Simplify demanded bits of select sources where the condition is a constant vector

llvm-svn: 160835

2 files changed, 34 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index eb9945b6817..bdd97a862b7 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -899,5 +899,16 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
     return &SI;
   }
 
+  if (VectorType* VecTy = dyn_cast<VectorType>(SI.getType())) {
+    unsigned VWidth = VecTy->getNumElements();
+    APInt UndefElts(VWidth, 0);
+    APInt AllOnesEltMask(APInt::getAllOnesValue(VWidth));
+    if (Value *V = SimplifyDemandedVectorElts(&SI, AllOnesEltMask, UndefElts)) {
+      if (V != &SI)
+        return ReplaceInstUsesWith(SI, V);
+      return &SI;
+    }
+  }
+
   return 0;
 }
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index 46ba83b6513..54be8ed3fa9 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -989,6 +989,29 @@ Value *InstCombiner::SimplifyDemandedVectorElts(Value *V, APInt DemandedElts,
     }
     break;
   }
+  case Instruction::Select: {
+    APInt LeftDemanded(DemandedElts), RightDemanded(DemandedElts);
+    if (ConstantVector* CV = dyn_cast<ConstantVector>(I->getOperand(0))) {
+      for (unsigned i = 0; i < VWidth; i++) {
+        if (CV->getAggregateElement(i)->isNullValue())
+          LeftDemanded.clearBit(i);
+        else
+          RightDemanded.clearBit(i);
+      }
+    }
+
+    TmpV = SimplifyDemandedVectorElts(I->getOperand(1), LeftDemanded,
+                                      UndefElts, Depth+1);
+    if (TmpV) { I->setOperand(1, TmpV); MadeChange = true; }
+
+    TmpV = SimplifyDemandedVectorElts(I->getOperand(2), RightDemanded,
+                                      UndefElts2, Depth+1);
+    if (TmpV) { I->setOperand(2, TmpV); MadeChange = true; }
+      
+    // Output elements are undefined if both are undefined.
+    UndefElts &= UndefElts2;
+    break;
+  }
   case Instruction::BitCast: {
     // Vector->vector casts only.
     VectorType *VTy = dyn_cast<VectorType>(I->getOperand(0)->getType());