[cfe-dev] Why is #pragma STDC FENV_ACCESS not supported?

[Ulrich Weigand via cfe-dev]

Ulrich Weigand/Germany/IBM wrote on 06.03.2018 16:07:34:

> So it appears to me that if we need a chain (or control register
> dependencies etc.), it would be easier on the back-end anyway to
> have a different ISD node, in which case it just might be the easiest
> to pass the STRICT_ nodes through to the back-end if it wants ...
>
> I'll try and go ahead with the SystemZ back-end to see how complicated
> it would actually be to add those nodes, so that we can make an
> informed decision.

I've now implemented the above to handle all the currently supported
STRICT_ FP nodes in the SystemZ back-end (at least for pre-z13 machines,
I'm not supporting vector instructions yet):

https://reviews.llvm.org/D45576

I've tested this using a hacked clang front-end that always uses
constrained intrisincs in place of most regular FP operations,
and it at least still passes the LNT test-suite.

I'd appreciate any comments on whether this looks like an acceptable
approach.  In particular, I'd like to hear from Andrew how this
compares with your approach -- I understand you have some other
method in mind to handle this for x86?

Bye,
Ulrich
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