RE: [Patch/ARM] Cortex-M4 core pipeline patch to tune LDR/STR pairs

["Terry Guo" <terry dot guo at arm dot com>]

Hello Ramana,

Can you please review my patch at
http://gcc.gnu.org/ml/gcc-patches/2013-03/msg01252.html.

Thanks.

Terry

> -----Original Message-----
> From: gcc-patches-owner@gcc.gnu.org [mailto:gcc-patches-
> owner@gcc.gnu.org] On Behalf Of Terry Guo
> Sent: Friday, March 29, 2013 6:00 PM
> To: gcc-patches@gcc.gnu.org
> Subject: [Patch/ARM] Cortex-M4 core pipeline patch to tune LDR/STR pairs
> 
> Hello,
> 
> The attached pipeline patch intends to turn following code generation
> 
> ldr r5, [r4, #12]
> adds r2, r2, #16
> str r5, [r3, #8]
> 
> to
> 
> ldr r5, [r4, #12]
> str r5, [r3, #8]
> adds r2, r2, #16
> 
> The reason is that the STR can be started from the second cycle of its
> preceding LDR which takes 2 cycles, as long as the result of LDR isn't
used as
> memory address of STR.
> 
> Tested with various benchmarks on Cortex-M4 MPS. Except one regression
> caused by register allocation, the others either show performance
> improvement or no change.
> 
> Is it OK to trunk?
> 
> BR,
> Terry
> 
> 2013-03-29  Terry Guo  <terry.guo@arm.com>
> 
>                 * gcc/config/arm/cortex-m4.md: New bypass to tune LDR/STR
pairs.