From: Bernd Edlinger <bernd.edlinger@hotmail.de>
To: Jeff Law <law@redhat.com>,
"gcc-patches@gcc.gnu.org" <gcc-patches@gcc.gnu.org>
Subject: Re: [PATCH][ PR rtl-optimization/79286] Drop may_trap_p exception to testing dominance in update_equiv_regs
Date: Fri, 28 Apr 2017 18:05:00 -0000 [thread overview]
Message-ID: <AM4PR0701MB2162813D9C53F9CE4A39D624E4130@AM4PR0701MB2162.eurprd07.prod.outlook.com> (raw)
In-Reply-To: <464887c0-7474-b0c2-6c99-e539859c1642@redhat.com>
On 04/28/17 18:48, Jeff Law wrote:
> On 04/23/2017 05:54 AM, Bernd Edlinger wrote:
>> Hi Jeff,
>>
>>
>> this patch tries to fix the handling of pic_offset_rtx +
>> const(unspec(symbol_ref)+ const_int) in may_trap_p,
>> and restores the original state of affairs in update_equiv_regs.
>>
>>
>> What do you think is it OK to extract the symbol_ref out
>> of the unspec in this way, or is does it need a target hook?
>>
>>
>> Patch works at least for x86_64 and arm.
>> Is it OK for trunk?
>>
>>
>> Bernd.
>>
>>
>> patch-pr79286.diff
>>
>>
>> 2017-04-23 Bernd Edlinger<bernd.edlinger@hotmail.de>
>>
>> rtl-optimizatoin/79286
>> * ira.c (update_equiv_regs): Revert to using may_tap_p again.
>> * rtlanal.c (rtx_addr_can_trap_p_1): SYMBOL_REF_FUNCTION_P
>> can never
>> trap. Extract constant offset from pic_offset_table_rtx +
>> const(unspec(symbol_ref)+int_val) and pic_offset_table_rtx +
>> const(unspec(symbol_ref)), otherwise RTL may trap.
> ISTM that rtx_addr_can_trap_p_1 is fundamentally broken in that
> references via pic_offset_table_rtx can certainly trap.
>
> Whether or not a given reference traps is a function of the size of
> table (not known until link time) and the CONST_INT within the address
> expression. So I'd be more inclined to remove the special casing of PIC
> addresses where entirely -- that seemed pretty risky during stage3, but
> now would be an appropriate time to tackle that.
>
> If we were to try and keep the special handling, you certainly can't
> depend on the form looking like (const(unspec(symbol_ref) + const_int).
>
> You could have high/lo_sums were and probably other forms too. We allow
> the backends to largely define what PIC address looks like.
>
Yes I agree, that is probably not worth it. So I could try to remove
the special handling of PIC+const and see what happens.
However the SYMBOL_REF_FUNCTION_P is another story, that part I would
like to keep: It happens quite often, already w/o -fpic that call
statements are using SYMBOL_REFs to ordinary (not weak) function
symbols, and may_trap returns 1 for these call statements wihch is IMHO
wrong.
Bernd.
next prev parent reply other threads:[~2017-04-28 17:27 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-23 18:33 Bernd Edlinger
2017-04-28 17:17 ` Jeff Law
2017-04-28 18:05 ` Bernd Edlinger [this message]
2017-04-28 19:01 ` Jeff Law
2017-04-28 20:23 ` Bernd Edlinger
2017-04-28 20:27 ` Bernd Edlinger
2017-04-29 9:27 ` Bernd Edlinger
2017-05-12 16:49 ` [PING][PATCH][ " Bernd Edlinger
2017-06-01 16:00 ` [PING**2][PATCH][ " Bernd Edlinger
[not found] ` <59f99a5b-e5db-7078-5f55-c4b42f9c4a8b@hotmail.de>
2017-06-14 12:43 ` [PING**3][PATCH][ " Bernd Edlinger
2017-06-23 4:35 ` [PATCH][ " Jeff Law
-- strict thread matches above, loose matches on Subject: below --
2017-02-24 15:48 Jeff Law
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