llvm dev - Apr 2012 - [LLVMdev] Representing -ffast-math at the IR level

Hi Duncan,

I like the changes to IRBuilder and how the operator can't change it.
Looks a lot safer (mistake-wise) and more convenient.

This function won't to remove a previously set tag, which could be
used by optimisations or inlining.

+  Instruction *AddFPMathTag(Instruction *I, MDNode *FPMathTag) const {
+    if (!FPMathTag)
+      FPMathTag = DefaultFPMathTag;
+    if (FPMathTag)
+      I->setMetadata(LLVMContext::MD_fpmath, FPMathTag);
+    return I;
+  }

If you want to keep it as only Add, then make FPMathTag = 0 so that
you can easily add the default by just calling AddFPMathTag(instr);

But I'd add a ClearFPMathTag function for optimisations/inlining. Maybe
later.

Also, would be good to make sure the instruction is, in fact, a
floating point operation. Either via restricting the type or asserting
on it.

-- 
cheers,
--renato

http://systemcall.org/

Hi Renato,
> I like the changes to IRBuilder and how the operator can't change it.
> Looks a lot safer (mistake-wise) and more convenient.
thanks!
> This function won't to remove a previously set tag, which could be
> used by optimisations or inlining.
This is private to IRBuilder and is only applied to newly created instructions,
thus removing tags is not useful.  I guess it could be exposed for general use -
is that what you are suggesting?  If so, I think it would be better if MDBuilder
got methods for applying metadata such as:
   SetTBAAMetadata(Instruction *I, MDNode *MD);
   SetFPMathMetadata(Instruction *I, MDNode *MD);
along with getters.  I will add that.
>
> +  Instruction *AddFPMathTag(Instruction *I, MDNode *FPMathTag) const {
> +    if (!FPMathTag)
> +      FPMathTag = DefaultFPMathTag;
> +    if (FPMathTag)
> +      I->setMetadata(LLVMContext::MD_fpmath, FPMathTag);
> +    return I;
> +  }
>
> If you want to keep it as only Add, then make FPMathTag = 0 so that
> you can easily add the default by just calling AddFPMathTag(instr);
>
> But I'd add a ClearFPMathTag function for optimisations/inlining. Maybe
later.
See above.
> Also, would be good to make sure the instruction is, in fact, a
> floating point operation. Either via restricting the type or asserting
> on it.
That would be appropriate for MDBuilder - I will do it.

CIao, Duncan.

Btw, the assert in MDNode *CreateFPMath(float Accuracy) is
unnecessary. Trichotomy guarantees it will be right. ;)

-- 
cheers,
--renato

http://systemcall.org/

Hi Renato,
> Btw, the assert in MDNode *CreateFPMath(float Accuracy) is
> unnecessary. Trichotomy guarantees it will be right. ;)
what if Accuracy is NaN?

Ciao, Duncan.