From: James Greenhalgh <james.greenhalgh@arm.com>
To: Kyrill Tkachov <kyrylo.tkachov@foss.arm.com>
Cc: GCC Patches <gcc-patches@gcc.gnu.org>,
Marcus Shawcroft <marcus.shawcroft@arm.com>,
Richard Earnshaw <Richard.Earnshaw@arm.com>, <nd@arm.com>
Subject: Re: [PATCH][AArch64] Allow const0_rtx operand for atomic compare-exchange patterns
Date: Tue, 06 Jun 2017 13:16:00 -0000 [thread overview]
Message-ID: <20170606131621.GC2208@arm.com> (raw)
In-Reply-To: <58B56D3E.3090704@foss.arm.com>
On Tue, Feb 28, 2017 at 12:29:50PM +0000, Kyrill Tkachov wrote:
> Hi all,
>
> For the testcase in this patch we currently generate:
> foo:
> mov w1, 0
> ldaxr w2, [x0]
> cmp w2, 3
> bne .L2
> stxr w3, w1, [x0]
> cmp w3, 0
> .L2:
> cset w0, eq
> ret
>
> Note that the STXR could have been storing the WZR register instead of moving zero into w1.
> This is due to overly strict predicates and constraints in the store exclusive pattern and the
> atomic compare exchange expanders and splitters.
> This simple patch fixes that in the patterns concerned and with it we can generate:
> foo:
> ldaxr w1, [x0]
> cmp w1, 3
> bne .L2
> stxr w2, wzr, [x0]
> cmp w2, 0
> .L2:
> cset w0, eq
> ret
>
>
> Bootstrapped and tested on aarch64-none-linux-gnu.
> Ok for GCC 8?
OK.
Thanks,
James
> 2017-02-28 Kyrylo Tkachov <kyrylo.tkachov@arm.com>
>
> * config/aarch64/atomics.md (atomic_compare_and_swap<mode> expander):
> Use aarch64_reg_or_zero predicate for operand 4.
> (aarch64_compare_and_swap<mode> define_insn_and_split):
> Use aarch64_reg_or_zero predicate for operand 3. Add 'Z' constraint.
> (aarch64_store_exclusive<mode>): Likewise for operand 2.
>
> 2017-02-28 Kyrylo Tkachov <kyrylo.tkachov@arm.com>
>
> * gcc.target/aarch64/atomic_cmp_exchange_zero_reg_1.c: New test.
next prev parent reply other threads:[~2017-06-06 13:16 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-28 12:59 Kyrill Tkachov
2017-04-24 9:40 ` Kyrill Tkachov
2017-05-08 11:00 ` Kyrill Tkachov
2017-06-01 14:02 ` Kyrill Tkachov
2017-06-06 13:16 ` James Greenhalgh [this message]
2017-06-20 5:06 ` Andrew Pinski
2017-06-20 8:30 ` Kyrill Tkachov
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