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Re: [PATCH] Improve i?86 address delegitimization after 32-bit pic changes (PR target/63542)

From: Jeff Law <law at redhat dot com>
To: Jakub Jelinek <jakub at redhat dot com>, Uros Bizjak <ubizjak at gmail dot com>
Cc: Ilya Enkovich <enkovich dot gnu at gmail dot com>, Vladimir Makarov <vmakarov at redhat dot com>, gcc-patches <gcc-patches at gcc dot gnu dot org>, Evgeny Stupachenko <evstupac at gmail dot com>, Richard Biener <richard dot guenther at gmail dot com>, Petr Machata <pmachata at redhat dot com>
Date: Wed, 22 Oct 2014 02:01:30 +0000
Subject: Re: [PATCH] Improve i?86 address delegitimization after 32-bit pic changes (PR target/63542)
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On 10/21/14 16:03, Jakub Jelinek wrote:

On Mon, Sep 29, 2014 at 01:08:56PM +0200, Jakub Jelinek wrote:

I wonder if during/after reload we just couldn't look at
ORIGINAL_REGNO of hard regs if ix86_use_pseudo_pic_reg.  Or is that
the other case, where you don't have any PIC register replacement around,
and want to subtract something?  Perhaps in that case we could just
subtract the value of _GLOBAL_OFFSET_TABLE_ symbol if we have nothing better
around.


Here is a patch that implements both of these ideas.

The number of lines like:
note: non-delegitimized UNSPEC UNSPEC_GOT (0) found in variable location
note: non-delegitimized UNSPEC UNSPEC_GOTOFF (1) found in variable location
during i686-linux bootstrap (not including regtest) went down from
14165 to 19.

The patch trusts that a hard reg with ORIGINAL_REGNO containing the pic
pseudo contains the _GLOBAL_OFFSET_TABLE_ value of the current shared
library (or binary), I think that is reasonable assumption.
And for ELF for the UNSPEC_GOTOFF it worse case can subtract
_GLOBAL_OFFSET_TABLE_ symbol if it doesn't know what register to subtract.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2014-10-21  Jakub Jelinek  <jakub@redhat.com>

	PR target/63542
	* config/i386/i386.c (ix86_pic_register_p): Also return
	true if x is a hard register with ORIGINAL_REGNO equal to
	pic_offset_table_rtx pseudo REGNO.
	(ix86_delegitimize_address): For ix86_use_pseudo_pic_reg ()
	after reload, subtract GOT_SYMBOL_NAME symbol if possible.

	* gcc.target/i386/pr63542-1.c: New test.
	* gcc.target/i386/pr63542-2.c: New test.

OK.
Jeff

References:
- [PATCH] Improve i?86 address delegitimization after 32-bit pic changes (PR target/63542)
  - From: Jakub Jelinek

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