ISel sinks math library calls below fesetenv

[hiraditya]

#include <fenv.h>
#include <math.h>
__attribute__((const))
long double myrintl(long double x);

long double nearbyintl(long double x) {
  fenv_t e;
  fegetenv(&e);
  long double result = rintl(x);
  fesetenv(&e);
  return result;
}

clang++ -O3

nearbyintl:
        sub     sp, sp, #48
        stp     x29, x30, [sp, #32]
        add     x29, sp, #32
        sub     x0, x29, #8
        str     q0, [sp]
        bl      fegetenv
        sub     x0, x29, #8
        bl      fesetenv
        ldr     q0, [sp]
        ldp     x29, x30, [sp, #32]
        add     sp, sp, #48
        b       rintl // moved here.

https://godbolt.org/z/7h7v1xKee

[llvmbot]

@llvm/issue-subscribers-backend-aarch64

Author: AdityaK (hiraditya)

```c #include <fenv.h> #include <math.h> __attribute__((const)) long double myrintl(long double x);

long double nearbyintl(long double x) {
fenv_t e;
fegetenv(&e);
long double result = rintl(x);
fesetenv(&e);
return result;
}

clang++  -O3

```asm
nearbyintl:
        sub     sp, sp, #<!-- -->48
        stp     x29, x30, [sp, #<!-- -->32]
        add     x29, sp, #<!-- -->32
        sub     x0, x29, #<!-- -->8
        str     q0, [sp]
        bl      fegetenv
        sub     x0, x29, #<!-- -->8
        bl      fesetenv
        ldr     q0, [sp]
        ldp     x29, x30, [sp, #<!-- -->32]
        add     sp, sp, #<!-- -->48
        b       rintl // moved here.

https://godbolt.org/z/7h7v1xKee

[enh-google]

(there's a similar problem with fetestexcept() being moved before the <math.h> function you're trying to test too.)

[topperc]

LLVM requires #pragma STDC FENV_ACCESS ON for this to work.

CC: @andykaylor

[andykaylor]

Yes, @topperc is correct. Per the C standard, access to the floating-point environment is undefined unless the fenv_access state is ON. The default state is implementation defined, but for clang it is OFF by default.

You can enable fenv_access either using the pragma Craig referenced or by compiling with -ffp-model=strict