[Bug middle-end/114270] New: Integer multiplication on floating point constant with conversion back to integer is not optimized

[antoshkka at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114270

            Bug ID: 114270
           Summary: Integer multiplication on floating point constant with
                    conversion back to integer is not optimized
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: antoshkka at gmail dot com
  Target Milestone: ---

Consider the following example:

unsigned test(unsigned x) {
    return (unsigned)(x * 0.5);
}

With -O2 GCC generates the code with a fair conversion to fp and
multiplication:

test(unsigned int):
  mov edi, edi
  pxor xmm0, xmm0
  cvtsi2sd xmm0, rdi
  mulsd xmm0, QWORD PTR .LC0[rip]
  cvttsd2si rax, xmm0
  ret

However the multiplication does not overflow and the floating point constant is
a normal number.

A more optimal code should look like the following:

test(unsigned int):
  mov eax, edi
  shr eax
  ret

Probably the optimization could be used for
* any multiplication of integer on positive fp-number less or equal to 1.0
* any division of integer on positive fp-number greater or equal to 1.0
if the result is converted back to integer