[Bug target/82418] New: Division on a constant is suboptimal because of not using imul instruction

[antoshkka at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82418

            Bug ID: 82418
           Summary: Division on a constant is suboptimal because of not
                    using imul instruction
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: antoshkka at gmail dot com
  Target Milestone: ---

Following code 

unsigned my_div(unsigned a, unsigned b) {
    return a / 100;
}

Produces assembly:

my_div(unsigned int, unsigned int):
  mov eax, edi
  mov edx, 1374389535
  mul edx
  mov eax, edx
  shr eax, 5
  ret

Clang uses imul instead:

my_div(unsigned int, unsigned int): # @my_div(unsigned int, unsigned int)
  mov eax, edi
  imul rax, rax, 1374389535
  shr rax, 37
  ret