+/// ExtractConstantBytes - V is an integer constant which only has a subset of
+/// its bytes used. The bytes used are indicated by ByteStart (which is the
+/// first byte used, counting from the least significant byte) and ByteSize,
+/// which is the number of bytes used.
+///
+/// This function analyzes the specified constant to see if the specified byte
+/// range can be returned as a simplified constant. If so, the constant is
+/// returned, otherwise null is returned.
+///
+static Constant *ExtractConstantBytes(Constant *C, unsigned ByteStart,
+ unsigned ByteSize) {
+ assert(C->getType()->isIntegerTy() &&
+ (cast<IntegerType>(C->getType())->getBitWidth() & 7) == 0 &&
+ "Non-byte sized integer input");
+ unsigned CSize = cast<IntegerType>(C->getType())->getBitWidth()/8;
+ assert(ByteSize && "Must be accessing some piece");
+ assert(ByteStart+ByteSize <= CSize && "Extracting invalid piece from input");
+ assert(ByteSize != CSize && "Should not extract everything");
+
+ // Constant Integers are simple.
+ if (ConstantInt *CI = dyn_cast<ConstantInt>(C)) {
+ APInt V = CI->getValue();
+ if (ByteStart)
+ V = V.lshr(ByteStart*8);
+ V.trunc(ByteSize*8);
+ return ConstantInt::get(CI->getContext(), V);
+ }
+
+ // In the input is a constant expr, we might be able to recursively simplify.
+ // If not, we definitely can't do anything.
+ ConstantExpr *CE = dyn_cast<ConstantExpr>(C);
+ if (CE == 0) return 0;
+
+ switch (CE->getOpcode()) {
+ default: return 0;
+ case Instruction::Or: {
+ Constant *RHS = ExtractConstantBytes(CE->getOperand(1), ByteStart,ByteSize);
+ if (RHS == 0)
+ return 0;
+
+ // X | -1 -> -1.
+ if (ConstantInt *RHSC = dyn_cast<ConstantInt>(RHS))
+ if (RHSC->isAllOnesValue())
+ return RHSC;
+
+ Constant *LHS = ExtractConstantBytes(CE->getOperand(0), ByteStart,ByteSize);
+ if (LHS == 0)
+ return 0;
+ return ConstantExpr::getOr(LHS, RHS);
+ }
+ case Instruction::And: {
+ Constant *RHS = ExtractConstantBytes(CE->getOperand(1), ByteStart,ByteSize);
+ if (RHS == 0)
+ return 0;
+
+ // X & 0 -> 0.
+ if (RHS->isNullValue())
+ return RHS;
+
+ Constant *LHS = ExtractConstantBytes(CE->getOperand(0), ByteStart,ByteSize);
+ if (LHS == 0)
+ return 0;
+ return ConstantExpr::getAnd(LHS, RHS);
+ }
+ case Instruction::LShr: {
+ ConstantInt *Amt = dyn_cast<ConstantInt>(CE->getOperand(1));
+ if (Amt == 0)
+ return 0;
+ unsigned ShAmt = Amt->getZExtValue();
+ // Cannot analyze non-byte shifts.
+ if ((ShAmt & 7) != 0)
+ return 0;
+ ShAmt >>= 3;
+
+ // If the extract is known to be all zeros, return zero.
+ if (ByteStart >= CSize-ShAmt)
+ return Constant::getNullValue(IntegerType::get(CE->getContext(),
+ ByteSize*8));
+ // If the extract is known to be fully in the input, extract it.
+ if (ByteStart+ByteSize+ShAmt <= CSize)
+ return ExtractConstantBytes(CE->getOperand(0), ByteStart+ShAmt, ByteSize);
+
+ // TODO: Handle the 'partially zero' case.
+ return 0;
+ }
+
+ case Instruction::Shl: {
+ ConstantInt *Amt = dyn_cast<ConstantInt>(CE->getOperand(1));
+ if (Amt == 0)
+ return 0;
+ unsigned ShAmt = Amt->getZExtValue();
+ // Cannot analyze non-byte shifts.
+ if ((ShAmt & 7) != 0)
+ return 0;
+ ShAmt >>= 3;
+
+ // If the extract is known to be all zeros, return zero.
+ if (ByteStart+ByteSize <= ShAmt)
+ return Constant::getNullValue(IntegerType::get(CE->getContext(),
+ ByteSize*8));
+ // If the extract is known to be fully in the input, extract it.
+ if (ByteStart >= ShAmt)
+ return ExtractConstantBytes(CE->getOperand(0), ByteStart-ShAmt, ByteSize);
+
+ // TODO: Handle the 'partially zero' case.
+ return 0;
+ }
+
+ case Instruction::ZExt: {
+ unsigned SrcBitSize =
+ cast<IntegerType>(CE->getOperand(0)->getType())->getBitWidth();
+
+ // If extracting something that is completely zero, return 0.
+ if (ByteStart*8 >= SrcBitSize)
+ return Constant::getNullValue(IntegerType::get(CE->getContext(),
+ ByteSize*8));
+
+ // If exactly extracting the input, return it.
+ if (ByteStart == 0 && ByteSize*8 == SrcBitSize)
+ return CE->getOperand(0);
+
+ // If extracting something completely in the input, if if the input is a
+ // multiple of 8 bits, recurse.
+ if ((SrcBitSize&7) == 0 && (ByteStart+ByteSize)*8 <= SrcBitSize)
+ return ExtractConstantBytes(CE->getOperand(0), ByteStart, ByteSize);
+
+ // Otherwise, if extracting a subset of the input, which is not multiple of
+ // 8 bits, do a shift and trunc to get the bits.
+ if ((ByteStart+ByteSize)*8 < SrcBitSize) {
+ assert((SrcBitSize&7) && "Shouldn't get byte sized case here");
+ Constant *Res = CE->getOperand(0);
+ if (ByteStart)
+ Res = ConstantExpr::getLShr(Res,
+ ConstantInt::get(Res->getType(), ByteStart*8));
+ return ConstantExpr::getTrunc(Res, IntegerType::get(C->getContext(),
+ ByteSize*8));
+ }
+
+ // TODO: Handle the 'partially zero' case.
+ return 0;
+ }
+ }
+}
+
+/// getFoldedSizeOf - Return a ConstantExpr with type DestTy for sizeof
+/// on Ty, with any known factors factored out. If Folded is false,
+/// return null if no factoring was possible, to avoid endlessly
+/// bouncing an unfoldable expression back into the top-level folder.
+///
+static Constant *getFoldedSizeOf(const Type *Ty, const Type *DestTy,
+ bool Folded) {
+ if (const ArrayType *ATy = dyn_cast<ArrayType>(Ty)) {
+ Constant *N = ConstantInt::get(DestTy, ATy->getNumElements());
+ Constant *E = getFoldedSizeOf(ATy->getElementType(), DestTy, true);
+ return ConstantExpr::getNUWMul(E, N);
+ }
+
+ if (const StructType *STy = dyn_cast<StructType>(Ty))
+ if (!STy->isPacked()) {
+ unsigned NumElems = STy->getNumElements();
+ // An empty struct has size zero.
+ if (NumElems == 0)
+ return ConstantExpr::getNullValue(DestTy);
+ // Check for a struct with all members having the same size.
+ Constant *MemberSize =
+ getFoldedSizeOf(STy->getElementType(0), DestTy, true);
+ bool AllSame = true;
+ for (unsigned i = 1; i != NumElems; ++i)
+ if (MemberSize !=
+ getFoldedSizeOf(STy->getElementType(i), DestTy, true)) {
+ AllSame = false;
+ break;
+ }
+ if (AllSame) {
+ Constant *N = ConstantInt::get(DestTy, NumElems);
+ return ConstantExpr::getNUWMul(MemberSize, N);
+ }
+ }
+
+ // Pointer size doesn't depend on the pointee type, so canonicalize them
+ // to an arbitrary pointee.
+ if (const PointerType *PTy = dyn_cast<PointerType>(Ty))
+ if (!PTy->getElementType()->isIntegerTy(1))
+ return
+ getFoldedSizeOf(PointerType::get(IntegerType::get(PTy->getContext(), 1),
+ PTy->getAddressSpace()),
+ DestTy, true);
+
+ // If there's no interesting folding happening, bail so that we don't create
+ // a constant that looks like it needs folding but really doesn't.
+ if (!Folded)
+ return 0;
+
+ // Base case: Get a regular sizeof expression.
+ Constant *C = ConstantExpr::getSizeOf(Ty);
+ C = ConstantExpr::getCast(CastInst::getCastOpcode(C, false,
+ DestTy, false),
+ C, DestTy);
+ return C;
+}
+
+/// getFoldedAlignOf - Return a ConstantExpr with type DestTy for alignof
+/// on Ty, with any known factors factored out. If Folded is false,
+/// return null if no factoring was possible, to avoid endlessly
+/// bouncing an unfoldable expression back into the top-level folder.
+///
+static Constant *getFoldedAlignOf(const Type *Ty, const Type *DestTy,
+ bool Folded) {
+ // The alignment of an array is equal to the alignment of the
+ // array element. Note that this is not always true for vectors.
+ if (const ArrayType *ATy = dyn_cast<ArrayType>(Ty)) {
+ Constant *C = ConstantExpr::getAlignOf(ATy->getElementType());
+ C = ConstantExpr::getCast(CastInst::getCastOpcode(C, false,
+ DestTy,
+ false),
+ C, DestTy);
+ return C;
+ }
+
+ if (const StructType *STy = dyn_cast<StructType>(Ty)) {
+ // Packed structs always have an alignment of 1.
+ if (STy->isPacked())
+ return ConstantInt::get(DestTy, 1);
+
+ // Otherwise, struct alignment is the maximum alignment of any member.
+ // Without target data, we can't compare much, but we can check to see
+ // if all the members have the same alignment.
+ unsigned NumElems = STy->getNumElements();
+ // An empty struct has minimal alignment.
+ if (NumElems == 0)
+ return ConstantInt::get(DestTy, 1);
+ // Check for a struct with all members having the same alignment.
+ Constant *MemberAlign =
+ getFoldedAlignOf(STy->getElementType(0), DestTy, true);
+ bool AllSame = true;
+ for (unsigned i = 1; i != NumElems; ++i)
+ if (MemberAlign != getFoldedAlignOf(STy->getElementType(i), DestTy, true)) {
+ AllSame = false;
+ break;
+ }
+ if (AllSame)
+ return MemberAlign;
+ }
+
+ // Pointer alignment doesn't depend on the pointee type, so canonicalize them
+ // to an arbitrary pointee.
+ if (const PointerType *PTy = dyn_cast<PointerType>(Ty))
+ if (!PTy->getElementType()->isIntegerTy(1))
+ return
+ getFoldedAlignOf(PointerType::get(IntegerType::get(PTy->getContext(),
+ 1),
+ PTy->getAddressSpace()),
+ DestTy, true);
+
+ // If there's no interesting folding happening, bail so that we don't create
+ // a constant that looks like it needs folding but really doesn't.
+ if (!Folded)
+ return 0;
+
+ // Base case: Get a regular alignof expression.
+ Constant *C = ConstantExpr::getAlignOf(Ty);
+ C = ConstantExpr::getCast(CastInst::getCastOpcode(C, false,
+ DestTy, false),
+ C, DestTy);
+ return C;
+}
+
+/// getFoldedOffsetOf - Return a ConstantExpr with type DestTy for offsetof
+/// on Ty and FieldNo, with any known factors factored out. If Folded is false,
+/// return null if no factoring was possible, to avoid endlessly
+/// bouncing an unfoldable expression back into the top-level folder.
+///
+static Constant *getFoldedOffsetOf(const Type *Ty, Constant *FieldNo,
+ const Type *DestTy,
+ bool Folded) {
+ if (const ArrayType *ATy = dyn_cast<ArrayType>(Ty)) {
+ Constant *N = ConstantExpr::getCast(CastInst::getCastOpcode(FieldNo, false,
+ DestTy, false),
+ FieldNo, DestTy);
+ Constant *E = getFoldedSizeOf(ATy->getElementType(), DestTy, true);
+ return ConstantExpr::getNUWMul(E, N);
+ }
+
+ if (const StructType *STy = dyn_cast<StructType>(Ty))
+ if (!STy->isPacked()) {
+ unsigned NumElems = STy->getNumElements();
+ // An empty struct has no members.
+ if (NumElems == 0)
+ return 0;
+ // Check for a struct with all members having the same size.
+ Constant *MemberSize =
+ getFoldedSizeOf(STy->getElementType(0), DestTy, true);
+ bool AllSame = true;
+ for (unsigned i = 1; i != NumElems; ++i)
+ if (MemberSize !=
+ getFoldedSizeOf(STy->getElementType(i), DestTy, true)) {
+ AllSame = false;
+ break;
+ }
+ if (AllSame) {
+ Constant *N = ConstantExpr::getCast(CastInst::getCastOpcode(FieldNo,
+ false,
+ DestTy,
+ false),
+ FieldNo, DestTy);
+ return ConstantExpr::getNUWMul(MemberSize, N);
+ }
+ }
+
+ // If there's no interesting folding happening, bail so that we don't create
+ // a constant that looks like it needs folding but really doesn't.
+ if (!Folded)
+ return 0;
+
+ // Base case: Get a regular offsetof expression.
+ Constant *C = ConstantExpr::getOffsetOf(Ty, FieldNo);
+ C = ConstantExpr::getCast(CastInst::getCastOpcode(C, false,
+ DestTy, false),
+ C, DestTy);
+ return C;
+}
+
+Constant *llvm::ConstantFoldCastInstruction(unsigned opc, Constant *V,