On 04/01/2024 10:01, Hashan Gayasri via Gcc-help wrote:
Hi,
I noticed that GCC doesn't inline functions that have extra optimization
options added via pragma GCC optimize after the pop_options statement.
If the optimizations are different between the caller and the callee, seems
like gcc behaves as if the called function's definition is opaque and not
visible at all (as if it was declared in a different translation unit). It
doesn't even notice that the function doesn't have side effects unless
marked so explicitly.
I wanted the following to be to be optimized:
#pragma GCC push_options
#pragma GCC optimize ("-ffast-math")
inline int64_t __attribute__ ((const)) RoundToNearestLong (double v)
{
assert(fegetround() == FE_TONEAREST);
return std::lrint(v);
}
#pragma GCC pop_options
So that std::lrint uses the vcvtsd2si instruction on X86 with SSE2. It
does that but prevents the instruction from being inlined. I complied with
- O3 -march=native -DNDEBUG.
If I used attribute always_inline, the inlined version didn't seem to
respect the additional optimization options I provided.
const and pure function attributes helped in removing unused/no side effect
code paths but the function still got called.
Please advice if there's any way work around for this. Using intrinsics
works but less than ideal.
(Also let me know if I should be sending this to a different mailing list)
Thanks in advance!
Best Regards,
Hashan Gayasri
This is a general limitation in GCC, as far as I know. I have come
across it myself (in my case it was the "-fwrapv" flag). As far as I
remember from a previous discussion long ago, there is no easy workaround.
