// If the input is a trunc from the destination type, then turn sext(trunc(x))
// into shifts.
Value *X;
- if (match(Src, m_OneUse(m_Trunc(m_Value(X)))) && X->getType() == DestTy) {
- // sext(trunc(X)) --> ashr(shl(X, C), C)
+ if (match(Src, m_Trunc(m_Value(X)))) {
unsigned SrcBitSize = SrcTy->getScalarSizeInBits();
unsigned DestBitSize = DestTy->getScalarSizeInBits();
- Constant *ShAmt = ConstantInt::get(DestTy, DestBitSize - SrcBitSize);
- return BinaryOperator::CreateAShr(Builder.CreateShl(X, ShAmt), ShAmt);
+ unsigned XBitSize = X->getType()->getScalarSizeInBits();
+
+ // Iff X had more sign bits than the number of bits that were chopped off
+ // by the truncation, we can directly sign-extend the X.
+ unsigned XNumSignBits = ComputeNumSignBits(X, 0, &CI);
+ if (XNumSignBits > (XBitSize - SrcBitSize))
+ return CastInst::Create(Instruction::SExt, X, DestTy);
+
+ if (Src->hasOneUse() && X->getType() == DestTy) {
+ // sext(trunc(X)) --> ashr(shl(X, C), C)
+ Constant *ShAmt = ConstantInt::get(DestTy, DestBitSize - SrcBitSize);
+ return BinaryOperator::CreateAShr(Builder.CreateShl(X, ShAmt), ShAmt);
+ }
}
if (ICmpInst *ICI = dyn_cast<ICmpInst>(Src))
; CHECK-LABEL: @t0(
; CHECK-NEXT: [[A:%.*]] = ashr i8 [[X:%.*]], 5
; CHECK-NEXT: call void @use8(i8 [[A]])
-; CHECK-NEXT: [[B:%.*]] = trunc i8 [[A]] to i4
-; CHECK-NEXT: [[C:%.*]] = sext i4 [[B]] to i16
+; CHECK-NEXT: [[C:%.*]] = sext i8 [[A]] to i16
; CHECK-NEXT: ret i16 [[C]]
;
%a = ashr i8 %x, 5
; CHECK-LABEL: @t1(
; CHECK-NEXT: [[A:%.*]] = ashr i8 [[X:%.*]], 4
; CHECK-NEXT: call void @use8(i8 [[A]])
-; CHECK-NEXT: [[B:%.*]] = trunc i8 [[A]] to i4
-; CHECK-NEXT: [[C:%.*]] = sext i4 [[B]] to i16
+; CHECK-NEXT: [[C:%.*]] = sext i8 [[A]] to i16
; CHECK-NEXT: ret i16 [[C]]
;
%a = ashr i8 %x, 4
; CHECK-LABEL: @t3_vec(
; CHECK-NEXT: [[A:%.*]] = ashr <2 x i8> [[X:%.*]], <i8 4, i8 4>
; CHECK-NEXT: call void @usevec(<2 x i8> [[A]])
-; CHECK-NEXT: [[B:%.*]] = trunc <2 x i8> [[A]] to <2 x i4>
-; CHECK-NEXT: [[C:%.*]] = sext <2 x i4> [[B]] to <2 x i16>
+; CHECK-NEXT: [[C:%.*]] = sext <2 x i8> [[A]] to <2 x i16>
; CHECK-NEXT: ret <2 x i16> [[C]]
;
%a = ashr <2 x i8> %x, <i8 4, i8 4>
; CHECK-NEXT: call void @use8(i8 [[A]])
; CHECK-NEXT: [[B:%.*]] = trunc i8 [[A]] to i4
; CHECK-NEXT: call void @use4(i4 [[B]])
-; CHECK-NEXT: [[C:%.*]] = sext i4 [[B]] to i16
+; CHECK-NEXT: [[C:%.*]] = sext i8 [[A]] to i16
; CHECK-NEXT: ret i16 [[C]]
;
%a = ashr i8 %x, 5