElementType();
+  Constant *IdentityC = ConstantExpr::getBinOpIdentity(Opcode, EltTy, true);
+  if (!IdentityC)
+    IdentityC = EltTy->isIntegerTy() ? ConstantInt::get(EltTy, 1):
+                                       ConstantFP::get(EltTy, 1.0);
+
+  unsigned NumElts = Ty->getVectorNumElements();
   SmallVector<Constant *, 16> Out(NumElts);
   for (unsigned i = 0; i != NumElts; ++i) {
     Constant *C = In->getAggregateElement(i);
-    Out[i] = isa<UndefValue>(C) ? ConstantInt::get(C->getType(), 1) : C;
+    Out[i] = isa<UndefValue>(C) ? IdentityC : C;
   }
   return ConstantVector::get(Out);
 }