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commit a tweaked version of Daniel's patch for PR3599. We now

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eliminate all the extensions and all but the one required truncate
from the testcase, but the or/and/shift stuff still isn't zapped.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@64809 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2009-02-17 20:47:23 +00:00
parent 189c6357a1
commit a84f47c3e7
2 changed files with 52 additions and 26 deletions
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55
lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -8271,32 +8271,35 @@ Instruction *InstCombiner::visitZExt(ZExtInst &CI) {
Value *Src = CI.getOperand(0);
// If this is a cast of a cast
if (CastInst *CSrc = dyn_cast<CastInst>(Src)) { // A->B->C cast
// If this is a TRUNC followed by a ZEXT then we are dealing with integral
// types and if the sizes are just right we can convert this into a logical
// 'and' which will be much cheaper than the pair of casts.
if (isa<TruncInst>(CSrc)) {
// Get the sizes of the types involved
Value *A = CSrc->getOperand(0);
uint32_t SrcSize = A->getType()->getPrimitiveSizeInBits();
uint32_t MidSize = CSrc->getType()->getPrimitiveSizeInBits();
uint32_t DstSize = CI.getType()->getPrimitiveSizeInBits();
// If we're actually extending zero bits and the trunc is a no-op
if (MidSize < DstSize && SrcSize == DstSize) {
// Replace both of the casts with an And of the type mask.
APInt AndValue(APInt::getLowBitsSet(SrcSize, MidSize));
Constant *AndConst = ConstantInt::get(AndValue);
Instruction *And =
BinaryOperator::CreateAnd(CSrc->getOperand(0), AndConst);
// Unfortunately, if the type changed, we need to cast it back.
if (And->getType() != CI.getType()) {
And->setName(CSrc->getName()+".mask");
InsertNewInstBefore(And, CI);
And = CastInst::CreateIntegerCast(And, CI.getType(), false/*ZExt*/);
}
return And;
}
// If this is a TRUNC followed by a ZEXT then we are dealing with integral
// types and if the sizes are just right we can convert this into a logical
// 'and' which will be much cheaper than the pair of casts.
if (TruncInst *CSrc = dyn_cast<TruncInst>(Src)) { // A->B->C cast
// Get the sizes of the types involved. We know that the intermediate type
// will be smaller than A or C, but don't know the relation between A and C.
Value *A = CSrc->getOperand(0);
unsigned SrcSize = A->getType()->getPrimitiveSizeInBits();
unsigned MidSize = CSrc->getType()->getPrimitiveSizeInBits();
unsigned DstSize = CI.getType()->getPrimitiveSizeInBits();
// If we're actually extending zero bits, then if
// SrcSize < DstSize: zext(a & mask)
// SrcSize == DstSize: a & mask
// SrcSize > DstSize: trunc(a) & mask
if (SrcSize < DstSize) {
APInt AndValue(APInt::getLowBitsSet(SrcSize, MidSize));
Constant *AndConst = ConstantInt::get(AndValue);
Instruction *And =
BinaryOperator::CreateAnd(A, AndConst, CSrc->getName()+".mask");
InsertNewInstBefore(And, CI);
return new ZExtInst(And, CI.getType());
} else if (SrcSize == DstSize) {
APInt AndValue(APInt::getLowBitsSet(SrcSize, MidSize));
return BinaryOperator::CreateAnd(A, ConstantInt::get(AndValue));
} else if (SrcSize > DstSize) {
Instruction *Trunc = new TruncInst(A, CI.getType(), "tmp");
InsertNewInstBefore(Trunc, CI);
APInt AndValue(APInt::getLowBitsSet(DstSize, MidSize));
return BinaryOperator::CreateAnd(Trunc, ConstantInt::get(AndValue));
}
}

23
test/Transforms/InstCombine/zext.ll
View File

@ -8,3 +8,26 @@ define i64 @test_sext_zext(i16 %A) {
ret i64 %c2
}
; PR3599
define i32 @test2(i64 %tmp) nounwind readnone {
entry:
%tmp5 = trunc i64 %tmp to i8 ; <i8> [#uses=1]
%tmp7 = lshr i64 %tmp, 8 ; <i64> [#uses=1]
%tmp8 = trunc i64 %tmp7 to i8 ; <i8> [#uses=1]
%tmp10 = lshr i64 %tmp, 16 ; <i64> [#uses=1]
%tmp11 = trunc i64 %tmp10 to i8 ; <i8> [#uses=1]
%tmp13 = lshr i64 %tmp, 24 ; <i64> [#uses=1]
%tmp14 = trunc i64 %tmp13 to i8 ; <i8> [#uses=1]
%tmp1 = zext i8 %tmp5 to i32 ; <i32> [#uses=1]
%tmp2 = zext i8 %tmp8 to i32 ; <i32> [#uses=1]
%tmp3 = shl i32 %tmp2, 8 ; <i32> [#uses=1]
%tmp4 = zext i8 %tmp11 to i32 ; <i32> [#uses=1]
%tmp6 = shl i32 %tmp4, 16 ; <i32> [#uses=1]
%tmp9 = zext i8 %tmp14 to i32 ; <i32> [#uses=1]
%tmp12 = shl i32 %tmp9, 24 ; <i32> [#uses=1]
%tmp15 = or i32 %tmp12, %tmp1 ; <i32> [#uses=1]
%tmp16 = or i32 %tmp15, %tmp6 ; <i32> [#uses=1]
%tmp17 = or i32 %tmp16, %tmp3 ; <i32> [#uses=1]
ret i32 %tmp17
}