On 2023/4/18 20:45, Xi Ruoyao wrote:
On Tue, 2023-04-18 at 20:39 +0800, WANG Xuerui wrote:
Hi,
Thanks for helping confirming on GCC and porting this! I'd never know
even GCC lacked this adaptation without someone actually checking... Too
many things are taken for granted these days.
On 2023/4/18 20:17, Xi Ruoyao wrote:
According to Xuerui's LLVM changeset [1], doing so can make a
significant performace gain.
"doing so can gain significant performance" or "significant performance
can be gained by ..."?
Also the other important thing is, guaranteeing alignment also makes
performance *more predictable* in addition to generally making things
faster. You may want to mention this too somewhere.
Bootstrapped and regtested on loongarch64-linux-gnu. Ok for GCC 14?
[1]:https://reviews.llvm.org/D148622
nit: one space after the colon.
gcc/ChangeLog:
* config/loongarch/loongarch.cc
(loongarch_option_override_internal): If -falign-functions is
used but the alignment is not explicitly specified, set it to
4 * loongarch_issue_rate (). Likewise for -falign-loops.
---
gcc/config/loongarch/loongarch.cc | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/gcc/config/loongarch/loongarch.cc
b/gcc/config/loongarch/loongarch.cc
index 06fc1cd0604..6552484de7c 100644
--- a/gcc/config/loongarch/loongarch.cc
+++ b/gcc/config/loongarch/loongarch.cc
@@ -6236,6 +6236,17 @@ loongarch_option_override_internal (struct gcc_options
*opts)
&& !opts->x_optimize_size)
opts->x_flag_prefetch_loop_arrays = 1;
+ /* Align functions and loops to (issue rate) * (insn size) to improve
+ the throughput of the fetching units. */
What about gating all of these on !opts->x_optimize_size, similar to
what aarch64 does?
opts->x_flag_align_functions and opts->x_flag_align_loops are only set
with -O2 or above unless the user manually uses -falign-functions or -
falign-loops. If the user uses "-Os -falign-functions" as CFLAGS I'd
assume s(he) wants to optimize for size but keep the optimized function
alignment.
Ah, okay. Fine then.
BTW I've also added some comments to the commit message that I forgot to
review earlier.
+ char *align = XNEWVEC (char, 16);
+ sprintf (align, "%d", loongarch_issue_rate () * 4);
+
+ if (opts->x_flag_align_functions && !opts->x_str_align_functions)
+ opts->x_str_align_functions = align;
+
+ if (opts->x_flag_align_loops && !opts->x_str_align_loops)
+ opts->x_str_align_loops = align;
+
if (TARGET_DIRECT_EXTERN_ACCESS && flag_shlib)
error ("%qs cannot be used for compiling a shared library",
"-mdirect-extern-access");
Otherwise LGTM, thanks!
