1994190 - Simplify rounding instructions for riscv64

Status: RESOLVED FIXED

(Core :: JavaScript Engine: JIT, enhancement, P5)

Description

[André Bargull [:anba]]

And also perform the same changes for mips64 and loong64 for consistency.

Comment 1

[André Bargull [:anba]]

Attachment: Bug 1994190 - Part 1: Fix some comments in ARM64 MacroAssembler. r=#spidermonkey-reviewers!

"top word" was probably copied from ARM32, but doesn't reflect the ARM64 code.

Drive-by change:

• Remove unused variables.

Comment 2

[André Bargull [:anba]]

Attachment: Bug 1994190 - Part 2: Simplify rounding instructions for riscv64. r=#spidermonkey-reviewers!

This matches the approach used in ARM64 and requires less instructions, because
we no longer have to read from the fcsr register.

RISCV rounding instructions return INT64_{MIN,MAX} [1] for invalid inputs,
including NaN, so we can easily determine the error case by sign-extending
from 32-bit to 64-bit and then comparing against the conversion result.

[1] https://riscv.github.io/riscv-isa-manual/snapshot/unprivileged/#int_conv

Comment 3

[André Bargull [:anba]]

Attachment: Bug 1994190 - Part 3: Simplify rounding instructions for loong64. r=#spidermonkey-reviewers!

Perform the same changes for loong64.

This also ensures we don't bail for code like Math.floor(0x7fff_ffff) or
Math.floor(-0x8000_0000). (Similar for other rounding instructions.)

Comment 4

[André Bargull [:anba]]

Attachment: Bug 1994190 - Part 4: Simplify rounding instructions for mips64. r=#spidermonkey-reviewers!

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/4425f310c013
https://hg.mozilla.org/integration/autoland/rev/641baf8ffa54
Part 1: Fix some comments in ARM64 MacroAssembler. r=spidermonkey-reviewers,iain
https://github.com/mozilla-firefox/firefox/commit/ea235975dec5
https://hg.mozilla.org/integration/autoland/rev/0e10cacc0b66
Part 2: Simplify rounding instructions for riscv64. r=spidermonkey-reviewers,iain
https://github.com/mozilla-firefox/firefox/commit/dae7db185717
https://hg.mozilla.org/integration/autoland/rev/2964fd4af686
Part 3: Simplify rounding instructions for loong64. r=spidermonkey-reviewers,iain
https://github.com/mozilla-firefox/firefox/commit/5dbd7fb9849c
https://hg.mozilla.org/integration/autoland/rev/1b69a94373c3
Part 4: Simplify rounding instructions for mips64. r=spidermonkey-reviewers,iain

Comment 6

[pstanciu]

https://hg.mozilla.org/mozilla-central/rev/641baf8ffa54
https://hg.mozilla.org/mozilla-central/rev/0e10cacc0b66
https://hg.mozilla.org/mozilla-central/rev/2964fd4af686
https://hg.mozilla.org/mozilla-central/rev/1b69a94373c3