[PATCH AARCH64]Make ldp/stp case less vulnerable

[PATCH AARCH64]Make ldp/stp case less vulnerable

[Bin Cheng]

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Hi,
Case gcc.target/aarch64/ldp_stp_3.c test fails on aarch64-none-elf.
Instead of merging the loads into ldp it generates:

foo:
         adrp    x1, .LANCHOR0
         add     x1, x1, :lo12:.LANCHOR0
         ldr     w0, [x1, 4]
         ldr     w3, [x1, 20]
         ldr     w2, [x1, 32]
         ldr     w1, [x1, 16]
         add     x2, x3, x2
         add     x0, x0, x1
         add     x0, x2, x0
         ret

Once register allocation decides to load [x1, 16] into x1(w1) like below:
    14: x0:DI = zero_extend([x1:DI+0x4])
     7: x3:DI = zero_extend([x1:DI+0x14])
    10: x2:DI = zero_extend([x1:DI+0x20])
    17: x1:DI = zero_extend([x1:DI+0x10])

Instructions 14/7/10 are anti-dependent on insn 17, bug sched_fusion orders
ready list (14/7/10) in ascending order of address.  As a result insn 10
intervenes between 7 and 17.
This patch fixes this by making cases less vulnerable.  One possible fix is
to move sched_fusion after regrename, it does help a lot.  I didn't do that
because regrenamre is currently disabled.

Tested on aarch64-elf.  Is it OK?

Thanks,
bin

gcc/testsuite/ChangeLog
2014-12-11  Bin Cheng  <bin.cheng@arm.com>

	* gcc.target/aarch64/ldp_stp_2.c: Make test less vulnerable.
	* gcc.target/aarch64/ldp_stp_3.c: Ditto.

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Index: gcc/testsuite/gcc.target/aarch64/ldp_stp_2.c
===================================================================
--- gcc/testsuite/gcc.target/aarch64/ldp_stp_2.c	(revision 218558)
+++ gcc/testsuite/gcc.target/aarch64/ldp_stp_2.c	(working copy)
@@ -7,10 +7,8 @@ long long
 foo ()
 {
   long long ll = 0;
-  ll += arr[0][1];
   ll += arr[1][0];
   ll += arr[1][1];
-  ll += arr[2][0];
   return ll;
 }
 
Index: gcc/testsuite/gcc.target/aarch64/ldp_stp_3.c
===================================================================
--- gcc/testsuite/gcc.target/aarch64/ldp_stp_3.c	(revision 218558)
+++ gcc/testsuite/gcc.target/aarch64/ldp_stp_3.c	(working copy)
@@ -7,10 +7,8 @@ unsigned long long
 foo ()
 {
   unsigned long long ll = 0;
-  ll += arr[0][1];
   ll += arr[1][0];
   ll += arr[1][1];
-  ll += arr[2][0];
   return ll;
 }
 

Re: [PATCH AARCH64]Make ldp/stp case less vulnerable

[Marcus Shawcroft]

On 11 December 2014 at 10:06, Bin Cheng <bin.cheng@arm.com> wrote:

> gcc/testsuite/ChangeLog
> 2014-12-11  Bin Cheng  <bin.cheng@arm.com>
>
>         * gcc.target/aarch64/ldp_stp_2.c: Make test less vulnerable.
>         * gcc.target/aarch64/ldp_stp_3.c: Ditto.

OK /Marcus