[ScalarizeMaskedMemIntrin] Use poison instead of undef as placeholder [NFC]

This is used for masked out lanes, that are replaced with the passthrough value

Author: nunoplopes

llvm/lib/Transforms/Scalar/ScalarizeMaskedMemIntrin.cpp

@@ -125,7 +125,7 @@ static unsigned adjustForEndian(const DataLayout &DL, unsigned VectorWidth,
 //  br label %else
 //
 // else:                                             ; preds = %0, %cond.load
-//  %res.phi.else = phi <16 x i32> [ %5, %cond.load ], [ undef, %0 ]
+//  %res.phi.else = phi <16 x i32> [ %5, %cond.load ], [ poison, %0 ]
 //  %6 = extractelement <16 x i1> %mask, i32 1
 //  br i1 %6, label %cond.load1, label %else2
 //
@@ -386,11 +386,11 @@ static void scalarizeMaskedStore(const DataLayout &DL, CallInst *CI,
 // cond.load:
 // %Ptr0 = extractelement <16 x i32*> %Ptrs, i32 0
 // %Load0 = load i32, i32* %Ptr0, align 4
-// %Res0 = insertelement <16 x i32> undef, i32 %Load0, i32 0
+// %Res0 = insertelement <16 x i32> poison, i32 %Load0, i32 0
 // br label %else
 //
 // else:
-// %res.phi.else = phi <16 x i32>[%Res0, %cond.load], [undef, %0]
+// %res.phi.else = phi <16 x i32>[%Res0, %cond.load], [poison, %0]
 // %Mask1 = extractelement <16 x i1> %Mask, i32 1
 // br i1 %Mask1, label %cond.load1, label %else2
 //
@@ -645,7 +645,7 @@ static void scalarizeMaskedExpandLoad(const DataLayout &DL, CallInst *CI,
   Value *VResult = PassThru;
 
   // Shorten the way if the mask is a vector of constants.
-  // Create a build_vector pattern, with loads/undefs as necessary and then
+  // Create a build_vector pattern, with loads/poisons as necessary and then
   // shuffle blend with the pass through value.
   if (isConstantIntVector(Mask)) {
     unsigned MemIndex = 0;
@@ -654,7 +654,7 @@ static void scalarizeMaskedExpandLoad(const DataLayout &DL, CallInst *CI,
     for (unsigned Idx = 0; Idx < VectorWidth; ++Idx) {
       Value *InsertElt;
       if (cast<Constant>(Mask)->getAggregateElement(Idx)->isNullValue()) {
-        InsertElt = UndefValue::get(EltTy);
+        InsertElt = PoisonValue::get(EltTy);
         ShuffleMask[Idx] = Idx + VectorWidth;
       } else {
         Value *NewPtr =

llvm/test/Transforms/ScalarizeMaskedMemIntrin/X86/expand-masked-expandload.ll

@@ -47,7 +47,7 @@ define <2 x i64> @scalarize_v2i64_ones_mask(ptr %p, <2 x i64> %passthru) {
 
 define <2 x i64> @scalarize_v2i64_zero_mask(ptr %p, <2 x i64> %passthru) {
 ; CHECK-LABEL: @scalarize_v2i64_zero_mask(
-; CHECK-NEXT:    [[TMP1:%.*]] = shufflevector <2 x i64> undef, <2 x i64> [[PASSTHRU:%.*]], <2 x i32> <i32 2, i32 3>
+; CHECK-NEXT:    [[TMP1:%.*]] = shufflevector <2 x i64> poison, <2 x i64> [[PASSTHRU:%.*]], <2 x i32> <i32 2, i32 3>
 ; CHECK-NEXT:    ret <2 x i64> [[TMP1]]
 ;
   %ret = call <2 x i64> @llvm.masked.expandload.v2i64.p0(ptr %p, <2 x i1> <i1 false, i1 false>, <2 x i64> %passthru)
@@ -58,7 +58,7 @@ define <2 x i64> @scalarize_v2i64_const_mask(ptr %p, <2 x i64> %passthru) {
 ; CHECK-LABEL: @scalarize_v2i64_const_mask(
 ; CHECK-NEXT:    [[TMP1:%.*]] = getelementptr inbounds i64, ptr [[P:%.*]], i32 0
 ; CHECK-NEXT:    [[LOAD1:%.*]] = load i64, ptr [[TMP1]], align 1
-; CHECK-NEXT:    [[RES1:%.*]] = insertelement <2 x i64> <i64 undef, i64 poison>, i64 [[LOAD1]], i64 1
+; CHECK-NEXT:    [[RES1:%.*]] = insertelement <2 x i64> poison, i64 [[LOAD1]], i64 1
 ; CHECK-NEXT:    [[TMP2:%.*]] = shufflevector <2 x i64> [[RES1]], <2 x i64> [[PASSTHRU:%.*]], <2 x i32> <i32 2, i32 1>
 ; CHECK-NEXT:    ret <2 x i64> [[TMP2]]
 ;