[ScalarizeMaskedMemIntrin] When expanding masked loads, start with the passthru value and insert each conditional load result over their element.

Previously we started with undef and did one final merge at the end with a select.

llvm-svn: 343271

1 files changed, 12 insertions, 22 deletions

diff --git a/llvm/lib/CodeGen/ScalarizeMaskedMemIntrin.cpp b/llvm/lib/CodeGen/ScalarizeMaskedMemIntrin.cpp
index 35580df42f1..b039cdd01d4 100644
--- a/llvm/lib/CodeGen/ScalarizeMaskedMemIntrin.cpp
+++ b/llvm/lib/CodeGen/ScalarizeMaskedMemIntrin.cpp
@@ -90,7 +90,7 @@ FunctionPass *llvm::createScalarizeMaskedMemIntrinPass() {
 // cond.load:                                        ; preds = %0
 //  %3 = getelementptr i32* %1, i32 0
 //  %4 = load i32* %3
-//  %5 = insertelement <16 x i32> undef, i32 %4, i32 0
+//  %5 = insertelement <16 x i32> %passthru, i32 %4, i32 0
 //  br label %else
 //
 // else:                                             ; preds = %0, %cond.load
@@ -146,10 +146,8 @@ static void scalarizeMaskedLoad(CallInst *CI) {
   Value *FirstEltPtr = Builder.CreateBitCast(Ptr, NewPtrType);
   unsigned VectorWidth = VecType->getNumElements();
 
-  Value *UndefVal = UndefValue::get(VecType);
-
   // The result vector
-  Value *VResult = UndefVal;
+  Value *VResult = Src0;
 
   if (isa<Constant>(Mask)) {
     for (unsigned Idx = 0; Idx < VectorWidth; ++Idx) {
@@ -161,15 +159,11 @@ static void scalarizeMaskedLoad(CallInst *CI) {
       VResult =
           Builder.CreateInsertElement(VResult, Load, Builder.getInt32(Idx));
     }
-    Value *NewI = Builder.CreateSelect(Mask, VResult, Src0);
-    CI->replaceAllUsesWith(NewI);
+    CI->replaceAllUsesWith(VResult);
     CI->eraseFromParent();
     return;
   }
 
-  PHINode *Phi = nullptr;
-  Value *PrevPhi = UndefVal;
-
   for (unsigned Idx = 0; Idx < VectorWidth; ++Idx) {
     // Fill the "else" block, created in the previous iteration
     //
@@ -177,13 +171,6 @@ static void scalarizeMaskedLoad(CallInst *CI) {
     //  %mask_1 = extractelement <16 x i1> %mask, i32 Idx
     //  br i1 %mask_1, label %cond.load, label %else
     //
-    if (Idx > 0) {
-      Phi = Builder.CreatePHI(VecType, 2, "res.phi.else");
-      Phi->addIncoming(VResult, CondBlock);
-      Phi->addIncoming(PrevPhi, PrevIfBlock);
-      PrevPhi = Phi;
-      VResult = Phi;
-    }
 
     Value *Predicate =
         Builder.CreateExtractElement(Mask, Builder.getInt32(Idx));
@@ -200,7 +187,8 @@ static void scalarizeMaskedLoad(CallInst *CI) {
     Value *Gep =
         Builder.CreateInBoundsGEP(EltTy, FirstEltPtr, Builder.getInt32(Idx));
     LoadInst *Load = Builder.CreateAlignedLoad(Gep, AlignVal);
-    VResult = Builder.CreateInsertElement(VResult, Load, Builder.getInt32(Idx));
+    Value *NewVResult = Builder.CreateInsertElement(VResult, Load,
+                                                    Builder.getInt32(Idx));
 
     // Create "else" block, fill it in the next iteration
     BasicBlock *NewIfBlock =
@@ -211,13 +199,15 @@ static void scalarizeMaskedLoad(CallInst *CI) {
     OldBr->eraseFromParent();
     PrevIfBlock = IfBlock;
     IfBlock = NewIfBlock;
+
+    // Create the phi to join the new and previous value.
+    PHINode *Phi = Builder.CreatePHI(VecType, 2, "res.phi.else");
+    Phi->addIncoming(NewVResult, CondBlock);
+    Phi->addIncoming(VResult, PrevIfBlock);
+    VResult = Phi;
   }
 
-  Phi = Builder.CreatePHI(VecType, 2, "res.phi.select");
-  Phi->addIncoming(VResult, CondBlock);
-  Phi->addIncoming(PrevPhi, PrevIfBlock);
-  Value *NewI = Builder.CreateSelect(Mask, Phi, Src0);
-  CI->replaceAllUsesWith(NewI);
+  CI->replaceAllUsesWith(VResult);
   CI->eraseFromParent();
 }