[Bug middle-end/59470] [4.8 Regression] libstdc++ miscompilation after r205709

[vmakarov at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59470

--- Comment #12 from Vladimir Makarov <vmakarov at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #9)
>  In -fdump-rtl-reload-slim we have incorrect:
> 
>    92: {sp:SI=sp:SI-0x30;clobber flags:CC;}
>    94: {dx:SI=sp:SI+0x2f;clobber flags:CC;}
>    95: NOTE_INSN_DELETED
>    96: {dx:SI=dx:SI&0xfffffffffffffff0;clobber flags:CC;}
> ...
>   441: [bp:SI-0x2c]=dx:SI
>       REG_DEAD dx:SI
> ...
>   442: dx:SI=[bp:SI-0x2c]
>   152: {dx:SI=dx:SI-cx:SI;clobber flags:CC;}
>       REG_DEAD dx:SI
>   153: ax:SI=dx:SI+0x14
>       REG_DEAD dx:SI
>   461: [bp:SI-0x2c]=ax:SI
>       REG_DEAD ax:SI
> ...
>   164: {sp:SI=sp:SI-ax:SI;clobber flags:CC;}
>       REG_DEAD ax:SI
>   166: {ax:SI=sp:SI+0x2f;clobber flags:CC;}
>   167: NOTE_INSN_DELETED
>   168: {ax:SI=ax:SI&0xfffffffffffffff0;clobber flags:CC;}
>   170: {ax:SI=ax:SI+0x2;clobber flags:CC;}
>       REG_DEAD ax:SI
>   423: dx:SI=ax:SI
>       REG_DEAD ax:SI
> ...
>   174: [sp:SI+0x1c]=cx:SI
>       REG_DEAD cx:SI
>       REG_EQUAL frame:SI-0x8
>   460: dx:SI=[bp:SI-0x2c]
>   175: [sp:SI+0x18]=dx:SI
>       REG_DEAD dx:SI
>   444: [bp:SI-0x2c]=dx:SI
>   425: dx:SI=dx:SI
>       REG_DEAD dx:SI
>   176: [sp:SI+0x14]=dx:SI
>       REG_DEAD dx:SI
>   177: [sp:SI+0x10]=si:SI
>   178: dx:SI=sign_extend([di:SI+0x25])
>       REG_EQUIV [sp:SI+0xc]
>   179: [sp:SI+0xc]=dx:SI
>       REG_DEAD dx:SI
>   180: [sp:SI+0x8]=ax:SI
>       REG_DEAD ax:SI
>   426: cx:SI=[bp:SI-0x54]
>   181: [sp:SI+0x4]=cx:SI
>       REG_DEAD cx:SI
>   427: cx:SI=[bp:SI-0x48]
>   182: [sp:SI]=cx:SI
>       REG_DEAD cx:SI
>   183: call
> [`_ZNKSt7num_putIcSt19ostreambuf_iteratorIcSt11char_traitsIcEEE12_M_group_int
> EPKcjcRSt8ios_basePcS9_Ri'] argc:0x20
> 
> The bug I see is in the 460/444 reloads for insn 175.  The correct value
> that insn 176 is supposed to store is live in edx register iup to insn 174,
> but LRA? decides to throw away it's value when reloading insn 175 and loads
> there the value of former pseudo r59 from [bp-0x2c], stores that correctly
> into [sp+0x18] and saves to [bp-0x2c] again (why?  the value hasn't really
> changed).  But the old edx (pseudo r82) is lost.  Vlad, can you please have
> a look?

 The generated code is wrong.  The added patch fixes it but it does not fix
libstdc++11 regressions.  The path results in the following code generation: 

  170: {ax:SI=ax:SI+0x2;clobber flags:CC;}
      REG_DEAD ax:SI
  423: dx:SI=ax:SI
      REG_DEAD ax:SI
  446: NOTE_INSN_DELETED
  171: ax:SI=[di:SI+0xc]
  172: cx:SI=[di:SI+0x8]
  424: [bp:SI-0x54]=cx:SI
      REG_DEAD cx:SI
  470: NOTE_INSN_DELETED
  445: NOTE_INSN_DELETED
  173: {cx:SI=bp:SI-0x20;clobber flags:CC;}
      REG_EQUIV frame:SI-0x8
  174: [sp:SI+0x1c]=cx:SI
      REG_DEAD cx:SI
      REG_EQUAL frame:SI-0x8
  460: cx:SI=[bp:SI-0x2c]
  175: [sp:SI+0x18]=cx:SI
      REG_DEAD cx:SI
  444: [bp:SI-0x2c]=dx:SI
  425: dx:SI=dx:SI
      REG_DEAD dx:SI
  176: [sp:SI+0x14]=dx:SI
      REG_DEAD dx:SI
  177: [sp:SI+0x10]=si:SI
  178: dx:SI=sign_extend([di:SI+0x25])
      REG_EQUIV [sp:SI+0xc]
  179: [sp:SI+0xc]=dx:SI
      REG_DEAD dx:SI
  180: [sp:SI+0x8]=ax:SI
      REG_DEAD ax:SI
  426: cx:SI=[bp:SI-0x54]
  181: [sp:SI+0x4]=cx:SI
      REG_DEAD cx:SI
  427: cx:SI=[bp:SI-0x48]
  182: [sp:SI]=cx:SI
      REG_DEAD cx:SI
  183: call
[`_ZNKSt7num_putIcSt19ostreambuf_iteratorIcSt11char_traitsIcEEE12_M_group_intEPKcjcRSt8ios_basePcS9_Ri']
argc:0x20
  184: cx:SI=[bp:SI-0x20]