[Bug rtl-optimization/67145] New: [6 Regression] Innefective plus-minus simplification

[afomin.mailbox at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67145

            Bug ID: 67145
           Summary: [6 Regression] Innefective plus-minus simplification
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: afomin.mailbox at gmail dot com
                CC: izamyatin at gmail dot com
  Target Milestone: ---
            Target: i686

Created attachment 36145
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=36145&action=edit
Reproducer

For the loop in the attached test compiled with -O3 -m32 -fPIE -pie after
r224768 we generate 20 insns because of additional copies (first seen at fwprop
pass)
mov    (%esp),%edi
mov    (%edi),%edx
mov    0x4(%esp),%edi
add    %esi,%edx
movzbl (%edx,%ebx,1),%edx
mov    %dl,(%ecx,%eax,1)
mov    (%edi),%edx
mov    0x8(%esp),%edi
add    %ebp,%edx
add    (%edi),%edx
mov    0xc(%esp),%edi
movzbl (%edx),%edx
mov    %dl,0x1(%ecx,%eax,1)
mov    %esi,%edx
add    (%edi),%edx
movzbl (%edx,%ebx,1),%edx
mov    %dl,0x2(%ecx,%eax,1)
add    $0x3,%eax
cmp    $0xfffffffd,%eax
jne    50 <foo+0x50>

while for r224767 we generate just 18 insns
mov    0x0(%ebp),%edx
mov    0x4(%esp),%esi
add    %ecx,%edx
movzbl (%edx),%edx
mov    %dl,(%ebx,%eax,1)
mov    %ecx,%edx
add    (%esi),%edx
add    (%edi),%edx
mov    (%esp),%esi
movzbl (%edx),%edx
mov    %dl,0x1(%ebx,%eax,1)
mov    (%esi),%edx
add    %ecx,%edx
movzbl (%edx),%edx
mov    %dl,0x2(%ebx,%eax,1)
add    $0x3,%eax
cmp    $0xfffffffd,%eax
jne    48 <foo+0x48>

Probably this simplification should be tuned for array indices.