1435369 - Implement non-trapping floating-point conversion proposal

Status: RESOLVED FIXED

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

Description

[Dan Gohman [:sunfish]]

Attachment: nontrapping.patch

Attached is a work-in-progress patch for the non-trapping float-to-int conversion proposal [0], which is in the Implementation Phase. So far, this includes platform-independent code and x64 support (Baseline and Ion). The feature is controlled by a compile-time flag which is only enabled on Nightly.

[0] https://github.com/WebAssembly/nontrapping-float-to-int-conversions/

Comment 1

[Luke Wagner [:luke]]

\o/

Comment 2

[Dan Gohman [:sunfish]]

Attachment: nontrapping.patch

Updated with ARM and x86 support. I'll run some more tests before requesting review.

Comment 3

[Dan Gohman [:sunfish]]

Attachment: nontrapping.patch

Updated with various cleanups. This version takes advantage of the fact that ARM's vcvt performs the desired saturation directly and doesn't need OOL code.

Comment 4

[Nicolas B. Pierron [:nbp]]

Dan, is this blocking any meta bug?

Comment 5

[Dan Gohman [:sunfish]]

It's similar to the sign-ext proposal, which blocks bug 1188259, so I'll do that here too.

Comment 6

[Dan Gohman [:sunfish]]

Attachment: nontrapping.patch

Rebased.

https://treeherder.mozilla.org/#/jobs?repo=try&revision=5550c5aab217420783a901c542bac6ad442b46f7

Comment 7

[Luke Wagner [:luke]]

Comment on attachment 8949481 [details] [diff] [review]
nontrapping.patch

Review of attachment 8949481 [details] [diff] [review]:
-----------------------------------------------------------------

(Sorry for taking so long to review.)  Wow, that was a lot of work, with all the modes in all the backends in all the tiers in all the directions.  Thanks!  Only nits:

::: js/src/jit/MacroAssembler.h
@@ +20,5 @@
> +static const TruncFlags TRUNC_UNSIGNED   = TruncFlags(1) << 0;
> +static const TruncFlags TRUNC_SATURATING = TruncFlags(1) << 1;
> +
> +} // namespace jit
> +} // namespace js

nit: could this hunk be moved into IonTypes.h or some other place?  It seems a bit awkward in the middle of the #includes.

::: js/src/wasm/WasmBaselineCompile.cpp
@@ +7331,5 @@
> +    if (callee == SymbolicAddress::TruncateDoubleToUint64)
> +        flags |= TRUNC_UNSIGNED;
> +    if (callee == SymbolicAddress::SaturatingTruncateDoubleToInt64 ||
> +        callee == SymbolicAddress::SaturatingTruncateDoubleToUint64)
> +        flags |= TRUNC_SATURATING;

nit: { on \n after end of condition and before 'flags |='

::: js/src/wasm/WasmBinaryConstants.h
@@ +332,5 @@
>  
>  inline bool
>  IsPrefixByte(uint8_t b)
>  {
> +    return b >= uint8_t(Op::NumericPrefix);

nit: maybe add an explicit "FirstPrefix" enumerator to Op and use that here?

@@ +337,3 @@
>  }
>  
> +// Opcodes from numeric proposal as of Feb 1, 2018

nit: If the proposal changes or fails to reach the final stage we'll change/remove these, so I think no need to date (dates in comments always look increasingly, well, out-of-date ;) or mention "proposal".

Comment 8

[Dan Gohman [:sunfish]]

Attachment: nontrapping.patch

Review comments addressed. Carrying forward r+.

Comment 9

[Andreea Pavel [:apavel]]

:sunfish the patch failed to apply, could you please provide an updated patch?

Comment 10

[Dan Gohman [:sunfish]]

Attachment: nontrapping.patch

Rebased.

Comment 11

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/mozilla-inbound/rev/25900f3b9936
Implement non-trapping float-to-int conversions for WebAssembly r=luke

Comment 13

[Narcis Beleuzu [:NarcisB]]

https://hg.mozilla.org/mozilla-central/rev/25900f3b9936