[PATCH][AArch64] Improve legitimize

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* [PATCH][AArch64] Improve legitimize_address
@ 2016-09-06 13:31 Wilco Dijkstra
  2016-09-07 12:59 ` Richard Earnshaw (lists)
  0 siblings, 1 reply; 4+ messages in thread
From: Wilco Dijkstra @ 2016-09-06 13:31 UTC (permalink / raw)
  To: GCC Patches; +Cc: nd

Improve aarch64_legitimize_address - avoid splitting the offset if it is
supported.  When we do split, take the mode size into account.  BLKmode
falls into the unaligned case but should be treated like LDP/STP.
This improves codesize slightly due to fewer base address calculations:

int f(int *p) { return p[5000] + p[7000]; }

Now generates:

f:
	add	x0, x0, 16384
	ldr	w1, [x0, 3616]
	ldr	w0, [x0, 11616]
	add	w0, w1, w0
	ret

instead of:

f:
	add	x1, x0, 16384
	add	x0, x0, 24576
	ldr	w1, [x1, 3616]
	ldr	w0, [x0, 3424]
	add	w0, w1, w0
	ret

OK for trunk?

ChangeLog:
2016-09-06  Wilco Dijkstra  <wdijkstr@arm.com>

    gcc/
	* config/aarch64/aarch64.c (aarch64_legitimize_address):
	Avoid use of base_offset if offset already in range.
--

diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
index 27bbdbad8cddc576f9ed4fd0670116bd6d318412..119ff0aecb0c9f88899fa141b2c7f9158281f9c3 100644
--- a/gcc/config/aarch64/aarch64.c
+++ b/gcc/config/aarch64/aarch64.c
@@ -5058,9 +5058,19 @@ aarch64_legitimize_address (rtx x, rtx /* orig_x  */, machine_mode mode)
       /* For offsets aren't a multiple of the access size, the limit is
 	 -256...255.  */
       else if (offset & (GET_MODE_SIZE (mode) - 1))
-	base_offset = (offset + 0x100) & ~0x1ff;
+	{
+	  base_offset = (offset + 0x100) & ~0x1ff;
+
+	  /* BLKmode typically uses LDP of X-registers.  */
+	  if (mode == BLKmode)
+	    base_offset = (offset + 512) & ~0x3ff;
+	}
+      /* Small negative offsets are supported.  */
+      else if (IN_RANGE (offset, -256, 0))
+	base_offset = 0;
+      /* Use 12-bit offset by access size.  */
       else
-	base_offset = offset & ~0xfff;
+	base_offset = offset & (~0xfff * GET_MODE_SIZE (mode));
 
       if (base_offset != 0)
 	{

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [PATCH][AArch64] Improve legitimize_address
  2016-09-06 13:31 [PATCH][AArch64] Improve legitimize_address Wilco Dijkstra
@ 2016-09-07 12:59 ` Richard Earnshaw (lists)
  2016-09-07 20:04   ` Christophe Lyon
  0 siblings, 1 reply; 4+ messages in thread
From: Richard Earnshaw (lists) @ 2016-09-07 12:59 UTC (permalink / raw)
  To: Wilco Dijkstra, GCC Patches; +Cc: nd

On 06/09/16 14:14, Wilco Dijkstra wrote:
> Improve aarch64_legitimize_address - avoid splitting the offset if it is
> supported.  When we do split, take the mode size into account.  BLKmode
> falls into the unaligned case but should be treated like LDP/STP.
> This improves codesize slightly due to fewer base address calculations:
> 
> int f(int *p) { return p[5000] + p[7000]; }
> 
> Now generates:
> 
> f:
> 	add	x0, x0, 16384
> 	ldr	w1, [x0, 3616]
> 	ldr	w0, [x0, 11616]
> 	add	w0, w1, w0
> 	ret
> 
> instead of:
> 
> f:
> 	add	x1, x0, 16384
> 	add	x0, x0, 24576
> 	ldr	w1, [x1, 3616]
> 	ldr	w0, [x0, 3424]
> 	add	w0, w1, w0
> 	ret
> 
> OK for trunk?
> 
> ChangeLog:
> 2016-09-06  Wilco Dijkstra  <wdijkstr@arm.com>
> 
>     gcc/
> 	* config/aarch64/aarch64.c (aarch64_legitimize_address):
> 	Avoid use of base_offset if offset already in range.

OK.

R.

> --
> 
> diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
> index 27bbdbad8cddc576f9ed4fd0670116bd6d318412..119ff0aecb0c9f88899fa141b2c7f9158281f9c3 100644
> --- a/gcc/config/aarch64/aarch64.c
> +++ b/gcc/config/aarch64/aarch64.c
> @@ -5058,9 +5058,19 @@ aarch64_legitimize_address (rtx x, rtx /* orig_x  */, machine_mode mode)
>        /* For offsets aren't a multiple of the access size, the limit is
>  	 -256...255.  */
>        else if (offset & (GET_MODE_SIZE (mode) - 1))
> -	base_offset = (offset + 0x100) & ~0x1ff;
> +	{
> +	  base_offset = (offset + 0x100) & ~0x1ff;
> +
> +	  /* BLKmode typically uses LDP of X-registers.  */
> +	  if (mode == BLKmode)
> +	    base_offset = (offset + 512) & ~0x3ff;
> +	}
> +      /* Small negative offsets are supported.  */
> +      else if (IN_RANGE (offset, -256, 0))
> +	base_offset = 0;
> +      /* Use 12-bit offset by access size.  */
>        else
> -	base_offset = offset & ~0xfff;
> +	base_offset = offset & (~0xfff * GET_MODE_SIZE (mode));
>  
>        if (base_offset != 0)
>  	{
> 

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [PATCH][AArch64] Improve legitimize_address
  2016-09-07 12:59 ` Richard Earnshaw (lists)
@ 2016-09-07 20:04   ` Christophe Lyon
  2016-09-08 11:56     ` Wilco Dijkstra
  0 siblings, 1 reply; 4+ messages in thread
From: Christophe Lyon @ 2016-09-07 20:04 UTC (permalink / raw)
  To: Richard Earnshaw (lists); +Cc: Wilco Dijkstra, GCC Patches, nd

Hi Wilco,

On 7 September 2016 at 14:43, Richard Earnshaw (lists)
<Richard.Earnshaw@arm.com> wrote:
> On 06/09/16 14:14, Wilco Dijkstra wrote:
>> Improve aarch64_legitimize_address - avoid splitting the offset if it is
>> supported.  When we do split, take the mode size into account.  BLKmode
>> falls into the unaligned case but should be treated like LDP/STP.
>> This improves codesize slightly due to fewer base address calculations:
>>
>> int f(int *p) { return p[5000] + p[7000]; }
>>
>> Now generates:
>>
>> f:
>>       add     x0, x0, 16384
>>       ldr     w1, [x0, 3616]
>>       ldr     w0, [x0, 11616]
>>       add     w0, w1, w0
>>       ret
>>
>> instead of:
>>
>> f:
>>       add     x1, x0, 16384
>>       add     x0, x0, 24576
>>       ldr     w1, [x1, 3616]
>>       ldr     w0, [x0, 3424]
>>       add     w0, w1, w0
>>       ret
>>
>> OK for trunk?
>>
>> ChangeLog:
>> 2016-09-06  Wilco Dijkstra  <wdijkstr@arm.com>
>>
>>     gcc/
>>       * config/aarch64/aarch64.c (aarch64_legitimize_address):
>>       Avoid use of base_offset if offset already in range.
>
> OK.
>
> R.

After this patch, I've noticed a regression:
FAIL: gcc.target/aarch64/ldp_vec_64_1.c scan-assembler ldp\td[0-9]+, d[0-9]
You probably need to adjust the scan pattern.

Thanks,

Christophe


>
>> --
>>
>> diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
>> index 27bbdbad8cddc576f9ed4fd0670116bd6d318412..119ff0aecb0c9f88899fa141b2c7f9158281f9c3 100644
>> --- a/gcc/config/aarch64/aarch64.c
>> +++ b/gcc/config/aarch64/aarch64.c
>> @@ -5058,9 +5058,19 @@ aarch64_legitimize_address (rtx x, rtx /* orig_x  */, machine_mode mode)
>>        /* For offsets aren't a multiple of the access size, the limit is
>>        -256...255.  */
>>        else if (offset & (GET_MODE_SIZE (mode) - 1))
>> -     base_offset = (offset + 0x100) & ~0x1ff;
>> +     {
>> +       base_offset = (offset + 0x100) & ~0x1ff;
>> +
>> +       /* BLKmode typically uses LDP of X-registers.  */
>> +       if (mode == BLKmode)
>> +         base_offset = (offset + 512) & ~0x3ff;
>> +     }
>> +      /* Small negative offsets are supported.  */
>> +      else if (IN_RANGE (offset, -256, 0))
>> +     base_offset = 0;
>> +      /* Use 12-bit offset by access size.  */
>>        else
>> -     base_offset = offset & ~0xfff;
>> +     base_offset = offset & (~0xfff * GET_MODE_SIZE (mode));
>>
>>        if (base_offset != 0)
>>       {
>>
>

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [PATCH][AArch64] Improve legitimize_address
  2016-09-07 20:04   ` Christophe Lyon
@ 2016-09-08 11:56     ` Wilco Dijkstra
  0 siblings, 0 replies; 4+ messages in thread
From: Wilco Dijkstra @ 2016-09-08 11:56 UTC (permalink / raw)
  To: Christophe Lyon, Richard Earnshaw; +Cc: GCC Patches, nd

Christophe Lyon wrote:
> After this patch, I've noticed a regression:
> FAIL: gcc.target/aarch64/ldp_vec_64_1.c scan-assembler ldp\td[0-9]+, d[0-9]
> You probably need to adjust the scan pattern.

The original code was better and what we should generate. IVOpt chooses to use
indexing eventhough it is more expensive, and that is a latent bug.

See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65068 which shows the same
cost calculation issue.

Wilco

^ permalink raw reply	[flat|nested] 4+ messages in thread

end of thread, other threads:[~2016-09-08 11:53 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2016-09-06 13:31 [PATCH][AArch64] Improve legitimize_address Wilco Dijkstra
2016-09-07 12:59 ` Richard Earnshaw (lists)
2016-09-07 20:04   ` Christophe Lyon
2016-09-08 11:56     ` Wilco Dijkstra

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