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two changes:

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1. Make instcombine always canonicalize trunc x to i1 into an icmp(x&1).  This 
   exposes the AND to other instcombine xforms and is more of what the code
   generator expects.
2. Rewrite the remaining trunc pattern match to use 'match', which 
   simplifies it a lot.
   

llvm-svn: 67635
This commit is contained in:
Chris Lattner 2009-03-24 18:15:30 +00:00
parent 68e30cdf59
commit 51a4134e1c
2 changed files with 35 additions and 44 deletions
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72
lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -6575,8 +6575,8 @@ Instruction *InstCombiner::visitICmpInstWithInstAndIntCst(ICmpInst &ICI,
// preferable because it allows the C<<Y expression to be hoisted out
// of a loop if Y is invariant and X is not.
if (Shift && Shift->hasOneUse() && RHSV == 0 &&
ICI.isEquality() && !Shift->isArithmeticShift() &&
isa<Instruction>(Shift->getOperand(0))) {
ICI.isEquality() && !Shift->isArithmeticShift()/* &&
isa<Instruction>(Shift->getOperand(0))*/) {
// Compute C << Y.
Value *NS;
if (Shift->getOpcode() == Instruction::LShr) {
@ -8147,49 +8147,33 @@ Instruction *InstCombiner::visitTrunc(TruncInst &CI) {
const Type *Ty = CI.getType();
uint32_t DestBitWidth = Ty->getPrimitiveSizeInBits();
uint32_t SrcBitWidth = cast<IntegerType>(Src->getType())->getBitWidth();
// Canonicalize trunc x to i1 -> (icmp ne (and x, 1), 0)
if (DestBitWidth == 1) {
Constant *One = ConstantInt::get(Src->getType(), 1);
Src = InsertNewInstBefore(BinaryOperator::CreateAnd(Src, One, "tmp"), CI);
Value *Zero = Constant::getNullValue(Src->getType());
return new ICmpInst(ICmpInst::ICMP_NE, Src, Zero);
}
if (Instruction *SrcI = dyn_cast<Instruction>(Src)) {
switch (SrcI->getOpcode()) {
default: break;
case Instruction::LShr:
// We can shrink lshr to something smaller if we know the bits shifted in
// are already zeros.
if (ConstantInt *ShAmtV = dyn_cast<ConstantInt>(SrcI->getOperand(1))) {
uint32_t ShAmt = ShAmtV->getLimitedValue(SrcBitWidth);
// Get a mask for the bits shifting in.
APInt Mask(APInt::getLowBitsSet(SrcBitWidth, ShAmt).shl(DestBitWidth));
Value* SrcIOp0 = SrcI->getOperand(0);
if (SrcI->hasOneUse() && MaskedValueIsZero(SrcIOp0, Mask)) {
if (ShAmt >= DestBitWidth) // All zeros.
return ReplaceInstUsesWith(CI, Constant::getNullValue(Ty));
// Okay, we can shrink this. Truncate the input, then return a new
// shift.
Value *V1 = InsertCastBefore(Instruction::Trunc, SrcIOp0, Ty, CI);
Value *V2 = InsertCastBefore(Instruction::Trunc, SrcI->getOperand(1),
Ty, CI);
return BinaryOperator::CreateLShr(V1, V2);
}
} else { // This is a variable shr.
// Turn 'trunc (lshr X, Y) to bool' into '(X & (1 << Y)) != 0'. This is
// more LLVM instructions, but allows '1 << Y' to be hoisted if
// loop-invariant and CSE'd.
if (CI.getType() == Type::Int1Ty && SrcI->hasOneUse()) {
Value *One = ConstantInt::get(SrcI->getType(), 1);
Value *V = InsertNewInstBefore(
BinaryOperator::CreateShl(One, SrcI->getOperand(1),
"tmp"), CI);
V = InsertNewInstBefore(BinaryOperator::CreateAnd(V,
SrcI->getOperand(0),
"tmp"), CI);
Value *Zero = Constant::getNullValue(V->getType());
return new ICmpInst(ICmpInst::ICMP_NE, V, Zero);
}
}
break;
// Optimize trunc(lshr(), c) to pull the shift through the truncate.
ConstantInt *ShAmtV = 0;
Value *ShiftOp = 0;
if (Src->hasOneUse() &&
match(Src, m_LShr(m_Value(ShiftOp), m_ConstantInt(ShAmtV)))) {
uint32_t ShAmt = ShAmtV->getLimitedValue(SrcBitWidth);
// Get a mask for the bits shifting in.
APInt Mask(APInt::getLowBitsSet(SrcBitWidth, ShAmt).shl(DestBitWidth));
if (MaskedValueIsZero(ShiftOp, Mask)) {
if (ShAmt >= DestBitWidth) // All zeros.
return ReplaceInstUsesWith(CI, Constant::getNullValue(Ty));
// Okay, we can shrink this. Truncate the input, then return a new
// shift.
Value *V1 = InsertCastBefore(Instruction::Trunc, ShiftOp, Ty, CI);
Value *V2 = ConstantExpr::getTrunc(ShAmtV, Ty);
return BinaryOperator::CreateLShr(V1, V2);
}
}

7
test/Transforms/InstCombine/shift.ll
View File

@ -206,4 +206,11 @@ define i32 @test26(i32 %A) {
%D = shl i32 %C, 1 ; <i32> [#uses=1]
ret i32 %D
}
define i1 @test27(i32 %x) nounwind {
%y = lshr i32 %x, 3
%z = trunc i32 %y to i1
ret i1 %z
}