[llvm-commits] [PATCH] Teach IRBuilder about simplifying BinOp(Value, Constant)

[Török Edwin]

On 2009-01-05 23:01, Eli Friedman wrote:
> On Mon, Jan 5, 2009 at 1:25 AM, Török Edwin <edwintorok at gmail.com> wrote:
>   
>> I added back the Constant* functions in ConstantFolder/TargetFolder,
>> since llvm-gcc is using them (called with constant* params, expecting
>> constant* return).
>>     
>
> +      case Instruction::UDiv:
> +      case Instruction::SDiv:
> +        // udiv/sdiv 0, X -> 0
> +        // This also transforms udiv 0, 0 (undefined behaviour) -> 0.
> +        if (CLHS && CLHS->isZero())
> +          return CLHS;
> +        // udiv/sdiv X, 1 -> X
> +        if (CRHS && CRHS->isOne())
> +          return LHS;
> +        // Don't simplify udiv X, 0 at this point, because it could be used
> +        // to knowingly generate a SIGFPE.
> +        break;
>
> Go ahead and simplify udiv X, 0... we don't make any guarantees about
> what happens when you perform an illegal division, and half-baked
> attempts to preserve that behavior aren't helpful.  If someone really
> wants a SIGFPE, they should use inline asm or something like that.
> Actually, you could just remove the comment, though, since it's not
> likely to show up in normal code.
>   

I'll remove the comment.

Best regards,
--Edwin