[Bug target/82883] New: eax register unnecessary consumed

[antoshkka at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82883

            Bug ID: 82883
           Summary: eax register unnecessary consumed
           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 example:

void foo(char* ch) {
    __builtin_memcpy(ch, "Hello word", 6);
}


Produces the assembly

foo(char*):
        mov     eax, 8303   <=== This is not required
        mov     DWORD PTR [rdi], 1819043144
        mov     WORD PTR [rdi+4], ax
        ret

The code could be further optimized to not use the eax register. For example
clang does the following:

foo(char*):                               # @foo(char*)
        mov     word ptr [rdi + 4], 8303
        mov     dword ptr [rdi], 1819043144
        ret