1979829 - Ion's EAA pass: limit EffectiveAddress2 nodes to constants synthesisable in a single instruction.

Status: RESOLVED FIXED

(Core :: JavaScript: WebAssembly, enhancement, P2)

Description

[Julian Seward [:jseward]]

Ion's EAA pass can produce MEffectiveAddress2 nodes, which compute
constant +32 (index << {1,2,3}). On Intel that is fine; we can roll any
value of constant (an int32_t) into the resulting leal instruction. But
on arm64 (and all other targets) we have to synthesise it into a register,
which can take two instructions for larger values. That causes a perf
regression for JS3/gcc-loops-wasm.

Comment 1

[Julian Seward [:jseward]]

Attachment: Bug 1979829 - Ion's EAA pass: limit EffectiveAddress2 nodes to constants synthesisable in a single instruction. r=rhunt.

Ion's EAA pass can produce MEffectiveAddress2 nodes, which compute
constant +32 (index << {1,2,3}). On Intel that is fine; we can roll any
value of constant (an int32_t) into the resulting leal instruction. But
on arm64 (and all other targets) we have to synthesise it into a register,
which can take two instructions for larger values. That causes a perf
regression for JS3/gcc-loops-wasm.

This patch limits formation of MEffectiveAddress2 nodes to constant values
that we know the backend can synthesise into a register in at most one
instruction.

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/b905964ae5e7
https://hg.mozilla.org/integration/autoland/rev/7fafb4b912a8
Ion's EAA pass: limit EffectiveAddress2 nodes to constants synthesisable in a single instruction.  r=rhunt.

Comment 3

[Cristina Horotan [:chorotan]]

https://hg.mozilla.org/mozilla-central/rev/7fafb4b912a8