From: David Edelsohn <dje.gcc@gmail.com>
To: gcc-patches@gcc.gnu.org, Alan Modra <amodra@gmail.com>
Subject: Re: powerpc64 large-toc vs. reload
Date: Mon, 20 Jun 2011 08:06:00 -0000 [thread overview]
Message-ID: <BANLkTikKVH9hcc+9nv9ULPdzJXeDNuTdTg@mail.gmail.com> (raw)
In-Reply-To: <20110619140336.GM21332@bubble.grove.modra.org>
On Sun, Jun 19, 2011 at 10:03 AM, Alan Modra <amodra@gmail.com> wrote:
> I was alerted to a problem with large toc (-mcmodel=medium/large) code
> a few days ago by warnings emitted during a binutils build.
>
> dwarf.c: In function 'display_debug_lines_raw':
> dwarf.c:2409:1: note: non-delegitimized UNSPEC UNSPEC_TOCREL (44) found in variable location
> dwarf.c:2409:1: note: non-delegitimized UNSPEC UNSPEC_TOCREL (44) found in variable location
>
> On investigating why this was happening, I found that these UNSPECs
> were from the high part calculation of a toc-relative address that
> didn't get a register. reload allocated the pseudo to a stack slot..
> The stack slot didn't match the tight pattern in delegitimize_address
> which is why we have an UNSPEC left in the debug info. The real
> problem of course is that reload should never allocate a stack slot
> for a simple address calculation that can be rematerialised anywhere
> in the function with just one instruction. So after quite a bit of
> digging around in reload, I finally figured out that the problem has a
> really easy solution. Simply tell reload that those high part address
> calculations are constants. Which is true.
>
> That's what the create_TOC_reference change, and the rs6000.md changes
> below do. (I also fix large-toc tls patterns.) The rest of the patch
> just adjusts for the changed RTL.
>
> Bootstrap and regression tests powerpc64-linux in progress. OK to
> apply mainline and 4.6 assuming no regressions?
>
> * config/rs6000/rs6000.c (create_TOC_reference): Wrap high part
> of toc-relative address in CONST.
> (rs6000_delegitimize_address): Recognize changed address.
> (rs6000_legitimize_reload_address): Likewise.
> (rs6000_emit_move): Don't force these constants to memory.
> * config/rs6000/rs6000.md (tls_gd, tls_gd_high): Wrap high part of
> toc-relative address in CONST.
> (tls_ld, tls_ld_high, tls_got_dtprel, tls_got_dtprel_high): Likewise.
> (tls_got_tprel, tls_got_tprel_high, largetoc_high): Likewise.
Okay.
Thanks, David
next prev parent reply other threads:[~2011-06-20 3:04 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-06-19 18:15 Alan Modra
2011-06-20 8:06 ` David Edelsohn [this message]
2011-06-20 15:18 ` Alan Modra
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