Block optimize pragma on EDG

[ilazaric]

EDG over GCC likes to pretend to be GCC in a lot of macros, but not all.
It does not define __OPTIMIZE__ ever.
So we would erroneously emit pragma optimize Og even in optimized builds.

[vitaut]

Is emitting a pragma actually harmful on EDG? Could you elaborate what exactly happens in the optimized mode?

[ilazaric]

Not from EDG perspective, but yes from GCC perspective.
EDG consumes C++ and generates C code, which is compiled with GCC.
The pragma optimize is just passed through, so if you were wanting a O2 build,
you're instead getting a Og build, pretty bad in most contexts.

But until recently there was an even worse situation.
When GCC -O2 would hit the pragma optimize,
it wouldn't really switch all options to what Og does,
the relevant part is it would become -Og -fipa-icf-functions build.
And EDG would emit certain kind of C code that runs into a GCC bug:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127703

But it seems something changed in EDG since then,
couldn't get trunk to reproduce running into this bug,
and all you run into is unexpected horrible performance :)

[ilazaric]

Example on EDG 7: https://godbolt.org/z/jh5zhT3Kh

[vitaut]

Merged, thanks!