diff options
| -rw-r--r-- | lib/Transforms/InstCombine/InstCombineShifts.cpp | 16 | ||||
| -rw-r--r-- | test/Transforms/InstCombine/shift.ll | 18 |
2 files changed, 29 insertions, 5 deletions
diff --git a/lib/Transforms/InstCombine/InstCombineShifts.cpp b/lib/Transforms/InstCombine/InstCombineShifts.cpp index 702e0f2ee8..6779e4076c 100644 --- a/lib/Transforms/InstCombine/InstCombineShifts.cpp +++ b/lib/Transforms/InstCombine/InstCombineShifts.cpp @@ -536,12 +536,11 @@ Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, ConstantInt *Op1, if (ShiftAmt1 == 0) return 0; // Will be simplified in the future. Value *X = ShiftOp->getOperand(0); - uint32_t AmtSum = ShiftAmt1+ShiftAmt2; // Fold into one big shift. - IntegerType *Ty = cast<IntegerType>(I.getType()); // Check for (X << c1) << c2 and (X >> c1) >> c2 if (I.getOpcode() == ShiftOp->getOpcode()) { + uint32_t AmtSum = ShiftAmt1+ShiftAmt2; // Fold into one big shift. // If this is oversized composite shift, then unsigned shifts get 0, ashr // saturates. if (AmtSum >= TypeBits) { @@ -603,9 +602,16 @@ Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, ConstantInt *Op1, // (X >>? C1) << C2 --> X >>? (C1-C2) & (-1 << C2) if (I.getOpcode() == Instruction::Shl && ShiftOp->getOpcode() != Instruction::Shl) { - Value *Shift = Builder->CreateBinOp(ShiftOp->getOpcode(), X, - ConstantInt::get(Ty, ShiftDiff)); - + ConstantInt *ShiftDiffCst = ConstantInt::get(Ty, ShiftDiff); + if (ShiftOp->isExact()) { + // (X >>?exact C1) << C2 --> X >>?exact (C1-C2) + BinaryOperator *NewShr = BinaryOperator::Create(ShiftOp->getOpcode(), + X, ShiftDiffCst); + NewShr->setIsExact(true); + return NewShr; + } + Value *Shift = Builder->CreateBinOp(ShiftOp->getOpcode(), + X, ShiftDiffCst); APInt Mask(APInt::getHighBitsSet(TypeBits, TypeBits - ShiftAmt2)); return BinaryOperator::CreateAnd(Shift, ConstantInt::get(I.getContext(),Mask)); diff --git a/test/Transforms/InstCombine/shift.ll b/test/Transforms/InstCombine/shift.ll index 132d51a660..0dd969b8c0 100644 --- a/test/Transforms/InstCombine/shift.ll +++ b/test/Transforms/InstCombine/shift.ll @@ -542,3 +542,21 @@ define i32 @test45(i32 %a) nounwind { ; CHECK-NEXT: %y = lshr i32 %a, 5 ; CHECK-NEXT: ret i32 %y } + +define i32 @test46(i32 %a) { + %y = ashr exact i32 %a, 3 + %z = shl i32 %y, 1 + ret i32 %z +; CHECK: @test46 +; CHECK-NEXT: %z = ashr exact i32 %a, 2 +; CHECK-NEXT: ret i32 %z +} + +define i32 @test47(i32 %a) { + %y = lshr exact i32 %a, 3 + %z = shl i32 %y, 1 + ret i32 %z +; CHECK: @test47 +; CHECK-NEXT: %z = lshr exact i32 %a, 2 +; CHECK-NEXT: ret i32 %z +} |