[AArch64] Generate load-pairs when the last load clobbers the address register [2/2]

[Sudakshina Das]

Hi Jackson


On Tuesday 10 July 2018 09:37 AM, Jackson Woodruff wrote:
> Hi all,
>
> This patch resolves PR86014.  It does so by noticing that the last 
> load may clobber the address register without issue (regardless of 
> where it exists in the final ldp/stp sequence).  That check has been 
> changed so that the last register may be clobbered and the testcase 
> (gcc.target/aarch64/ldp_stp_10.c) now passes.
>
> Bootstrap and regtest OK.
>
> OK for trunk?
>
> Jackson
>
> Changelog:
>
> gcc/
>
> 2018-06-25  Jackson Woodruff  <jackson.woodruff@arm.com>
>
> Â Â Â Â Â Â Â  PR target/86014
> Â Â Â Â Â Â Â  * config/aarch64/aarch64.c 
> (aarch64_operands_adjust_ok_for_ldpstp):
> Â Â Â Â Â Â Â  Remove address clobber check on last register.
>
This looks good to me but you will need a maintainer to approve it. The only
thing I would add is that if you could move the comment on top of the 
for loop
to this patch. That is, keep the original
/* Check if the addresses are clobbered by load.  */
in your [1/2] and make the comment change in [2/2].

diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
index d0e9b2d464183eecc8cc7639ca3e981d2ff243ba..feffe8ebdbd4efd0ffc09834547767ceec46f4e4 100644
--- a/gcc/config/aarch64/aarch64.c
+++ b/gcc/config/aarch64/aarch64.c
@@ -17074,7 +17074,7 @@ aarch64_operands_adjust_ok_for_ldpstp (rtx *operands, bool load,
    /* Only the last register in the order in which they occur
       may be clobbered by the load.  */
    if (load)
-    for (int i = 0; i < num_instructions; i++)
+    for (int i = 0; i < num_instructions - 1; i++)
        if (reg_mentioned_p (reg[i], mem[i]))
  	return false;


Thanks
Sudi