1995496 - Use div+mod sequence on risc64

Status: RESOLVED FIXED

(Core :: JavaScript Engine: JIT, enhancement, P3)

Description

[André Bargull [:anba]]

From https://riscv.github.io/riscv-isa-manual/snapshot/unprivileged/#_division_operations:

If both the quotient and remainder are required from the same division, the recommended code sequence is: DIV[U] rdq, rs1, rs2; REM[U] rdr, rs1, rs2 (rdq cannot be the same as rs1 or rs2). Microarchitectures can then fuse these into a single divide operation instead of performing two separate divides.

Comment 1

[André Bargull [:anba]]

Attachment: Bug 1995496 - Part 1: Use div+mod sequence on risc64. r=#spidermonkey-reviewers!

From https://riscv.github.io/riscv-isa-manual/snapshot/unprivileged/#_division_operations:

If both the quotient and remainder are required from the same division, the
recommended code sequence is: DIV[U] rdq, rs1, rs2; REM[U] rdr, rs1, rs2
(rdq cannot be the same as rs1 or rs2). Microarchitectures can then
fuse these into a single divide operation instead of performing two separate
divides.

Comment 2

[André Bargull [:anba]]

Attachment: Bug 1995496 - Part 2: Inline ma_div_branch_overflow into callers. r=#spidermonkey-reviewers!

The name ma_div_branch_overflow is misleading, because there's no "overflow".
Inlining the method also makes it easier to use the recommended div-mod
sequence on riscv64.

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/8a0ce9ee7a6a
https://hg.mozilla.org/integration/autoland/rev/5b73a2ab4c5e
Part 1: Use div+mod sequence on risc64. r=spidermonkey-reviewers,iain
https://github.com/mozilla-firefox/firefox/commit/1b30618ccf0f
https://hg.mozilla.org/integration/autoland/rev/2982d494fd3c
Part 2: Inline ma_div_branch_overflow into callers. r=spidermonkey-reviewers,iain

Comment 4

[Norisz Fay [:noriszfay]]

https://hg.mozilla.org/mozilla-central/rev/5b73a2ab4c5e
https://hg.mozilla.org/mozilla-central/rev/2982d494fd3c