[DAGCombiner] isAllOnesConstantOrAllOnesSplatConstant(): look through bitcasts

Summary:
As pointed out in D46528, we errneously transform cases like `xor X, -1`,
even though we use said function.
It's because the `-1` is actually a bitcast there.
So i think we can just look through it in the function.

Differential Revision: https://reviews.llvm.org/D47156

llvm-svn: 332905

1 files changed, 9 insertions, 6 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index fc16a06bd99..93d9cfd73bd 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -860,6 +860,12 @@ bool DAGCombiner::isOneUseSetCC(SDValue N) const {
   return false;
 }
 
+static SDValue peekThroughBitcast(SDValue V) {
+  while (V.getOpcode() == ISD::BITCAST)
+    V = V.getOperand(0);
+  return V;
+}
+
 // Returns the SDNode if it is a constant float BuildVector
 // or constant float.
 static SDNode *isConstantFPBuildVectorOrConstantFP(SDValue N) {
@@ -894,6 +900,7 @@ static bool isConstantOrConstantVector(SDValue N, bool NoOpaques = false) {
 // constant null integer (with no undefs).
 // Build vector implicit truncation is not an issue for null values.
 static bool isNullConstantOrNullSplatConstant(SDValue N) {
+  // TODO: may want to use peekThroughBitcast() here.
   if (ConstantSDNode *Splat = isConstOrConstSplat(N))
     return Splat->isNullValue();
   return false;
@@ -903,6 +910,7 @@ static bool isNullConstantOrNullSplatConstant(SDValue N) {
 // constant integer of one (with no undefs).
 // Do not permit build vector implicit truncation.
 static bool isOneConstantOrOneSplatConstant(SDValue N) {
+  // TODO: may want to use peekThroughBitcast() here.
   unsigned BitWidth = N.getScalarValueSizeInBits();
   if (ConstantSDNode *Splat = isConstOrConstSplat(N))
     return Splat->isOne() && Splat->getAPIntValue().getBitWidth() == BitWidth;
@@ -913,6 +921,7 @@ static bool isOneConstantOrOneSplatConstant(SDValue N) {
 // constant integer of all ones (with no undefs).
 // Do not permit build vector implicit truncation.
 static bool isAllOnesConstantOrAllOnesSplatConstant(SDValue N) {
+  N = peekThroughBitcast(N);
   unsigned BitWidth = N.getScalarValueSizeInBits();
   if (ConstantSDNode *Splat = isConstOrConstSplat(N))
     return Splat->isAllOnesValue() &&
@@ -13055,12 +13064,6 @@ bool DAGCombiner::isMulAddWithConstProfitable(SDNode *MulNode,
   return false;
 }
 
-static SDValue peekThroughBitcast(SDValue V) {
-  while (V.getOpcode() == ISD::BITCAST)
-    V = V.getOperand(0);
-  return V;
-}
-
 SDValue DAGCombiner::getMergeStoreChains(SmallVectorImpl<MemOpLink> &StoreNodes,
                                          unsigned NumStores) {
   SmallVector<SDValue, 8> Chains;