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Simplify/generalize the xor+add->sign-extend instcombine.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@94943 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Eli Friedman
2010-01-31 04:29:12 +00:00
parent 694488f477
commit be7cfa6033
2 changed files with 36 additions and 41 deletions
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lib/Transforms/InstCombine/InstCombineAddSub.cpp
+19 -35
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@@ -121,42 +121,26 @@ Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
match(LHS, m_Xor(m_Value(XorLHS), m_ConstantInt(XorRHS)))) {
uint32_t TySizeBits = I.getType()->getScalarSizeInBits();
const APInt& RHSVal = cast<ConstantInt>(RHSC)->getValue();
uint32_t Size = TySizeBits / 2;
APInt C0080Val(APInt(TySizeBits, 1ULL).shl(Size - 1));
APInt CFF80Val(-C0080Val);
do {
if (TySizeBits > Size) {
// If we have ADD(XOR(AND(X, 0xFF), 0x80), 0xF..F80), it's a sext.
// If we have ADD(XOR(AND(X, 0xFF), 0xF..F80), 0x80), it's a sext.
if ((RHSVal == CFF80Val && XorRHS->getValue() == C0080Val) ||
(RHSVal == C0080Val && XorRHS->getValue() == CFF80Val)) {
// This is a sign extend if the top bits are known zero.
if (!MaskedValueIsZero(XorLHS,
APInt::getHighBitsSet(TySizeBits, TySizeBits - Size)))
Size = 0; // Not a sign ext, but can't be any others either.
break;
}
}
Size >>= 1;
C0080Val = APIntOps::lshr(C0080Val, Size);
CFF80Val = APIntOps::ashr(CFF80Val, Size);
} while (Size >= 1);
// FIXME: This shouldn't be necessary. When the backends can handle types
// with funny bit widths then this switch statement should be removed. It
// is just here to get the size of the "middle" type back up to something
// that the back ends can handle.
const Type *MiddleType = 0;
switch (Size) {
default: break;
case 32:
case 16:
case 8: MiddleType = IntegerType::get(I.getContext(), Size); break;
unsigned ExtendAmt = 0;
// If we have ADD(XOR(AND(X, 0xFF), 0x80), 0xF..F80), it's a sext.
// If we have ADD(XOR(AND(X, 0xFF), 0xF..F80), 0x80), it's a sext.
if (XorRHS->getValue() == -RHSVal) {
if (RHSVal.isPowerOf2())
ExtendAmt = TySizeBits - RHSVal.logBase2() - 1;
else if (XorRHS->getValue().isPowerOf2())
ExtendAmt = TySizeBits - XorRHS->getValue().logBase2() - 1;
}
if (MiddleType) {
Value *NewTrunc = Builder->CreateTrunc(XorLHS, MiddleType, "sext");
return new SExtInst(NewTrunc, I.getType(), I.getName());
if (ExtendAmt) {
APInt Mask = APInt::getHighBitsSet(TySizeBits, ExtendAmt);
if (!MaskedValueIsZero(XorLHS, Mask))
ExtendAmt = 0;
}
if (ExtendAmt) {
Constant *ShAmt = ConstantInt::get(I.getType(), ExtendAmt);
Value *NewShl = Builder->CreateShl(XorLHS, ShAmt, "sext");
return BinaryOperator::CreateAShr(NewShl, ShAmt);
}
}
}