807185 - IonMonkey: optimize the non-native test in visitCallGeneric

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Luke Wagner [:luke]]

In the earlier JSFunction days you had to mask flags with JSFUN_KINDMASK and then compare against JSFUN_INTERPRETED.  Now that that gunk has been cleared, JSFUN_INTERPRETED is a single bit and can be tested directly.  dvander said this code was hot (hence the custom load16ZeroExtend_mask which could now be removed).  Ideally, I think, we'd load an (aligned) 32-bit word (at offset 0 in JSFunction) and test JSFUN_INTERPRETED bit shifted appropriately).

Comment 1

[Luke Wagner [:luke]]

I forgot to mention, there is the same test in visitApplyArgsGeneric.

Comment 2

[Sean Stangl [:sstangl]]

Great! Good good good.

Since no code requires |flags| after this test, on x86 and x86_64, where TEST exists with signature r/m32,r32 (or r/m32,i32), we could even perform the test without loading into a register.

Comment 3

[Luke Wagner [:luke]]

Attachment: patch

I can see a distinct 2-3% speedup on a micro-benchmark that has a polymorphic callsite.  SS and V8 seem unaffected.

Comment 4

[Luke Wagner [:luke]]

Oh yeah, this applies on top of bug 807228.

Comment 5

[Sean Stangl [:sstangl]]

Comment on attachment 677237 [details] [diff] [review]
patch

Review of attachment 677237 [details] [diff] [review]:
-----------------------------------------------------------------

::: js/src/ion/IonMacroAssembler.h
@@ +269,5 @@
> +        // 16-bit loads are slow and unaligned 32-bit loads may be too so
> +        // perform an aligned 32-bit load and adjust the bitmask accordingly.
> +        JS_STATIC_ASSERT(offsetof(JSFunction, nargs) % sizeof(uint32_t) == 0);
> +        JS_STATIC_ASSERT(offsetof(JSFunction, flags) == offsetof(JSFunction, nargs) + 2);
> +        JS_STATIC_ASSERT(IS_LITTLE_ENDIAN);

These asserts are extremely thorough. Hopefully, future modifications to this file will use them as an example.

Comment 6

[Luke Wagner [:luke]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/2628f57bdd4b

Comment 7

[Ed Morley [:emorley]]

https://hg.mozilla.org/mozilla-central/rev/2628f57bdd4b