[Bug target/78967] New: inserts are not effective

[ubizjak at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78967

            Bug ID: 78967
           Summary: inserts are not effective
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ubizjak at gmail dot com
  Target Milestone: ---

Similar to PR78904, following testcase:

--cut here--
struct S1
{
  unsigned char pad1;
  unsigned char val;
  unsigned short pad2;
};

extern unsigned char t;

struct S1 foo (struct S1 a)
{
  a.val = t;

  return a;
}
--cut here--

compiles to (-O2):

        movzbl  t(%rip), %edx
        movl    %edi, %eax
        movb    %dl, %ah

Optimal code would be:

        movl    %edi, %eax
        movb    t(%rip), %ah