[Bug target/114978] [14/15 regression] 548.exchange2_r 14%-28% regressions on Loongarch64 after gcc 14 snapshot 20240317

["chenglulu at loongson dot cn" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114978

--- Comment #8 from chenglulu <chenglulu at loongson dot cn> ---
(In reply to Chen Chen from comment #0)
> We tested Loongarch64 CPU Loongson 3A6000 with "LA664" architecture in Linux
> operating system AOSC OS 11.4.0 (default gcc version is 13.2.0). And we
> found the 548.exchange2_r benchmark from SPEC 2017 INTrate suite suffered
> significant regressions from 14% to 28% with various compiling options.
> 
> The rate-1 results are following:
> 
/* snip */
> 
> after snapshot 20240317 score 18-23.1% lower with parameters "-g -Ofast
> -march=la664":       
> 13.2.0:    "-march=la664" flag is not supported
> 20240317:  11.5 (227s)
> 20240324:  8.84 (296s)
> 20240430:  9.43 (278s)
> 14.1.0:    9.42 (278s)
> 
/* snip */
> 
> 
> after snapshot 20240317 score 26.3-26.6% lower with parameters "-g -Ofast
> -march=la464":       
> 13.2.0:    8.76 (299s)
> 20240317:  12.8 (205s)
> 20240324:  9.39 (279s)
> 20240430:  9.43 (278s)
> 14.1.0:    9.43 (278s)
> 
> 

> 20240317:  11.5 (227s) -march=la664
> 20240317:  12.8 (205s) -march=la464
I looked for the reason for the gap between the above two results. The
performance regression is caused by r14-6814. If the following modifications
are made, the scores of -march=la664 and -march464 will be the same.

diff --git a/gcc/config/loongarch/loongarch-def.cc
b/gcc/config/loongarch/loongarch-def.cc
index e8c129ce643..f27284cb20a 100644
--- a/gcc/config/loongarch/loongarch-def.cc
+++ b/gcc/config/loongarch/loongarch-def.cc
@@ -111,11 +111,7 @@ loongarch_rtx_cost_data::loongarch_rtx_cost_data ()
  tune targets (i.e. -mtune=native while PRID does not correspond to
  any known "-mtune" type).  */
 array_tune<loongarch_rtx_cost_data> loongarch_cpu_rtx_cost_data =
-  array_tune<loongarch_rtx_cost_data> ()
-    .set (CPU_LA664,
-         loongarch_rtx_cost_data ()
-           .movcf2gr_ (COSTS_N_INSNS (1))
-           .movgr2cf_ (COSTS_N_INSNS (1)));
+  array_tune<loongarch_rtx_cost_data> ();