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From: "vmakarov at redhat dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug rtl-optimization/57131] [4.8/4.9 Regression] Wrong register assignment?
Date: Thu, 02 May 2013 03:03:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57131

Vladimir Makarov <vmakarov at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |vmakarov at redhat dot com

--- Comment #3 from Vladimir Makarov <vmakarov at redhat dot com> 2013-05-02 03:03:34 UTC ---
(In reply to comment #2)
> Apparently went away with the http://gcc.gnu.org/r198432 fix, but it isn't
> clear whether that change was meant to fix this or just made the bug latent.
> Anyway, still reproduceable on the 4.8 branch.
> What I'm seeing before that change is that extendsidi2_1 pattern with MEM
> destination LRA chooses %ebx as (clobber (scratch:SI)) register, eventhough
> %ebx
> is live across that instruction (there is
> (insn 14 74 68 2 (set (reg:SI 3 bx [orig:83 D.1395 ] [83])
>         (mem/v/c:SI (plus:SI (reg/f:SI 7 sp)
>                 (const_int 72 [0x48])) [0 x4+0 S4 A64])) pr57131.c:11 85
> {*movsi_internal}
>      (nil))
> (insn 68 14 73 2 (set (reg:SI 3 bx [orig:83 D.1395 ] [83])
>         (reg:SI 3 bx [orig:83 D.1395 ] [83])) pr57131.c:11 85 {*movsi_internal}
>      (expr_list:REG_DEAD (reg:SI 3 bx [orig:83 D.1395 ] [83])
>         (nil)))
> some insns before it and:
> (insn 65 24 26 2 (set (reg:SI 5 di [orig:83 D.1395 ] [83])
>         (reg:SI 3 bx [orig:83 D.1395 ] [83])) pr57131.c:11 85 {*movsi_internal}
>      (expr_list:REG_DEAD (reg:SI 3 bx [orig:83 D.1395 ] [83])
>         (nil)))
> some insns after it.  Not sure if the noop move with REG_DEAD has anything to
> do with that.  Vlad, can you please have a look?

http://gcc.gnu.org/r198432 was a right solution for this bug.  LRA don't pay
attention to NO_REGS pseudos during assignment although ebx was assigned to
NO_REGS r95 (which is reflected in reg_renumber).

At some points of LRA work reg notes can be invalid.  LRA makes them up to date
after live subpass (lra-lives.c).  It needs only correct live info on bb
borders.

So I'd close this PR.