[Bug rtl-optimization/71275] New: [7 regression] Performance drop after r235660 on x86-64 in 32-bit mode.

[ysrumyan at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71275

            Bug ID: 71275
           Summary: [7 regression] Performance drop after r235660 on
                    x86-64 in 32-bit mode.
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ysrumyan at gmail dot com
  Target Milestone: ---

Regression can be seen at attached test-case. In the tail block of innermost
loop redundant fill was added:

    before r235660                r235660

.L3:
        addl    $1, %esi          addl    $1, %esi
        addl    %eax, %ebx        addl    %eax, %ebx
        movw    %bp, (%edi,%ecx)  movl    44(%esp), %edx
        movswl  %si, %ebp         movswl  %si, %eax
        cmpl    (%esp), %ebp      cmpl    %edi, %eax
        jl      .L6               movw    %bp, (%edx,%ecx)
                                  jl      .L6

In result we got up to 14% slow-down on one important benchmark.
It is clear that it is not profitable to keep value of loop upper bound on
register instead of the address base.