+/// FoldBitCast - Constant fold bitcast, symbolically evaluating it with
+/// TargetData. This always returns a non-null constant, but it may be a
+/// ConstantExpr if unfoldable.
+static Constant *FoldBitCast(Constant *C, const Type *DestTy,
+ const TargetData &TD) {
+
+ // This only handles casts to vectors currently.
+ const VectorType *DestVTy = dyn_cast<VectorType>(DestTy);
+ if (DestVTy == 0)
+ return ConstantExpr::getBitCast(C, DestTy);
+
+ // If this is a scalar -> vector cast, convert the input into a <1 x scalar>
+ // vector so the code below can handle it uniformly.
+ if (isa<ConstantFP>(C) || isa<ConstantInt>(C)) {
+ Constant *Ops = C; // don't take the address of C!
+ return FoldBitCast(ConstantVector::get(&Ops, 1), DestTy, TD);
+ }
+
+ // If this is a bitcast from constant vector -> vector, fold it.
+ ConstantVector *CV = dyn_cast<ConstantVector>(C);
+ if (CV == 0)
+ return ConstantExpr::getBitCast(C, DestTy);
+
+ // If the element types match, VMCore can fold it.
+ unsigned NumDstElt = DestVTy->getNumElements();
+ unsigned NumSrcElt = CV->getNumOperands();
+ if (NumDstElt == NumSrcElt)
+ return ConstantExpr::getBitCast(C, DestTy);
+
+ const Type *SrcEltTy = CV->getType()->getElementType();
+ const Type *DstEltTy = DestVTy->getElementType();
+
+ // Otherwise, we're changing the number of elements in a vector, which
+ // requires endianness information to do the right thing. For example,
+ // bitcast (<2 x i64> <i64 0, i64 1> to <4 x i32>)
+ // folds to (little endian):
+ // <4 x i32> <i32 0, i32 0, i32 1, i32 0>
+ // and to (big endian):
+ // <4 x i32> <i32 0, i32 0, i32 0, i32 1>
+
+ // First thing is first. We only want to think about integer here, so if
+ // we have something in FP form, recast it as integer.
+ if (DstEltTy->isFloatingPointTy()) {
+ // Fold to an vector of integers with same size as our FP type.
+ unsigned FPWidth = DstEltTy->getPrimitiveSizeInBits();
+ const Type *DestIVTy =
+ VectorType::get(IntegerType::get(C->getContext(), FPWidth), NumDstElt);
+ // Recursively handle this integer conversion, if possible.
+ C = FoldBitCast(C, DestIVTy, TD);
+ if (!C) return ConstantExpr::getBitCast(C, DestTy);
+
+ // Finally, VMCore can handle this now that #elts line up.
+ return ConstantExpr::getBitCast(C, DestTy);
+ }
+
+ // Okay, we know the destination is integer, if the input is FP, convert
+ // it to integer first.
+ if (SrcEltTy->isFloatingPointTy()) {
+ unsigned FPWidth = SrcEltTy->getPrimitiveSizeInBits();
+ const Type *SrcIVTy =
+ VectorType::get(IntegerType::get(C->getContext(), FPWidth), NumSrcElt);
+ // Ask VMCore to do the conversion now that #elts line up.
+ C = ConstantExpr::getBitCast(C, SrcIVTy);
+ CV = dyn_cast<ConstantVector>(C);
+ if (!CV) // If VMCore wasn't able to fold it, bail out.
+ return C;
+ }
+
+ // Now we know that the input and output vectors are both integer vectors
+ // of the same size, and that their #elements is not the same. Do the
+ // conversion here, which depends on whether the input or output has
+ // more elements.
+ bool isLittleEndian = TD.isLittleEndian();
+
+ SmallVector<Constant*, 32> Result;
+ if (NumDstElt < NumSrcElt) {
+ // Handle: bitcast (<4 x i32> <i32 0, i32 1, i32 2, i32 3> to <2 x i64>)
+ Constant *Zero = Constant::getNullValue(DstEltTy);
+ unsigned Ratio = NumSrcElt/NumDstElt;
+ unsigned SrcBitSize = SrcEltTy->getPrimitiveSizeInBits();
+ unsigned SrcElt = 0;
+ for (unsigned i = 0; i != NumDstElt; ++i) {
+ // Build each element of the result.
+ Constant *Elt = Zero;
+ unsigned ShiftAmt = isLittleEndian ? 0 : SrcBitSize*(Ratio-1);
+ for (unsigned j = 0; j != Ratio; ++j) {
+ Constant *Src = dyn_cast<ConstantInt>(CV->getOperand(SrcElt++));
+ if (!Src) // Reject constantexpr elements.
+ return ConstantExpr::getBitCast(C, DestTy);
+
+ // Zero extend the element to the right size.
+ Src = ConstantExpr::getZExt(Src, Elt->getType());
+
+ // Shift it to the right place, depending on endianness.
+ Src = ConstantExpr::getShl(Src,
+ ConstantInt::get(Src->getType(), ShiftAmt));
+ ShiftAmt += isLittleEndian ? SrcBitSize : -SrcBitSize;
+
+ // Mix it in.
+ Elt = ConstantExpr::getOr(Elt, Src);
+ }
+ Result.push_back(Elt);
+ }
+ } else {
+ // Handle: bitcast (<2 x i64> <i64 0, i64 1> to <4 x i32>)
+ unsigned Ratio = NumDstElt/NumSrcElt;
+ unsigned DstBitSize = DstEltTy->getPrimitiveSizeInBits();
+
+ // Loop over each source value, expanding into multiple results.
+ for (unsigned i = 0; i != NumSrcElt; ++i) {
+ Constant *Src = dyn_cast<ConstantInt>(CV->getOperand(i));
+ if (!Src) // Reject constantexpr elements.
+ return ConstantExpr::getBitCast(C, DestTy);
+
+ unsigned ShiftAmt = isLittleEndian ? 0 : DstBitSize*(Ratio-1);
+ for (unsigned j = 0; j != Ratio; ++j) {
+ // Shift the piece of the value into the right place, depending on
+ // endianness.
+ Constant *Elt = ConstantExpr::getLShr(Src,
+ ConstantInt::get(Src->getType(), ShiftAmt));
+ ShiftAmt += isLittleEndian ? DstBitSize : -DstBitSize;
+
+ // Truncate and remember this piece.
+ Result.push_back(ConstantExpr::getTrunc(Elt, DstEltTy));
+ }
+ }
+ }
+
+ return ConstantVector::get(Result.data(), Result.size());
+}
+
+