1823857 - Minor tuning for wasm-gc code running on the arm64 simulator

Status: RESOLVED FIXED

(Core :: JavaScript: WebAssembly, enhancement, P3)

Description

[Julian Seward [:jseward]]

Wasm-gc code (compiled by baseline) on the arm64 simulator runs
very slowly; a factor of 500 slowdown compared to natively. Here are
two minor fixes which improve performance marginally.

• Code::lookupTrap: lift uint32_t target = ((uint8_t*)pc) - segment(t).base()
  out of a loop in which it is invariant; the compiler does not appear to do so.

• The arm64 simulator: inline a couple of small routines which are very
  hot -- used for every simulated memory access.

Comment 1

[Julian Seward [:jseward]]

Attachment: Bug 1823857 - part 1: Code::lookupTrap: lift an invariant expression out of a hot loop. r=rhunt.

Code::lookupTrap has

uint32_t target = ((uint8_t*)pc) - segment(t).base();

in a loop in which it is invariant. This patch lifts it out of the loop since
the clang++ 15.0.7 does not appear to do so, even at -O2. Reduces (host)
instruction count by around 10% on some artificial small wasm-gc tests.

Comment 2

[Julian Seward [:jseward]]

Attachment: Bug 1823857 - part 2: arm64 simulator: inline a couple of small routines that are hot. r=rhunt.

The routines are used for loads and stores, so this minor improvement is
widely applicable. Reduces (host) instruction count by around 2% for
wasm-baseline generated arm64 code.

Depends on D173275

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/774db827a9db
part 1: Code::lookupTrap: lift an invariant expression out of a hot loop.  r=rhunt.
https://hg.mozilla.org/integration/autoland/rev/91aab2296ba3
part 2: arm64 simulator: inline a couple of small routines that are hot.  r=rhunt.

Comment 4

[Sandor Molnar[:smolnar]]

https://hg.mozilla.org/mozilla-central/rev/774db827a9db
https://hg.mozilla.org/mozilla-central/rev/91aab2296ba3