https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96862
--- Comment #5 from Marc Glisse <glisse at gcc dot gnu.org> --- "[Note: This document does not require an implementation to support the FENV_ACCESS pragma; it is implementation-defined (15.8) whether the pragma is supported. As a consequence, it is implementation-defined whether these functions can be used to test floating-point status flags, set floating-point control modes, or run under non-default mode settings. If the pragma is used to enable control over the floating-point environment, this document does not specify the effect on floating-point evaluation in constant expressions. — end note]" So the C++ standard lets us choose what we want gcc to do in this case. The C standard is of course more precise, but using its own definition of constant expressions http://port70.net/~nsz/c/c11/n1570.html#F.8.4 "1 An arithmetic constant expression of floating type, other than one in an initializer for an object that has static or thread storage duration, is evaluated (as if) during execution; thus, it is affected by any operative floating-point control modes and raises floating-point exceptions as required by IEC 60559 (provided the state for the FENV_ACCESS pragma is ''on'').366) 2 EXAMPLE #include <fenv.h> #pragma STDC FENV_ACCESS ON void f(void) { float w[] = { 0.0/0.0 }; // raises an exception static float x = 0.0/0.0; // does not raise an exception float y = 0.0/0.0; // raises an exception double z = 0.0/0.0; // raises an exception /* ... */ } 3 For the static initialization, the division is done at translation time, raising no (execution-time) floating- point exceptions. On the other hand, for the three automatic initializations the invalid division occurs at execution time." So Jakub's proposition makes sense, fold inexact operations when we have to (and use default (nearest) rounding in that case, as long as we don't have pragma fenv_round). Initializing a global (before main starts) also looks like a place where folding could make sense, although it is less important.
