[cfe-commits] r59105 - /cfe/trunk/lib/AST/ExprConstant.cpp

[Fariborz Jahanian]

On Nov 11, 2008, at 11:04 PM, Chris Lattner wrote:

> Author: lattner
> Date: Wed Nov 12 01:04:29 2008
> New Revision: 59105
>
> URL: http://llvm.org/viewvc/llvm-project?rev=59105&view=rev
> Log:
> Teach the aggressive constant folder to fold X && 0 -> 0 and X || 1 - 
> > 1

I assume that you care that 'X' has no side-effect here.

- fariborz

>
>
> Modified:
>    cfe/trunk/lib/AST/ExprConstant.cpp
>
> Modified: cfe/trunk/lib/AST/ExprConstant.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/ExprConstant.cpp?rev=59105&r1=59104&r2=59105&view=diff
>
> = 
> = 
> = 
> = 
> = 
> = 
> = 
> = 
> ======================================================================
> --- cfe/trunk/lib/AST/ExprConstant.cpp (original)
> +++ cfe/trunk/lib/AST/ExprConstant.cpp Wed Nov 12 01:04:29 2008
> @@ -323,8 +323,28 @@
> bool IntExprEvaluator::VisitBinaryOperator(const BinaryOperator *E) {
>   // The LHS of a constant expr is always evaluated and needed.
>   llvm::APSInt RHS(32);
> -  if (!Visit(E->getLHS()))
> +  if (!Visit(E->getLHS())) {
> +    // If the LHS is unfoldable, we generally can't fold this.   
> However, if this
> +    // is a logical operator like &&/||, and if we know that the  
> RHS determines
> +    // the outcome of the result (e.g. X && 0), return the outcome.
> +    if (!E->isLogicalOp())
> +      return false;
> +
> +    // If this is a logical op, see if the RHS determines the  
> outcome.
> +    EvalInfo Info2(Info.Ctx);
> +    if (!EvaluateInteger(E->getRHS(), RHS, Info2))
> +      return false;
> +
> +    // X && 0 -> 0, X || 1 -> 1.
> +    if (E->getOpcode() == BinaryOperator::LAnd && RHS == 0 ||
> +        E->getOpcode() == BinaryOperator::LOr  && RHS != 0) {
> +      Result = RHS != 0;
> +      Result.zextOrTrunc(getIntTypeSizeInBits(E->getType()));
> +      return true;
> +    }
> +
>     return false; // error in subexpression.
> +  }
>
>   bool OldEval = Info.isEvaluated;
>
>
>
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