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Re: [4.9 PATCH, alpha]: Switch alpha to LRA
- From: Chung-Ju Wu <jasonwucj at gmail dot com>
- To: Steven Bosscher <stevenb dot gcc at gmail dot com>
- Cc: Jeff Law <law at redhat dot com>, Uros Bizjak <ubizjak at gmail dot com>, Richard Henderson <rth at redhat dot com>, "gcc-patches at gcc dot gnu dot org" <gcc-patches at gcc dot gnu dot org>, Vladimir Makarov <vmakarov at redhat dot com>
- Date: Thu, 25 Apr 2013 16:04:43 +0800
- Subject: Re: [4.9 PATCH, alpha]: Switch alpha to LRA
- References: <CAFULd4be3azVdXQhpnQE7Qee8350480TdQM1woUnNuav3Ehw9g at mail dot gmail dot com> <51070AFC dot 9060200 at redhat dot com> <CAFULd4aYwsf2xpwbuMznNWE5q35BaCuoG=uB3UUkSvFDOVamfg at mail dot gmail dot com> <51757484 dot 4000608 at redhat dot com> <CABu31nOsM_f4mJ7cV6K8__WqBHGTCkUwHEihtyvsgbvVoG1vTw at mail dot gmail dot com>
2013/4/23 Steven Bosscher <firstname.lastname@example.org>:
> On Mon, Apr 22, 2013 at 7:33 PM, Jeff Law wrote:
>> On 04/22/2013 11:17 AM, Uros Bizjak wrote:
>>> On Tue, Jan 29, 2013 at 12:34 AM, Richard Henderson <email@example.com>
>>>> On 01/28/2013 03:14 PM, Uros Bizjak wrote:
>>>>> 2013-01-28 Uros Bizjak<firstname.lastname@example.org>
>>>>> * config/alpha/alpha.c (TARGET_LRA_P): New define.
>>>>> Bootstrapped and regression tested  on alphaev68-unknown-linux-gnu.
>>>>> OK for 4.9?
>>> Unfortunately, alphas are much more tied to reload than it was hoped.
>>> While latest alphas (with FIX and BWX ISAs) survived transition to LRA
>>> without problems, further testing on ev4 and ev5 triggered various
>>> problems, one of them is PR57032  that exposed rather unique way of
>>> handling aligned/nonaligned memory operands.
>>> The patch was reverted.
>>> I suspect that fixing older alphas to live with LRA would be quite
>>> involved task, and I guess nobody (including me) wants to spend
>>> considerable amount of time on a dying architecture. Consequently,
>>> this also means that alphas will die together with reload as far as
>>> gcc is concerned.
>>>  http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57032
>> Would it make sense to deprecate the older Alpha implementations without
>> killing the "modern" ones?
> Right. That would also eliminate the NOTE_INSN_EH_REGION notes bug (PR
> I think it would be a shame to not enable LRA on alpha. It will only
> be another excuse to never let reload die, and it will hurt stability
> and reliability for Alpha EV6 in the long term as other targets switch
> over to LRA.
> Is it possible to add some EV4/EV5 splitters to work around this Alpha
> EV4/EV5 oddity? Even if it comes at a code quality cost, it's IMHO
> still better than tying the fate of apha to reload and vice versa..
How about using follow constraints?
--- alpha.c (revision 198216)
+++ alpha.c (working copy)
@@ -9871,6 +9871,9 @@
#define TARGET_LEGITIMATE_ADDRESS_P alpha_legitimate_address_p
+#define TARGET_LRA_P hook_bool_void_true
#define TARGET_CONDITIONAL_REGISTER_USAGE alpha_conditional_register_usage
--- alpha.md (revision 198216)
+++ alpha.md (working copy)
@@ -4073,9 +4073,9 @@
[(set (match_operand:DI 0 "nonimmediate_operand"
- "=r,r,r,r,r,r,r,r, m, *f,*f, Q, r,*f")
+ "=r,r,r,r,r,r,r,r, m, *f,*f, m, r,*f")
(match_operand:DI 1 "input_operand"
- "rJ,K,L,T,s,n,s,m,rJ,*fJ, Q,*f,*f, r"))]
+ "rJ,K,L,T,s,n,s,m,rJ,*fJ, m,*f,*f, r"))]
"register_operand (operands, DImode)
|| reg_or_0_operand (operands, DImode)"
As Uros said, the 'Q' is ignored by LRA.
The reason is that the predicate function normal_memory_operand()
may change op to a memory location by using resolved_reload_operand().
However, if LRA is enabled, resolve_reload_operand() always returns
original reg op because reload_in_progress would never be true,
resulting reload loop in this case.
So I guess using 'm' constraint instead of 'Q' is able to avoid
such abnormal behavior, leaving all the reload jobs to LRA.
IMHO that is a simplest solution. At least it passes the case in
and successfully build libgcc.