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Re: 6 GCC regressions, 2 new, with your patch on 2002-07-20T23:26:42Z.
- From: Richard Henderson <rth at redhat dot com>
- To: Jan Hubicka <jh at suse dot cz>
- Cc: Roger Sayle <roger at eyesopen dot com>, gcc-patches at gcc dot gnu dot org, gcc-regression at gcc dot gnu dot org
- Date: Wed, 24 Jul 2002 16:40:42 -0700
- Subject: Re: 6 GCC regressions, 2 new, with your patch on 2002-07-20T23:26:42Z.
- References: <200207210301.g6L31ih19173@maat.sfbay.redhat.com> <Pine.LNX.4.33.0207202158420.21322-100000@www.eyesopen.com> <20020721193843.GD22786@atrey.karlin.mff.cuni.cz>
On Sun, Jul 21, 2002 at 09:38:43PM +0200, Jan Hubicka wrote:
> This is really interesting case. The beggining of function contains:
> (insn 4 3 6 0 (nil) (set (reg:SI 62)
> (mem/f:SI (plus:SI (reg/f:SI 16 argp)
> (const_int 4 [0x4])) [4 y+0 S4 A32])) 45 {*movsi_1}
> (nil)
> (expr_list:REG_EQUIV (mem/f:SI (plus:SI (reg/f:SI 16 argp)
> (const_int 4 [0x4])) [4 y+0 S4 A32])
> (nil)))
>
> And later also:
>
> (insn 12 6 21 0 0x401a3a80 (set (reg/v/f:SI 64)
> (mem/f:SI (plus:SI (reg/f:SI 16 argp)
> (const_int 4 [0x4])) [4 S4 A8])) 45 {*movsi_1} (nil)
> (nil))
>
> cselib notices the equivalence and cprop actually does the replacement
> of reg 64 by reg 62. But the REG_EQUIV note is not really valid, as the
> value of memory copy y is not valid during the function (overwriten by
> bar call).
Your reasoning is incorrect. REG_EQUIV is a _local_ equivalence,
free to be killed at any moment. REG_EQUAL is the global equivalence.
Irritatingly, the test case isn't failing for me at the moment, so
I can't make any more progress here.
r~