[Patch AArch64] Add early clobber for the store_exclusive patterns.

[Ramana Radhakrishnan]

Hi,


I've had this in my patch stack after discovering the gas issue where we
weren't warning on cases that were unpredictable according to the
architecture.

I would like to backport this fix to earlier GCC branches too. I did a
few attempts but I haven't been able to trigger the unpredictable behaviour.

Bootstrapped and regression tested on AArch64 , no regressions.

Ok ?

Thanks,
Ramana


* config/aarch64/atomics.md (aarch64_store_exclusive<mode>): Add early
clobber.

commit 0608cb64b97368dc1bbea87e3a9541cfb832c015
Author: Ramana Radhakrishnan <ramana.radhakrish...@arm.com>
Date:   Tue Jun 12 16:03:24 2018 +0100

    [Patch AArch64] Add early clobber for aarch64_store_exclusive.

diff --git a/gcc/config/aarch64/atomics.md b/gcc/config/aarch64/atomics.md
index 68dc65c..cd8c44e 100644
--- a/gcc/config/aarch64/atomics.md
+++ b/gcc/config/aarch64/atomics.md
@@ -530,7 +530,7 @@
 )
 
 (define_insn "aarch64_store_exclusive<mode>"
-  [(set (match_operand:SI 0 "register_operand" "=r")
+  [(set (match_operand:SI 0 "register_operand" "=&r")
     (unspec_volatile:SI [(const_int 0)] UNSPECV_SX))
    (set (match_operand:ALLI 1 "aarch64_sync_memory_operand" "=Q")
     (unspec_volatile:ALLI