[Bug rtl-optimization/69052] New: [6 Regression] Performance regression after r229402.

["ysrumyan at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69052

            Bug ID: 69052
           Summary: [6 Regression] Performance regression after r229402.
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ysrumyan at gmail dot com
  Target Milestone: ---

In loop_invariant phase additional function inv_can_prop_to_addr_use which
tried to determine if forward propagation for cheap address is possible through
call of verify_changes which is very poor in comparison with combine phase.
For example, for attached test-case it tries
(gdb) call debug_rtx(def_insn)
(insn 69 67 70 9 (set (reg/f:SI 149)
        (plus:SI (reg:SI 87)
            (const:SI (unspec:SI [
                        (symbol_ref:SI ("ind") [flags 0x2] <var_decl
0x7ffff7ffbe10 ind>)
                    ] UNSPEC_GOTOFF)))) t1.c:40 212 {*leasi}
     (expr_list:REG_DEAD (reg:SI 87)
        (nil)))
(gdb) call debug_rtx(use_insn)
(insn 70 69 71 9 (set (reg:SI 150)
        (mem/u:SI (plus:SI (mult:SI (reg/v:SI 90 [ k ])
                    (const_int 4 [0x4]))
                (reg/f:SI 149)) [1 ind S4 A32])) t1.c:40 86 {*movsi_internal}
     (expr_list:REG_DEAD (reg/f:SI 149)
        (nil)))
and determines that propagation is not possible:
(gdb) p ok
$1 = false
but combine can do such substitution.

This leads to undesired code motion and performance lost:
for stmt out[ind[k]] = result
before r229402
        movl    ind@GOTOFF(%ebx,%esi,4), %eax
        movl    12(%esp), %edi
        movl    %ebp, (%edi,%eax,4)
after r229402
        movl    28(%esp), %eax
        movl    24(%esp), %ebx
        movl    (%eax,%esi,4), %eax
        movl    %edi, (%ebx,%eax,4)

redundant fill has been generated by LRA.

Since emulation combine phase is not so simple I assume that additional hook
should be added to turn off such transformation for x86 in PIE mode.