Re: pragma GCC optimize prevents inlining

[LIU Hao <lh_mouse@126.com>]

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在 2024/1/4 17:01, Hashan Gayasri via Gcc-help 写道:
> I wanted the following to be to be optimized:
> 
> (... ...)
> 
> 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.

Actually `-ffast-math` is an overkill; `-fno-math-errno` isn't practically bad, and can be enabled 
globally:
(https://gcc.godbolt.org/z/hhfP6cYrr)

```
//#pragma GCC push_options
//#pragma GCC optimize ("-ffast-math")

inline int64_t __attribute__ ((const)) RoundToNearestLong (double v)
{
    // assert(fegetround() == FE_TONEAREST);
     return lrint(v);
}

//#pragma GCC pop_options

void
xgset(int64_t& r, double s)
   {
     r = RoundToNearestLong(s);
   }
```

results in
```
xgset(long&, double):
         vcvtsd2si       rax, xmm0
         mov     QWORD PTR [rdi], rax
         ret
```



-- 
Best regards,
LIU Hao


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