https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104719
Jason Merrill <jason at gcc dot gnu.org> changed:
What |Removed |Added
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CC| |jason at gcc dot gnu.org
--- Comment #12 from Jason Merrill <jason at gcc dot gnu.org> ---
(In reply to Vittorio Romeo from comment #9)
> - For the `operator[]` benchmark, when using `-Og` after applying
> `[[gnu::always_inline]]` to all the functions touched by the benchmark, we
> reduce the overhead from 34% to around 11%.
Quoting from your gist:
-Og, without `[[gnu::always_inline]]` on `operator[]`
carray_squareop_mean 440 ns 439 ns 3
vector_squareop_mean 661 ns 662 ns 3
-Og, with `[[gnu::always_inline]]` on `operator[]`
vector_squareop_mean 494 ns 491 ns 3
Which looks significant...
...but I don't see this when I run your test myself; the vector_squareop
results (and the generated code) are unaffected by adding always_inline. In
particular there are no calls to operator[].
carray_squareop 547 ns 546 ns 1272023
vector_squareop 591 ns 589 ns 1227215
carray:
movslq %edx, %rax
leaq (%rbx,%rax,4), %rcx
movl (%rcx), %eax
addl $1, %eax
movl %eax, (%rcx)
movl %eax, (%rcx)
addl $1, %edx
vector:
movslq %ecx, %rax
salq $2, %rax
addq (%rsp), %rax
movl (%rax), %esi
leal 1(%rsi), %edx
movl %edx, (%rax)
movl %edx, (%rax)
addl $1, %ecx
It seems the main difference between the two is that the vector version needs
to keep loading the base pointer from the stack (%rsp) for some reason, rather
than keep it in a register %rbx. This doesn't seem like an inlining issue at
all.
The double move in both versions is curious.
