[llvm-commits] [llvm] r53812 - /llvm/trunk/lib/Analysis/ScalarEvolution.cpp

[Chris Lattner]

On Jul 20, 2008, at 7:51 PM, Nick Lewycky wrote:

> Author: nicholas
> Date: Sun Jul 20 21:51:31 2008
> New Revision: 53812
>
> URL: http://llvm.org/viewvc/llvm-project?rev=53812&view=rev
> Log:
> Switch on the use of arbitrary precision integers in scalar  
> evolution. This will
> bail after 256-bits to avoid producing code that the backends can't  
> handle.
> Previously, we capped it at 64-bits, preferring to miscompile in  
> those cases.
>
> This change also reverts much of r52248 because the invariants the  
> code was
> expecting are now being met.

Uh, legalizetypes is not enabled by default.  Please revert this.  Did  
this pass make check?  If so, we need better tests.

-Chris

>
>
> Modified:
>    llvm/trunk/lib/Analysis/ScalarEvolution.cpp
>
> Modified: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolution.cpp?rev=53812&r1=53811&r2=53812&view=diff
>
> = 
> = 
> = 
> = 
> = 
> = 
> = 
> = 
> ======================================================================
> --- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
> +++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Sun Jul 20 21:51:31  
> 2008
> @@ -538,20 +538,12 @@
>
>   assert(K < 9 && "We cannot handle such long AddRecs yet.");
>
> -  // FIXME: A temporary hack to remove in future.  Arbitrary  
> precision integers
> -  // aren't supported by the code generator yet.  For the dividend,  
> the bitwidth
> -  // we use is the smallest power of 2 greater or equal to K*W and  
> less or equal
> -  // to 64.  Note that setting the upper bound for bitwidth may  
> still lead to
> -  // miscompilation in some cases.
> -  unsigned DividendBits = 1U << Log2_32_Ceil(K * It->getBitWidth());
> -  if (DividendBits > 64)
> -    DividendBits = 64;
> -#if 0 // Waiting for the APInt support in the code generator...
>   unsigned DividendBits = K * It->getBitWidth();
> -#endif
> +  if (DividendBits > 256)
> +    return new SCEVCouldNotCompute();
>
>   const IntegerType *DividendTy = IntegerType::get(DividendBits);
> -  const SCEVHandle ExIt = SE.getTruncateOrZeroExtend(It, DividendTy);
> +  const SCEVHandle ExIt = SE.getZeroExtendExpr(It, DividendTy);
>
>   // The final number of bits we need to perform the division is the  
> maximum of
>   // dividend and divisor bitwidths.
> @@ -573,12 +565,7 @@
>       Dividend *= N-(K-1);
>     if (DividendTy != DivisionTy)
>       Dividend = Dividend.zext(DivisionTy->getBitWidth());
> -
> -    APInt Result = Dividend.udiv(Divisor);
> -    if (Result.getBitWidth() != It->getBitWidth())
> -      Result = Result.trunc(It->getBitWidth());
> -
> -    return SE.getConstant(Result);
> +    return SE.getConstant(Dividend.udiv(Divisor).trunc(It- 
> >getBitWidth()));
>   }
>
>   SCEVHandle Dividend = ExIt;
> @@ -587,11 +574,10 @@
>       SE.getMulExpr(Dividend,
>                     SE.getMinusSCEV(ExIt, SE.getIntegerSCEV(i,  
> DividendTy)));
>
> -  return SE.getTruncateOrZeroExtend(
> -             SE.getUDivExpr(
> -                 SE.getTruncateOrZeroExtend(Dividend, DivisionTy),
> -                 SE.getConstant(Divisor)
> -             ), It->getType());
> +  if (DividendTy != DivisionTy)
> +    Dividend = SE.getZeroExtendExpr(Dividend, DivisionTy);
> +  return SE.getTruncateExpr(SE.getUDivExpr(Dividend,  
> SE.getConstant(Divisor)),
> +                            It->getType());
> }
>
> /// evaluateAtIteration - Return the value of this chain of  
> recurrences at
>
>
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