[Bug rtl-optimization/71768] New: Missed trivial rematerialiation oppurtunity

["hubicka at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71768

            Bug ID: 71768
           Summary: Missed trivial rematerialiation oppurtunity
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hubicka at gcc dot gnu.org
  Target Milestone: ---

Compiling
#define vector __attribute__ ((vector_size (16)))
const vector int cst={10,10,10,10};
int t()
{
  vector int val = cst;
  asm("#%0"::"x"(val));
  e();
  asm("#%0"::"x"(val));
}
Results in:
t:
.LFB0:
        .cfi_startproc
        subq    $24, %rsp
        .cfi_def_cfa_offset 32
        vmovaps .LC0(%rip), %xmm0
#APP
# 6 "t.c" 1
        #%xmm0
# 0 "" 2
#NO_APP
        xorl    %eax, %eax
        vmovaps %xmm0, (%rsp)
        call    e
        vmovaps (%rsp), %xmm0
#APP
# 8 "t.c" 1
        #%xmm0
# 0 "" 2
#NO_APP
        addq    $24, %rsp
        .cfi_def_cfa_offset 8
        ret

Which is clearly suboptimal, because xmm0 can be rematerialized again from LC0.
This hits pretty badly the exchange2 benchmark with -O3 -march=bdver2 where the
function is self recursive and we end up having many constants cached in XMM
registers.