[llvm-commits] [llvm] r52003 - /llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp

[Chris Lattner]

On Jun 5, 2008, at 7:23 AM, Zhou Sheng wrote:

> Author: sheng
> Date: Thu Jun  5 09:23:44 2008
> New Revision: 52003
>
> URL: http://llvm.org/viewvc/llvm-project?rev=52003&view=rev
> Log:
> If BitWidth equals to ShtAmt, the RHSKnownZero[BitWidth-ShiftAmt-1]  
> will
> crash the opt. Just fix this.

Hi Sheng,

What happens if ShiftAmt is larger?  Shifting by the bitwidth or more  
is undefined... maybe this should be caught earlier?

-Chris

>
>
> Test case in llvm/test/Transforms/InstCombine/2008-06-05-ashr-crash.ll
>
> Modified:
>    llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp
>
> Modified: llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp?rev=52003&r1=52002&r2=52003&view=diff
>
> = 
> = 
> = 
> = 
> = 
> = 
> = 
> = 
> ======================================================================
> --- llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp  
> (original)
> +++ llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp Thu  
> Jun  5 09:23:44 2008
> @@ -1236,7 +1236,7 @@
>
>       // If the input sign bit is known to be zero, or if none of  
> the top bits
>       // are demanded, turn this into an unsigned shift right.
> -      if (RHSKnownZero[BitWidth-ShiftAmt-1] ||
> +      if (BitWidth == ShiftAmt || RHSKnownZero[BitWidth-ShiftAmt-1]  
> ||
>           (HighBits & ~DemandedMask) == HighBits) {
>         // Perform the logical shift right.
>         Value *NewVal = BinaryOperator::CreateLShr(
>
>
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