Re: Patch gcc-4.0 should not apply mathematical associative rules for addition or multiplication

[Fariborz Jahanian <fjahanian at apple dot com>]

On Oct 7, 2004, at 8:41 PM, Roger Sayle wrote:

> Hi Fariborz,
>
> Has this issue been filed as a PR in bugzilla yet?  I've just tried
> some tests on mainline and I'm shocked at the unsafe transformations
> being performed by the tree-ssa optimizers.

I will file a PR.

> If you've not already done so, make sure this is targeted at 4.0.0
> with critical priority (a potential show stopper), then to keep RTH
> and Geoff K happy, also file a low priority enhancement request that

I am not sure how. I can check-in my change as the fix for regression 
and then
file a PR for enhancements as you suggested. But RTH considers (X 
*2.0)*2.0
not getting optimized as a regression and not an enhancement. I wait 
for a decision
before filing this other PR.

> (X * 2.0) * 2.0 gets optimized.  The first is a severe regression from
> all previous GCC releases, the latter isn't and possibly may not even
> be suitable for stage3.  If it makes people more comfortable, feel free
> to assign the enhancement request to me.  I wouldn't want either issue
> to get lost.
>
>
> My concern now is how much the performance benefits of the tree-ssa
> merge were exagerated by the fact that we've been performing these
> unsafe mathematical transformations.  Fixing this problem may hurt
> our SPECfp2000 scores   :<

We build SPECs (at least for apple-ppc-darwin with -fast-math).

- Fariborz

> Roger
> --