From 3f26f054872c375e7f9a80ede7a56036d9b57597 Mon Sep 17 00:00:00 2001 From: Wilco Dijkstra Date: Thu, 8 Feb 2018 12:32:51 +0000 Subject: [PATCH] [AArch64] Use more LDP/STP in shrinkwrapping The shrinkwrap optimization added in GCC 7 allows each callee-save to be delayed and done only across blocks which need a particular callee-save. Although this reduces unnecessary memory traffic on code paths that need few callee-saves, it typically uses LDR/STR rather than LDP/STP. This means more memory accesses and increased codesize, ~1.0% on average. To improve this, if a particular callee-save must be saved/restored, also add the adjacent callee-save to allow use of LDP/STP. This significantly reduces codesize (for example gcc_r, povray_r, parest_r, xalancbmk_r are 1% smaller). This is a simple fix which can be backported. A more advanced approach would scan blocks for pairs of callee-saves, but that requires a full rewrite of all the callee-save code which is too late at this stage. An example epilog in a shrinkwrapped function before: ldp x21, x22, [sp,#16] ldr x23, [sp,#32] ldr x24, [sp,#40] ldp x25, x26, [sp,#48] ldr x27, [sp,#64] ldr x28, [sp,#72] ldr x30, [sp,#80] ldr d8, [sp,#88] ldp x19, x20, [sp],#96 ret And after this patch: ldr d8, [sp,#88] ldp x21, x22, [sp,#16] ldp x23, x24, [sp,#32] ldp x25, x26, [sp,#48] ldp x27, x28, [sp,#64] ldr x30, [sp,#80] ldp x19, x20, [sp],#96 ret gcc/ * config/aarch64/aarch64.c (aarch64_components_for_bb): Increase LDP/STP opportunities by adding adjacent callee-saves. From-SVN: r257482 --- gcc/ChangeLog | 5 +++++ gcc/config/aarch64/aarch64.c | 17 ++++++++++++++++- 2 files changed, 21 insertions(+), 1 deletion(-) diff --git a/gcc/ChangeLog b/gcc/ChangeLog index c9a9fdb745e..ef2f46ef0d7 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,8 @@ +2018-02-08 Wilco Dijkstra + + * config/aarch64/aarch64.c (aarch64_components_for_bb): + Increase LDP/STP opportunities by adding adjacent callee-saves. + 2018-02-08 Wilco Dijkstra PR rtl-optimization/84068 diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c index 7c9c6e53169..228fd1b908d 100644 --- a/gcc/config/aarch64/aarch64.c +++ b/gcc/config/aarch64/aarch64.c @@ -4552,7 +4552,22 @@ aarch64_components_for_bb (basic_block bb) && (bitmap_bit_p (in, regno) || bitmap_bit_p (gen, regno) || bitmap_bit_p (kill, regno))) - bitmap_set_bit (components, regno); + { + unsigned regno2, offset, offset2; + bitmap_set_bit (components, regno); + + /* If there is a callee-save at an adjacent offset, add it too + to increase the use of LDP/STP. */ + offset = cfun->machine->frame.reg_offset[regno]; + regno2 = ((offset & 8) == 0) ? regno + 1 : regno - 1; + + if (regno2 <= LAST_SAVED_REGNUM) + { + offset2 = cfun->machine->frame.reg_offset[regno2]; + if ((offset & ~8) == (offset2 & ~8)) + bitmap_set_bit (components, regno2); + } + } return components; } -- 2.30.2