[Bug rtl-optimization/69633] New: [6 Regression] Redundant move is generated after r228097

[ysrumyan at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69633

            Bug ID: 69633
           Summary: [6 Regression] Redundant move is generated after
                    r228097
           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: ---

Sorry, that we noticed this regression just now but not in September.
After Makarov's fix for 61578 ( and s390 regression) we noticed that for
attached simple test-case extracted from real benchmark one more redundant move
instruction is generated (till 20160202 compiler build):

before fix (postreload dump)
   86: NOTE_INSN_BASIC_BLOCK 4
   40: dx:QI=[si:SI]
   41: ax:QI=[si:SI+0x1]
   42: {si:SI=si:SI+0x3;clobber flags:CC;}
   43: dx:SI=zero_extend(dx:QI)
   44: ax:SI=zero_extend(ax:QI)
   45: cx:SI=zero_extend([si:SI-0x1])
   46: {di:SI=dx:SI*0x4c8b;clobber flags:CC;}
   47: {bx:SI=ax:SI*0x9646;clobber flags:CC;}
   48: {bx:SI=bx:SI+di:SI;clobber flags:CC;}
   49: {di:SI=cx:SI*0x1d2f;clobber flags:CC;}
   50: NOTE_INSN_DELETED
   51: bx:SI=bx:SI+di:SI+0x8000
   52: {bx:SI=bx:SI>>0x10;clobber flags:CC;}
   53: [bp:SI]=bx:QI
   96: bx:SI=dx:SI
   55: {bx:SI=bx:SI<<0xf;clobber flags:CC;}
   57: {bx:SI=bx:SI-dx:SI;clobber flags:CC;}

after fix
   86: NOTE_INSN_BASIC_BLOCK 4
   40: dx:QI=[si:SI]
   41: ax:QI=[si:SI+0x1]
   42: {si:SI=si:SI+0x3;clobber flags:CC;}
   43: dx:SI=zero_extend(dx:QI)
   44: ax:SI=zero_extend(ax:QI)
   45: cx:SI=zero_extend([si:SI-0x1])
   46: {di:SI=dx:SI*0x4c8b;clobber flags:CC;}
   47: {bx:SI=ax:SI*0x9646;clobber flags:CC;}
   48: {bx:SI=bx:SI+di:SI;clobber flags:CC;}
   49: {di:SI=cx:SI*0x1d2f;clobber flags:CC;}
   50: NOTE_INSN_DELETED
   51: bx:SI=bx:SI+di:SI+0x8000
   52: {bx:SI=bx:SI>>0x10;clobber flags:CC;}
   53: [bp:SI]=bx:QI
   96: bx:SI=dx:SI
   55: {bx:SI=bx:SI<<0xf;clobber flags:CC;}
   98: di:SI=bx:SI                           !! redundnat move
   57: {di:SI=di:SI-dx:SI;clobber flags:CC;}

In result, we got >3% slowdown on Silvermont in pie & 32-bit mode.