[llvm-commits] [llvm] r136435 - in /llvm/trunk: lib/Transforms/InstCombine/InstCombineShifts.cpp test/Transforms/InstCombine/shift.ll

[Nick Lewycky]

Eli Friedman wrote:
> Author: efriedma
> Date: Thu Jul 28 19:18:19 2011
> New Revision: 136435
>
> URL: http://llvm.org/viewvc/llvm-project?rev=136435&view=rev
> Log:
> Make sure to correctly clear the exact/nuw/nsw flags off of shifts when they are combined together.<rdar://problem/9859829>

Maybe I'm missing something, but isn't it safe to preserve the 
intersection of the flags on a chain of same-directional shifts? I'm 
pretty sure it's safe.

Nick

>
>
> Modified:
>      llvm/trunk/lib/Transforms/InstCombine/InstCombineShifts.cpp
>      llvm/trunk/test/Transforms/InstCombine/shift.ll
>
> Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineShifts.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineShifts.cpp?rev=136435&r1=136434&r2=136435&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Transforms/InstCombine/InstCombineShifts.cpp (original)
> +++ llvm/trunk/lib/Transforms/InstCombine/InstCombineShifts.cpp Thu Jul 28 19:18:19 2011
> @@ -208,11 +208,12 @@
>       return I;
>
>     case Instruction::Shl: {
> -    unsigned TypeWidth = I->getType()->getScalarSizeInBits();
> +    BinaryOperator *BO = cast<BinaryOperator>(I);
> +    unsigned TypeWidth = BO->getType()->getScalarSizeInBits();
>
>       // We only accept shifts-by-a-constant in CanEvaluateShifted.
> -    ConstantInt *CI = cast<ConstantInt>(I->getOperand(1));
> -
> +    ConstantInt *CI = cast<ConstantInt>(BO->getOperand(1));
> +
>       // We can always fold shl(c1)+shl(c2) ->  shl(c1+c2).
>       if (isLeftShift) {
>         // If this is oversized composite shift, then unsigned shifts get 0.
> @@ -220,7 +221,9 @@
>         if (NewShAmt>= TypeWidth)
>           return Constant::getNullValue(I->getType());
>
> -      I->setOperand(1, ConstantInt::get(I->getType(), NewShAmt));
> +      BO->setOperand(1, ConstantInt::get(BO->getType(), NewShAmt));
> +      BO->setHasNoUnsignedWrap(false);
> +      BO->setHasNoSignedWrap(false);
>         return I;
>       }
>
> @@ -228,11 +231,11 @@
>       // zeros.
>       if (CI->getValue() == NumBits) {
>         APInt Mask(APInt::getLowBitsSet(TypeWidth, TypeWidth - NumBits));
> -      V = IC.Builder->CreateAnd(I->getOperand(0),
> -                                ConstantInt::get(I->getContext(), Mask));
> +      V = IC.Builder->CreateAnd(BO->getOperand(0),
> +                                ConstantInt::get(BO->getContext(), Mask));
>         if (Instruction *VI = dyn_cast<Instruction>(V)) {
> -        VI->moveBefore(I);
> -        VI->takeName(I);
> +        VI->moveBefore(BO);
> +        VI->takeName(BO);
>         }
>         return V;
>       }
> @@ -240,23 +243,27 @@
>       // We turn shl(c1)+shr(c2) ->  shl(c3)+and(c4), but only when we know that
>       // the and won't be needed.
>       assert(CI->getZExtValue()>  NumBits);
> -    I->setOperand(1, ConstantInt::get(I->getType(),
> -                                      CI->getZExtValue() - NumBits));
> -    return I;
> +    BO->setOperand(1, ConstantInt::get(BO->getType(),
> +                                       CI->getZExtValue() - NumBits));
> +    BO->setHasNoUnsignedWrap(false);
> +    BO->setHasNoSignedWrap(false);
> +    return BO;
>     }
>     case Instruction::LShr: {
> -    unsigned TypeWidth = I->getType()->getScalarSizeInBits();
> +    BinaryOperator *BO = cast<BinaryOperator>(I);
> +    unsigned TypeWidth = BO->getType()->getScalarSizeInBits();
>       // We only accept shifts-by-a-constant in CanEvaluateShifted.
> -    ConstantInt *CI = cast<ConstantInt>(I->getOperand(1));
> +    ConstantInt *CI = cast<ConstantInt>(BO->getOperand(1));
>
>       // We can always fold lshr(c1)+lshr(c2) ->  lshr(c1+c2).
>       if (!isLeftShift) {
>         // If this is oversized composite shift, then unsigned shifts get 0.
>         unsigned NewShAmt = NumBits+CI->getZExtValue();
>         if (NewShAmt>= TypeWidth)
> -        return Constant::getNullValue(I->getType());
> +        return Constant::getNullValue(BO->getType());
>
> -      I->setOperand(1, ConstantInt::get(I->getType(), NewShAmt));
> +      BO->setOperand(1, ConstantInt::get(BO->getType(), NewShAmt));
> +      BO->setIsExact(false);
>         return I;
>       }
>
> @@ -265,7 +272,7 @@
>       if (CI->getValue() == NumBits) {
>         APInt Mask(APInt::getHighBitsSet(TypeWidth, TypeWidth - NumBits));
>         V = IC.Builder->CreateAnd(I->getOperand(0),
> -                                ConstantInt::get(I->getContext(), Mask));
> +                                ConstantInt::get(BO->getContext(), Mask));
>         if (Instruction *VI = dyn_cast<Instruction>(V)) {
>           VI->moveBefore(I);
>           VI->takeName(I);
> @@ -276,9 +283,10 @@
>       // We turn lshr(c1)+shl(c2) ->  lshr(c3)+and(c4), but only when we know that
>       // the and won't be needed.
>       assert(CI->getZExtValue()>  NumBits);
> -    I->setOperand(1, ConstantInt::get(I->getType(),
> -                                      CI->getZExtValue() - NumBits));
> -    return I;
> +    BO->setOperand(1, ConstantInt::get(BO->getType(),
> +                                       CI->getZExtValue() - NumBits));
> +    BO->setIsExact(false);
> +    return BO;
>     }
>
>     case Instruction::Select:
>
> Modified: llvm/trunk/test/Transforms/InstCombine/shift.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/shift.ll?rev=136435&r1=136434&r2=136435&view=diff
> ==============================================================================
> --- llvm/trunk/test/Transforms/InstCombine/shift.ll (original)
> +++ llvm/trunk/test/Transforms/InstCombine/shift.ll Thu Jul 28 19:18:19 2011
> @@ -525,5 +525,20 @@
>   ; CHECK-NEXT: ret
>   }
>
> +define i32 @test44(i32 %a) nounwind {
> +  %y = shl nuw i32 %a, 1
> +  %z = shl i32 %y, 4
> +  ret i32 %z
> +; CHECK: @test44
> +; CHECK-NEXT: %y = shl i32 %a, 5
> +; CHECK-NEXT: ret i32 %y
> +}
>
> -
> +define i32 @test45(i32 %a) nounwind {
> +  %y = lshr exact i32 %a, 1
> +  %z = lshr i32 %y, 4
> +  ret i32 %z
> +; CHECK: @test45
> +; CHECK-NEXT: %y = lshr i32 %a, 5
> +; CHECK-NEXT: ret i32 %y
> +}
>
>
> _______________________________________________
> llvm-commits mailing list
> llvm-commits at cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
>