1799919 - V128::extractLane converts NaN to qNaN on x86 32-bit platforms.

Status: RESOLVED FIXED

(Core :: JavaScript: WebAssembly, defect)

Description

[Yury Delendik (:yury)]

We have:

template <typename T>
  T extractLane(unsigned char *bytes, unsigned lane) {
    T result;
    memcpy(&result, bytes + sizeof(T) * lane, sizeof(T));
    return result;
  }

float user( unsigned char *s) { return extractLane<float>(s, 0);}

And on X86 it produces:

  movl 4(%esp), %eax
  flds (%eax)
  retl

vs on X64:

  movss (%rdi), %xmm0
  retq

The flds converts stuff to qNaNs, which we don't expect in wasm world.

Comment 1

[Yury Delendik (:yury)]

Attachment: Bug 1799919 - Refactor V128::extractLane to avoid FLDS on X86. r?jseward

The same logic, but it avoid generation of FLDS instruction at
low level.

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/c12c629265d0
Refactor V128::extractLane to avoid FLDS on X86. r=jseward

Comment 3

[Norisz Fay [:noriszfay]]

https://hg.mozilla.org/mozilla-central/rev/c12c629265d0

Comment 4

[Norisz Fay [:noriszfay]]

https://hg.mozilla.org/mozilla-central/rev/c12c629265d0