[llvm-commits] CVS: llvm/lib/Transforms/Scalar/InstructionCombining.cpp

[Chris Lattner]

> Use APInt operators to calculate the carry bits, remove this loop.

Nice :)

-Chris

>
>
> ---
> Diffs of the changes:  (+2 -16)
>
>  InstructionCombining.cpp |   18 ++----------------
>  1 files changed, 2 insertions(+), 16 deletions(-)
>
>
> Index: llvm/lib/Transforms/Scalar/InstructionCombining.cpp
> diff -u llvm/lib/Transforms/Scalar/InstructionCombining.cpp:1.712  
> llvm/lib/Transforms/Scalar/InstructionCombining.cpp:1.713
> --- llvm/lib/Transforms/Scalar/InstructionCombining.cpp:1.712	Fri  
> Mar 30 12:20:39 2007
> +++ llvm/lib/Transforms/Scalar/InstructionCombining.cpp	Fri Mar 30  
> 21:38:39 2007
> @@ -1243,22 +1243,8 @@
>        // To compute this, we first compute the potential carry  
> bits.  These are
>        // the bits which may be modified.  I'm not aware of a  
> better way to do
>        // this scan.
> -      APInt RHSVal(RHS->getValue());
> -
> -      bool CarryIn = false;
> -      APInt CarryBits(BitWidth, 0);
> -      const uint64_t *LHSKnownZeroRawVal = LHSKnownZero.getRawData(),
> -                     *RHSRawVal = RHSVal.getRawData();
> -      for (uint32_t i = 0; i != RHSVal.getNumWords(); ++i) {
> -        uint64_t AddVal = ~LHSKnownZeroRawVal[i] + RHSRawVal[i],
> -                 XorVal = ~LHSKnownZeroRawVal[i] ^ RHSRawVal[i];
> -        uint64_t WordCarryBits = AddVal ^ XorVal + CarryIn;
> -        if (AddVal < RHSRawVal[i])
> -          CarryIn = true;
> -        else
> -          CarryIn = false;
> -        CarryBits.setWordToValue(i, WordCarryBits);
> -      }
> +      const APInt& RHSVal = RHS->getValue();
> +      APInt CarryBits((~LHSKnownZero + RHSVal) ^ (~LHSKnownZero ^  
> RHSVal));
>
>        // Now that we know which bits have carries, compute the  
> known-1/0 sets.
>
>
>
>
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