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Revert trunc(lshr (sext A), Cst) to ashr A, Cst

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This reverts commit r246997, it introduced a regression (PR24763).

llvm-svn: 247180
This commit is contained in:
David Majnemer 2015-09-09 20:20:08 +00:00
parent acd97a51fe
commit 3926c488cf
2 changed files with 0 additions and 57 deletions
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20
lib/Transforms/InstCombine/InstCombineCasts.cpp
View File

@ -498,26 +498,6 @@ Instruction *InstCombiner::visitTrunc(TruncInst &CI) {
return CastInst::CreateIntegerCast(Shift, CI.getType(), false);
}
// Transform trunc(lshr (sext A), Cst) to ashr A, Cst to eliminate type
// conversion.
// It works because bits coming from sign extension have the same value as
// sign bit of the original value; performing ashr instead of lshr
// generates bits of the same value as the sign bit.
if (Src->hasOneUse() &&
match(Src, m_LShr(m_SExt(m_Value(A)), m_ConstantInt(Cst))) &&
cast<Instruction>(Src)->getOperand(0)->hasOneUse()) {
const unsigned ASize = A->getType()->getPrimitiveSizeInBits();
// This optimization can be only performed when zero bits generated by
// the original lshr aren't pulled into the value after truncation, so we
// can only shift by values smaller then the size of destination type (in
// bits).
if (Cst->getValue().ult(ASize)) {
Value *Shift = Builder->CreateAShr(A, Cst->getZExtValue());
Shift->takeName(Src);
return CastInst::CreateIntegerCast(Shift, CI.getType(), false);
}
}
// Transform "trunc (and X, cst)" -> "and (trunc X), cst" so long as the dest
// type isn't non-native.
if (Src->hasOneUse() && isa<IntegerType>(Src->getType()) &&

37
test/Transforms/InstCombine/cast.ll
View File

@ -1062,43 +1062,6 @@ define i8 @test85(i32 %a) {
; CHECK: [[CST:%.*]] = trunc i32 [[SHR]] to i8
}
define i16 @test86(i16 %v) {
%a = sext i16 %v to i32
%s = ashr i32 %a, 4
%t = trunc i32 %s to i16
ret i16 %t
; CHECK-LABEL: @test86(
; CHECK: [[ASHR:%.*]] = ashr i16 %v, 4
; CHECK-NEXT: ret i16 [[ASHR]]
}
define i16 @test87(i16 %v) {
%c = sext i16 %v to i32
%m = mul nsw i32 %c, 16
%a = ashr i32 %m, 16
%t = trunc i32 %a to i16
ret i16 %t
; CHECK-LABEL: @test87(
; CHECK: [[ASHR:%.*]] = ashr i16 %v, 12
; CHECK-NEXT: ret i16 [[ASHR]]
}
define i16 @test88(i16 %v) {
%a = sext i16 %v to i32
%s = ashr i32 %a, 18
%t = trunc i32 %s to i16
ret i16 %t
; Do not optimize to ashr i16 (shift by 18)
; CHECK-LABEL: @test88(
; CHECK: [[SEXT:%.*]] = sext i16 %v to i32
; CHECK-NEXT: [[ASHR:%.*]] = ashr i32 [[SEXT]], 18
; CHECK-NEXT: [[TRUNC:%.*]] = trunc i32 [[ASHR]] to i16
; CHECK-NEXT: ret i16 [[TRUNC]]
}
; Overflow on a float to int or int to float conversion is undefined (PR21130).
define i8 @overflow_fptosi() {