[Bug middle-end/84997] Optimize integer operations on floating point constants without -ffast-math

[joseph at codesourcery dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84997

--- Comment #1 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
On Tue, 20 Mar 2018, antoshkka at gmail dot com wrote:

> For example
> 
> int test2(int lhs) {
>     lhs += 2.0;
>     return lhs;
> }

That would need -fno-trapping-math, because if the addition results in a 
double value larger than INT_MAX, under Annex F the conversion back to int 
is defined to raise FE_INVALID along with producing an unspecified value.

> int test2(int lhs) {
>     lhs += 2.000000000000001;
>     return lhs;
> }

That's not correct to optimize unless you generate separate code for lhs 
>= -2 and lhs < -2; conversion from double to int truncates, so test2 (-3) 
== 0.