Hello Jim, Appreciate for your comments. I will try to manually apply that patch on my side and try it. BTW, may I know which released Linaro gcc version include that patch? Maybe I can download it and try it quickly. https://gcc.gnu.org/ml/gcc-patches/2015-10/msg00025.html
Best Regards Ron -----Original Message----- From: Jim Wilson [mailto:jim.wil...@linaro.org] Sent: Wednesday, January 06, 2016 7:49 AM To: Xiaofeng Ren <xiaofeng....@nxp.com> Cc: Kugan <kugan.vivekanandara...@linaro.org>; Bernie Ogden <bernie.og...@linaro.org>; linaro-toolchain@lists.linaro.org Subject: Re: gcc-linaro-5.1 vs gcc-linaro-4.8 On Tue, Jan 5, 2016 at 5:52 AM, Xiaofeng Ren <xiaofeng....@nxp.com> wrote: >> Gcc-5.1: >> 40110c: 3dc00c6c ldr q12, [x3,#48] >> Gcc-4.8: >> 40135c: 4cdf78af ld1 {v15.4s}, [x5], #16 The ld1 and ldr instructions are effectively equivalent, they are both loading 16-byte values into fp/simd registers. I see a difference in the scheduling though. The gcc-4.8 output has a series of shift/add/store instructions while the gcc-5.1 output has a series of shift instructions followed by a series of store instructions. The gcc-5.1 output will serialize the code as these are simd shifts which can only execute one at a time, and stores can only execute one at a time. I see that gcc-4.8 has no cortex-a53 pipeline description, so we appear to be getting good code by accident. The gcc-5.1 has a cortex a53 scheduler, but it doesn't handle simd instructions, so it isn't scheduling them correctly. I see that there was a change added in November https://gcc.gnu.org/ml/gcc-patches/2015-10/msg00025.html that adds a new a53 pipeline description, and this one does handle simd instructions. With current sources, I see some shifts, alternating shifts and stores, and then the last of the stores. This should give better performance than the gcc-5.1 code. I haven't tried testing it on hardware. Jim _______________________________________________ linaro-toolchain mailing list linaro-toolchain@lists.linaro.org https://lists.linaro.org/mailman/listinfo/linaro-toolchain
