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my instcombine transformations to make extension elimination more

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aggressive changed the canonical form from sext(trunc(x)) to ashr(lshr(x)),
make sure to transform a couple more things into that canonical form,
and catch a case where we missed turning zext/shl/ashr into a single sext.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@93787 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2010-01-18 22:19:16 +00:00
parent 2122f69c02
commit cd5adbbc0c
3 changed files with 47 additions and 11 deletions
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13
lib/Transforms/InstCombine/InstCombineCasts.cpp
View File

@ -955,6 +955,19 @@ Instruction *InstCombiner::visitSExt(SExtInst &CI) {
ShAmt);
}
// If this input is a trunc from our destination, then turn sext(trunc(x))
// into shifts.
if (TruncInst *TI = dyn_cast<TruncInst>(Src))
if (TI->hasOneUse() && TI->getOperand(0)->getType() == DestTy) {
uint32_t SrcBitSize = SrcTy->getScalarSizeInBits();
uint32_t DestBitSize = DestTy->getScalarSizeInBits();
// We need to emit a shl + ashr to do the sign extend.
Value *ShAmt = ConstantInt::get(DestTy, DestBitSize-SrcBitSize);
Value *Res = Builder->CreateShl(TI->getOperand(0), ShAmt, "sext");
return BinaryOperator::CreateAShr(Res, ShAmt);
}
// If the input is a shl/ashr pair of a same constant, then this is a sign
// extension from a smaller value. If we could trust arbitrary bitwidth
// integers, we could turn this into a truncate to the smaller bit and then

24
lib/Transforms/InstCombine/InstCombineShifts.cpp
View File

@ -404,12 +404,26 @@ Instruction *InstCombiner::visitAShr(BinaryOperator &I) {
if (ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
// If the input is a SHL by the same constant (ashr (shl X, C), C), then we
// have a sign-extend idiom. If the input value is known to already be sign
// extended enough, delete the extension.
// have a sign-extend idiom.
Value *X;
if (match(Op0, m_Shl(m_Value(X), m_Specific(Op1))) &&
ComputeNumSignBits(X) > Op1C->getZExtValue())
return ReplaceInstUsesWith(I, X);
if (match(Op0, m_Shl(m_Value(X), m_Specific(Op1)))) {
// If the input value is known to already be sign extended enough, delete
// the extension.
if (ComputeNumSignBits(X) > Op1C->getZExtValue())
return ReplaceInstUsesWith(I, X);
// If the input is an extension from the shifted amount value, e.g.
// %x = zext i8 %A to i32
// %y = shl i32 %x, 24
// %z = ashr %y, 24
// then turn this into "z = sext i8 A to i32".
if (ZExtInst *ZI = dyn_cast<ZExtInst>(X)) {
uint32_t SrcBits = ZI->getOperand(0)->getType()->getScalarSizeInBits();
uint32_t DestBits = ZI->getType()->getScalarSizeInBits();
if (Op1C->getZExtValue() == DestBits-SrcBits)
return new SExtInst(ZI->getOperand(0), ZI->getType());
}
}
}
// See if we can turn a signed shr into an unsigned shr.

21
test/Transforms/InstCombine/signext.ll
View File

@ -8,8 +8,8 @@ define i32 @test1(i32 %x) {
%tmp.3 = add i32 %tmp.2, 32768 ; <i32> [#uses=1]
ret i32 %tmp.3
; CHECK: @test1
; CHECK: %sext = trunc i32 %x to i16
; CHECK: %tmp.3 = sext i16 %sext to i32
; CHECK: %sext1 = shl i32 %x, 16
; CHECK: %tmp.3 = ashr i32 %sext1, 16
; CHECK: ret i32 %tmp.3
}
@ -19,8 +19,8 @@ define i32 @test2(i32 %x) {
%tmp.3 = add i32 %tmp.2, -32768 ; <i32> [#uses=1]
ret i32 %tmp.3
; CHECK: @test2
; CHECK: %sext = trunc i32 %x to i16
; CHECK: %tmp.3 = sext i16 %sext to i32
; CHECK: %sext1 = shl i32 %x, 16
; CHECK: %tmp.3 = ashr i32 %sext1, 16
; CHECK: ret i32 %tmp.3
}
@ -50,8 +50,8 @@ define i32 @test5(i32 %x) {
%tmp.3 = add i32 %tmp.2, -128 ; <i32> [#uses=1]
ret i32 %tmp.3
; CHECK: @test5
; CHECK: %sext = trunc i32 %x to i8
; CHECK: %tmp.3 = sext i8 %sext to i32
; CHECK: %sext1 = shl i32 %x, 24
; CHECK: %tmp.3 = ashr i32 %sext1, 24
; CHECK: ret i32 %tmp.3
}
@ -65,3 +65,12 @@ define i32 @test6(i32 %x) {
; CHECK: ret i32 %tmp.4
}
define i32 @test7(i16 %P) {
%tmp.1 = zext i16 %P to i32 ; <i32> [#uses=1]
%sext1 = shl i32 %tmp.1, 16 ; <i32> [#uses=1]
%tmp.5 = ashr i32 %sext1, 16 ; <i32> [#uses=1]
ret i32 %tmp.5
; CHECK: @test7
; CHECK: %tmp.5 = sext i16 %P to i32
; CHECK: ret i32 %tmp.5
}