[llvm] r174156 - Revert r174152. The shift amount may overflow and in that case this transformation is illegal.

[David Blaikie]

On Thu, Jan 31, 2013 at 11:59 PM, Nadav Rotem <nrotem at apple.com> wrote:
> Author: nadav
> Date: Fri Feb  1 01:59:33 2013
> New Revision: 174156
>
> URL: http://llvm.org/viewvc/llvm-project?rev=174156&view=rev
> Log:
> Revert r174152. The shift amount may overflow and in that case this transformation is illegal.

Do we have a test case to ensure that such an illegal transformation
does not occur?

>
> 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=174156&r1=174155&r2=174156&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Transforms/InstCombine/InstCombineShifts.cpp (original)
> +++ llvm/trunk/lib/Transforms/InstCombine/InstCombineShifts.cpp Fri Feb  1 01:59:33 2013
> @@ -709,12 +709,6 @@ Instruction *InstCombiner::visitShl(Bina
>        match(I.getOperand(1), m_Constant(C2)))
>      return BinaryOperator::CreateShl(ConstantExpr::getShl(C1, C2), A);
>
> -  // shl (c1 , add(y , c2)) -> (shl (shl(c1, c2)), y)
> -  if (match(I.getOperand(0), m_Constant(C1)) &&
> -      match(I.getOperand(1), m_Add(m_Value(A), m_Constant(C2)))) {
> -    return BinaryOperator::CreateShl(ConstantExpr::getShl(C1, C2), A);
> -  }
> -
>    return 0;
>  }
>
>
> Modified: llvm/trunk/test/Transforms/InstCombine/shift.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/shift.ll?rev=174156&r1=174155&r2=174156&view=diff
> ==============================================================================
> --- llvm/trunk/test/Transforms/InstCombine/shift.ll (original)
> +++ llvm/trunk/test/Transforms/InstCombine/shift.ll Fri Feb  1 01:59:33 2013
> @@ -745,23 +745,3 @@ define i32 @test62(i32 %x) {
>  ; CHECK: @test62
>  ; CHECK: ashr exact i32 %x, 3
>  }
> -
> -; CHECK: @test63
> -; CHECK: shl <4 x i32> <i32 1, i32 2, i32 4, i32 8>, %B
> -define <4 x i32> @test63(i32 %n) {
> -entry:
> -  %K = insertelement <4 x i32> undef, i32 %n, i32 0
> -  %B = shufflevector <4 x i32> %K, <4 x i32> undef, <4 x i32> zeroinitializer
> -  %A = add <4 x i32> %B, <i32 0, i32 1, i32 2, i32 3>
> -  %T = shl <4 x i32> <i32 1, i32 1, i32 1, i32 1>, %A
> -  ret <4 x i32> %T
> -}
> -
> -; CHECK: @test64
> -; CHECK: shl i32 524288, %n
> -define i32 @test64(i32 %n) {
> -entry:
> -  %A = add i32 %n, 19
> -  %T = shl i32 1 , %A
> -  ret i32 %T
> -}
>
>
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