Based on micro-architectural testing of Spacemit-X60 ALU instructions
they reserve only one of the two ALU units available on the CPU.
Modeling the reservation of ALU instructions as ALU0 or ALU1 moves the
needle slightly.
Benchmark of coremark executed with perf:
taskset -c 0 perf stat -r 10 -e cycles,instructions ./coremark.exe
-mtune=spacemit-x60 -march=rv64gc_zba_zbb_zbs -O2
current new
cycles 29,442,732,143 +-0.11% 28,892,288,831 +-0.07%
insns 31,451,155,580 +-0.03% 31,450,458,048 +-0.03%
IPC 1.07 1.09
time (s) 18.4061 +-0.0209 18.0631 +-0.0131
-mcpu=spacemit-x60 -O2
current new
cycles 29,715,461,331 +-0.11% 29,622,701,777 +-0.10%
insns 29,679,069,220 +-0.03% 29,678,356,566 +-0.03%
IPC 1.00 1.00
time (s) 18.5767 +-0.0203 18.5192 +-0.0191
-mcpu=spacemit-x60 -O2 -funroll-loops
current new
cycles 28,212,445,245 +-0.12% 27,933,417,579 +-0.07%
Insns 29,604,622,477 +-0.03% 29,596,231,318 +-0.02%
IPC 1.05 1.06
time (s) 17.6383 +-0.0206 17.4639 +-0.0113
As one would expect, the greatest impact of this change is with the vector
instructions removed from the -march parameter.
Once loop unrolling is included along with vector instructions, this gives
extra scalar instructions for the scheduler to move around and the impact
of the change is more apparent.
2026-10-12 Dusan Stojkovic <[email protected]>
gcc/ChangeLog:
config/riscv/spacemit-x60.md (spacemit_x60_alu0, spacemit_x60_alu1):
((spacemit_x60_alu0|spacemit_x60_alu1)): update ALU reservation
definition.
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---
gcc/config/riscv/spacemit-x60.md | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/gcc/config/riscv/spacemit-x60.md b/gcc/config/riscv/spacemit-x60.md
index f23265ad380..702fc3cfefc 100644
--- a/gcc/config/riscv/spacemit-x60.md
+++ b/gcc/config/riscv/spacemit-x60.md
@@ -42,7 +42,7 @@
(define_cpu_unit "spacemit_x60_fdivsqrt" "spacemit_x60")
(define_reservation "spacemit_x60_lsu" "spacemit_x60_lsu0, spacemit_x60_lsu1")
-(define_reservation "spacemit_x60_alu" "spacemit_x60_alu0, spacemit_x60_alu1")
+(define_reservation "spacemit_x60_alu" "(spacemit_x60_alu0|spacemit_x60_alu1)")
;; ----------------------------------------------------
;; Memory (load/store)
--
2.34.1
