return CastInst::CreateIntegerCast(Shift, DestTy, false);
}
+ // FIXME: We should canonicalize to zext/trunc and remove this transform.
// 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
Value *SExt = cast<Instruction>(Src)->getOperand(0);
const unsigned SExtSize = SExt->getType()->getPrimitiveSizeInBits();
const unsigned ASize = A->getType()->getPrimitiveSizeInBits();
+ const unsigned CISize = CI.getType()->getPrimitiveSizeInBits();
+ const unsigned MaxAmt = SExtSize - std::max(CISize, ASize);
unsigned ShiftAmt = Cst->getZExtValue();
+
// 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 no larger than the number of extension bits.
// FIXME: Instead of bailing when the shift is too large, use and to clear
// the extra bits.
- if (SExt->hasOneUse() && ShiftAmt <= SExtSize - ASize) {
- // If shifting by the size of the original value in bits or more, it is
- // being filled with the sign bit, so shift by ASize-1 to avoid ub.
- Value *Shift = Builder->CreateAShr(A, std::min(ShiftAmt, ASize-1));
- Shift->takeName(Src);
- return CastInst::CreateIntegerCast(Shift, CI.getType(), true);
+ if (ShiftAmt <= MaxAmt) {
+ if (CISize == ASize)
+ return BinaryOperator::CreateAShr(A, ConstantInt::get(CI.getType(),
+ std::min(ShiftAmt, ASize - 1)));
+ if (SExt->hasOneUse()) {
+ Value *Shift = Builder->CreateAShr(A, std::min(ShiftAmt, ASize-1));
+ Shift->takeName(Src);
+ return CastInst::CreateIntegerCast(Shift, CI.getType(), true);
+ }
}
}
define i8 @pr33078_4(i3 %x) {
; Don't turn this in an `ashr`. This was getting miscompiled
; CHECK-LABEL: @pr33078_4(
-; CHECK-NEXT: [[C:%.*]] = ashr i3 %x, 2
-; CHECK-NEXT: [[B:%.*]] = sext i3 [[C]] to i8
+; CHECK-NEXT: [[B:%.*]] = sext i3 %x to i16
+; CHECK-NEXT: [[C:%.*]] = lshr i16 [[B]], 13
+; CHECK-NEXT: [[D:%.*]] = trunc i16 [[C]] to i8
; CHECK-NEXT: ret i8 [[D]]
%B = sext i3 %x to i16
%C = lshr i16 %B, 13