Bitcasts are transitive. Bitcast-Bitcast-X becomes Bitcast-X.

llvm-svn: 138722

2 files changed, 11 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/ConstantFolding.cpp b/llvm/lib/Analysis/ConstantFolding.cpp
index df79849c3cf..613804d6d2d 100644
--- a/llvm/lib/Analysis/ConstantFolding.cpp
+++ b/llvm/lib/Analysis/ConstantFolding.cpp
@@ -51,6 +51,12 @@ static Constant *FoldBitCast(Constant *C, Type *DestTy,
   if (C->isAllOnesValue() && !DestTy->isX86_MMXTy())
     return Constant::getAllOnesValue(DestTy);
 
+  // Bitcast of Bitcast can be done using a single cast.
+  ConstantExpr *CE = dyn_cast<ConstantExpr>(C);
+  if (CE && CE->getOpcode() == Instruction::BitCast) {
+    return ConstantExpr::getBitCast(CE->getOperand(0), DestTy);
+  }
+
   // The code below only handles casts to vectors currently.
   VectorType *DestVTy = dyn_cast<VectorType>(DestTy);
   if (DestVTy == 0)
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
index ba90bf6b5c5..6c42c0c6600 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -1659,6 +1659,11 @@ Instruction *InstCombiner::visitBitCast(BitCastInst &CI) {
   if (DestTy == Src->getType())
     return ReplaceInstUsesWith(CI, Src);
 
+  // Bitcasts are transitive.
+  if (BitCastInst* BSrc = dyn_cast<BitCastInst>(Src)) {
+    return CastInst::Create(Instruction::BitCast, BSrc->getOperand(0), DestTy);
+  }
+
   if (PointerType *DstPTy = dyn_cast<PointerType>(DestTy)) {
     PointerType *SrcPTy = cast<PointerType>(SrcTy);
     Type *DstElTy = DstPTy->getElementType();