[InstCombine] Masked loads with undef masks can fold to normal loads

We were able to fold masked loads with an all-ones mask to a normal
load.  However, we couldn't turn a masked load with a mask with mixed
ones and undefs into a normal load.

llvm-svn: 275380

1 files changed, 19 insertions, 6 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index 36c9762eff4..8acff91345d 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -1038,14 +1038,27 @@ static Value *simplifyMinnumMaxnum(const IntrinsicInst &II) {
   return nullptr;
 }
 
-static Value *simplifyMaskedLoad(const IntrinsicInst &II,
-                                 InstCombiner::BuilderTy &Builder) {
-  auto *ConstMask = dyn_cast<Constant>(II.getArgOperand(2));
+static bool maskIsAllOneOrUndef(Value *Mask) {
+  auto *ConstMask = dyn_cast<Constant>(Mask);
   if (!ConstMask)
-    return nullptr;
+    return false;
+  if (ConstMask->isAllOnesValue() || isa<UndefValue>(ConstMask))
+    return true;
+  for (unsigned I = 0, E = ConstMask->getType()->getVectorNumElements(); I != E;
+       ++I) {
+    if (auto *MaskElt = ConstMask->getAggregateElement(I))
+      if (MaskElt->isAllOnesValue() || isa<UndefValue>(MaskElt))
+        continue;
+    return false;
+  }
+  return true;
+}
 
-  // If the mask is all ones, this is a plain vector load of the 1st argument.
-  if (ConstMask->isAllOnesValue()) {
+static Value *simplifyMaskedLoad(const IntrinsicInst &II,
+                                 InstCombiner::BuilderTy &Builder) {
+  // If the mask is all ones or undefs, this is a plain vector load of the 1st
+  // argument.
+  if (maskIsAllOneOrUndef(II.getArgOperand(2))) {
     Value *LoadPtr = II.getArgOperand(0);
     unsigned Alignment = cast<ConstantInt>(II.getArgOperand(1))->getZExtValue();
     return Builder.CreateAlignedLoad(LoadPtr, Alignment, "unmaskedload");