[llvm] r260447 - APInt: Simplify EqualSlowCase

[Duncan P. N. Exon Smith via llvm-commits]

> On 2016-Feb-10, at 14:13, Matthias Braun via llvm-commits <llvm-commits at lists.llvm.org> wrote:
> 
> Author: matze
> Date: Wed Feb 10 16:13:10 2016
> New Revision: 260447
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=260447&view=rev
> Log:
> APInt: Simplify EqualSlowCase
> 
> Previously the code used getActiveBits() to determine the highest set
> bit of each APInt first. However doing so requires the same amount of
> memory accesses as simply comparing both numbers right away.
> 
> Removing all the active bit checks leads to simpler code and is faster
> in my benchmark.
> 
> Differential Revision: http://reviews.llvm.org/D16620
> 
> Modified:
>    llvm/trunk/lib/Support/APInt.cpp
> 
> Modified: llvm/trunk/lib/Support/APInt.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Support/APInt.cpp?rev=260447&r1=260446&r2=260447&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Support/APInt.cpp (original)
> +++ llvm/trunk/lib/Support/APInt.cpp Wed Feb 10 16:13:10 2016
> @@ -490,21 +490,8 @@ APInt APInt::operator-(const APInt& RHS)
> }
> 
> bool APInt::EqualSlowCase(const APInt& RHS) const {
> -  // Get some facts about the number of bits used in the two operands.
> -  unsigned n1 = getActiveBits();
> -  unsigned n2 = RHS.getActiveBits();
> -
> -  // If the number of bits isn't the same, they aren't equal
> -  if (n1 != n2)
> -    return false;
> -
> -  // If the number of bits fits in a word, we only need to compare the low word.
> -  if (n1 <= APINT_BITS_PER_WORD)
> -    return pVal[0] == RHS.pVal[0];
> -
> -  // Otherwise, compare everything
> -  for (int i = whichWord(n1 - 1); i >= 0; --i)
> -    if (pVal[i] != RHS.pVal[i])
> +  for (unsigned I = 0, NumWords = getNumWords(); I < NumWords; ++I)
> +    if (pVal[I] != RHS.pVal[I])
>       return false;
>   return true;

I think at this point it seems equivalent to:
```
return std::equal(pVal, pVal + getNumWords(), RHS.pVal);
```


> }
> 
> 
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