[Bug rtl-optimization/82578] New: Redundant instructions emitted starting with r204212

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82578

            Bug ID: 82578
           Summary: Redundant instructions emitted starting with r204212
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: krebbel at gcc dot gnu.org
  Target Milestone: ---

Starting with r204212 (2013-10-30) a redundant thread pointer extract is
emitted.

static __thread int counter;

void gs_handler(void)
{
  counter++;
}

compiled with: -O2 -S

2xear with r204211:

gs_handler:
        larl    %r5,.L2
        ear     %r1,%a0
        sllg    %r1,%r1,32
        ear     %r1,%a1
        lg      %r2,.L3-.L2(%r5)
        l       %r3,0(%r1,%r2)
        ahi     %r3,1
        st      %r3,0(%r1,%r2)
        br      %r14


4xear with r204212:

gs_handler:
        larl    %r5,.L2
        ear     %r2,%a0
        sllg    %r2,%r2,32
        ear     %r1,%a0
        ear     %r2,%a1
        sllg    %r1,%r1,32
        lg      %r3,.L3-.L2(%r5)
        ear     %r1,%a1
        l       %r2,0(%r2,%r3)
        ahi     %r2,1
        st      %r2,0(%r1,%r3)
        br      %r14