/// This is a truncation operation if Ty is smaller than V->getType(), or an
/// extension operation if Ty is larger.
static bool CanEvaluateInDifferentType(Value *V, const IntegerType *Ty,
- int &NumCastsRemoved) {
+ unsigned CastOpc, int &NumCastsRemoved) {
// We can always evaluate constants in another type.
if (isa<ConstantInt>(V))
return true;
const IntegerType *OrigTy = cast<IntegerType>(V->getType());
+ // If this is an extension or truncate, we can often eliminate it.
+ if (isa<TruncInst>(I) || isa<ZExtInst>(I) || isa<SExtInst>(I)) {
+ // If this is a cast from the destination type, we can trivially eliminate
+ // it, and this will remove a cast overall.
+ if (I->getOperand(0)->getType() == Ty) {
+ // If the first operand is itself a cast, and is eliminable, do not count
+ // this as an eliminable cast. We would prefer to eliminate those two
+ // casts first.
+ if (!isa<CastInst>(I->getOperand(0)))
+ ++NumCastsRemoved;
+ return true;
+ }
+ }
+
+ // We can't extend or shrink something that has multiple uses: doing so would
+ // require duplicating the instruction in general, which isn't profitable.
+ if (!I->hasOneUse()) return false;
+
switch (I->getOpcode()) {
case Instruction::Add:
case Instruction::Sub:
case Instruction::And:
case Instruction::Or:
case Instruction::Xor:
- if (!I->hasOneUse()) return false;
// These operators can all arbitrarily be extended or truncated.
- return CanEvaluateInDifferentType(I->getOperand(0), Ty, NumCastsRemoved) &&
- CanEvaluateInDifferentType(I->getOperand(1), Ty, NumCastsRemoved);
+ return CanEvaluateInDifferentType(I->getOperand(0), Ty, CastOpc,
+ NumCastsRemoved) &&
+ CanEvaluateInDifferentType(I->getOperand(1), Ty, CastOpc,
+ NumCastsRemoved);
case Instruction::Shl:
- if (!I->hasOneUse()) return false;
// If we are truncating the result of this SHL, and if it's a shift of a
// constant amount, we can always perform a SHL in a smaller type.
if (ConstantInt *CI = dyn_cast<ConstantInt>(I->getOperand(1))) {
uint32_t BitWidth = Ty->getBitWidth();
if (BitWidth < OrigTy->getBitWidth() &&
CI->getLimitedValue(BitWidth) < BitWidth)
- return CanEvaluateInDifferentType(I->getOperand(0), Ty,NumCastsRemoved);
+ return CanEvaluateInDifferentType(I->getOperand(0), Ty, CastOpc,
+ NumCastsRemoved);
}
break;
case Instruction::LShr:
- if (!I->hasOneUse()) return false;
// If this is a truncate of a logical shr, we can truncate it to a smaller
// lshr iff we know that the bits we would otherwise be shifting in are
// already zeros.
MaskedValueIsZero(I->getOperand(0),
APInt::getHighBitsSet(OrigBitWidth, OrigBitWidth-BitWidth)) &&
CI->getLimitedValue(BitWidth) < BitWidth) {
- return CanEvaluateInDifferentType(I->getOperand(0), Ty,NumCastsRemoved);
+ return CanEvaluateInDifferentType(I->getOperand(0), Ty, CastOpc,
+ NumCastsRemoved);
}
}
break;
- case Instruction::Trunc:
case Instruction::ZExt:
case Instruction::SExt:
- // If this is a cast from the destination type, we can trivially eliminate
- // it, and this will remove a cast overall.
- if (I->getOperand(0)->getType() == Ty) {
- // If the first operand is itself a cast, and is eliminable, do not count
- // this as an eliminable cast. We would prefer to eliminate those two
- // casts first.
- if (isa<CastInst>(I->getOperand(0)))
- return true;
-
+ case Instruction::Trunc:
+ // If this is the same kind of case as our original (e.g. zext+zext), we
+ // can safely eliminate it.
+ if (I->getOpcode() == CastOpc) {
++NumCastsRemoved;
return true;
}
case Instruction::Trunc:
case Instruction::ZExt:
case Instruction::SExt:
- case Instruction::BitCast:
// If the source type of the cast is the type we're trying for then we can
- // just return the source. There's no need to insert it because its not new.
+ // just return the source. There's no need to insert it because it is not
+ // new.
if (I->getOperand(0)->getType() == Ty)
return I->getOperand(0);
- // Some other kind of cast, which shouldn't happen, so just ..
- // FALL THROUGH
+ // Otherwise, must be the same type of case, so just reinsert a new one.
+ Res = CastInst::create(cast<CastInst>(I)->getOpcode(), I->getOperand(0),
+ Ty, I->getName());
+ break;
default:
// TODO: Can handle more cases here.
assert(0 && "Unreachable!");
int NumCastsRemoved = 0;
if (!isa<BitCastInst>(CI) &&
CanEvaluateInDifferentType(SrcI, cast<IntegerType>(DestTy),
- NumCastsRemoved)) {
+ CI.getOpcode(), NumCastsRemoved)) {
// If this cast is a truncate, evaluting in a different type always
- // eliminates the cast, so it is always a win. If this is a noop-cast
- // this just removes a noop cast which isn't pointful, but simplifies
- // the code. If this is a zero-extension, we need to do an AND to
- // maintain the clear top-part of the computation, so we require that
- // the input have eliminated at least one cast. If this is a sign
- // extension, we insert two new casts (to do the extension) so we
+ // eliminates the cast, so it is always a win. If this is a zero-extension,
+ // we need to do an AND to maintain the clear top-part of the computation,
+ // so we require that the input have eliminated at least one cast. If this
+ // is a sign extension, we insert two new casts (to do the extension) so we
// require that two casts have been eliminated.
bool DoXForm;
switch (CI.getOpcode()) {
case Instruction::SExt:
DoXForm = NumCastsRemoved >= 2;
break;
- case Instruction::BitCast:
- DoXForm = false;
- break;
}
if (DoXForm) {
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