[PATCH] propagate IR-level fast-math-flags to DAG nodes, disabled by default

[Sanjay Patel]

Does anyone see a workaround to do this piecemeal with FMF enabled?

Otherwise, I see about 30 checks for UnsafeFPMath transforms in
DAGCombiner...so I could revert r243687, start working on the combiner
fixes, and then turn the flag back on when DAGCombiner is FMF-clean.

But this wouldn't be perfect if you have more UnsafeFPMath transforms in
your backend. You'd have to patch those too before we turn the flag back on.

Any other ideas about how to proceed?

On Mon, Aug 3, 2015 at 4:52 PM, escha <escha at apple.com> wrote:

> We’re getting significant CSE regressions on our backend, caused by the
> fact that none of the DAG folds propagate fast-math flags. This results in
> nodes not being CSE’d, since we only CSE nodes if they have identical flags
> (and thus worse codegen).
>
> I was able to get rid of many of them by adding flag propagation to FNEG
> folding, but there’s way more than just that.
>
> —escha
>
> On Jul 29, 2015, at 11:51 AM, Sanjay Patel <spatel at rotateright.com> wrote:
>
> For reference, fixes for PR24141 are in:
>
> http://reviews.llvm.org/rL243293 <https://urldefense.proofpoint.com/v2/url?u=http-3A__reviews.llvm.org_rL243293&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=mQ4LZ2PUj9hpadE3cDHZnIdEwhEBrbAstXeMaFoB9tg&m=EH36SVVrOANvPpWUfmtjHvcZene16JZYtYcOsOWHmmQ&s=oJkUxyP-U28dL9zPjcyCjESFgqf9fEa1WxScYHC1BLE&e=>http://reviews.llvm.org/rL243498 <https://urldefense.proofpoint.com/v2/url?u=http-3A__reviews.llvm.org_rL243498&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=mQ4LZ2PUj9hpadE3cDHZnIdEwhEBrbAstXeMaFoB9tg&m=EH36SVVrOANvPpWUfmtjHvcZene16JZYtYcOsOWHmmQ&s=9UShb3DxctMQors5uP4ErkfZ2ETsaqYXEeRLX8qKYt0&e=>http://reviews.llvm.org/rL243500 <https://urldefense.proofpoint.com/v2/url?u=http-3A__reviews.llvm.org_rL243500&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=mQ4LZ2PUj9hpadE3cDHZnIdEwhEBrbAstXeMaFoB9tg&m=EH36SVVrOANvPpWUfmtjHvcZene16JZYtYcOsOWHmmQ&s=S5dEJW-NYcq9yLglX74iN2esNypm3qfP6wCNidxysx8&e=>
>
> ...assuming those don't cause new breakage, it's finally, really time to
> flip the FMF flag...and wait for more breakage.
>
> On Mon, Jul 20, 2015 at 11:34 AM, Sanjay Patel <spatel at rotateright.com>
> wrote:
>
>>
>>
>> On Fri, Jul 17, 2015 at 4:42 PM, Nick Lewycky <nlewycky at google.com>
>> wrote:
>>
>>> On 9 July 2015 at 15:27, Sanjay Patel <spatel at rotateright.com> wrote:
>>>
>>>> Hi Nick,
>>>>
>>>> The reciprocal fix is in at r241826. Please let me know when you find
>>>> another failure. Thanks!
>>>>
>>>
>>> Thank you! I tested it and found exactly nothing wrong. Hopefully I
>>> didn't goof the testing, but I think it's time to flip the flag to true,
>>> then wait a few days before removing the flag entirely.
>>>
>>
>> Wow...I'm surprised, but I'll hope for the best. Thanks for the testing!
>>
>>
>> Note however, that we still have problems with PR24141 which is related
>>> to unsafe fp math, but doesn't change with the -enable-fmf-dag flag.
>>>
>>
>> Proposed fix:
>> http://reviews.llvm.org/D11345
>> <https://urldefense.proofpoint.com/v2/url?u=http-3A__reviews.llvm.org_D11345&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=mQ4LZ2PUj9hpadE3cDHZnIdEwhEBrbAstXeMaFoB9tg&m=EH36SVVrOANvPpWUfmtjHvcZene16JZYtYcOsOWHmmQ&s=q0g5ELtAiUzID-3xj21ZzkiASkbrFaYCWXDy-nBF0OI&e=>
>>
>>
>>
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