1656832 - Remove setARMHwCapFlags

Status: RESOLVED FIXED

(Core :: JavaScript Engine: JIT, enhancement, P1)

Description

[Lars T Hansen [:lth]]

We want to:

• remove this function, because it allows "hardware" to have an unstable feature set, and that's evil
• replace it with a shell flag that allows the flags to be set at startup
• gate wasm compilation in HasSupport on ARMv7 explicitly
• update the two test cases that use it with test cases that use the new flag, or kill the tests
• optionally gate Ion on ARMv7 support, if that's not happening already

Comment 1

[Lars T Hansen [:lth]]

Huh, there's already a shell flag, --arm-hwcap. It has been there at least since The Great Reformatting (Nov 2018).

Comment 2

[Lars T Hansen [:lth]]

It is not necessary to gate wasm on ARMv7 explicitly, we gate on various aspects of the hardware, some of which (unaligned accesses) are only supported by ARMv7.

Comment 3

[Lars T Hansen [:lth]]

Attachment: Bug 1656832 - Remove setARMHwCapFlags testing functions. r?bbouvier

This removes the testing function and adjusts the tests that use it.
One test is removed because wasm, and asm.js, are not available
without floating point support (guarded against in HasSupport).

The patch also documents the meaning and logic of the remaining
hardware flag management.

There is already a command line switch for setting the ARM flags (and
an environment variable) so we don't need to introduce anything to
allow flags to be set.

A final adjustment is made to HasSupport: It can call
JitSupportsAtomics() rather than test the ARM flags directly, since
the jit tests those flags on ARM.

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/6ee66102bad0
Remove setARMHwCapFlags testing functions. r=bbouvier

Comment 5

[Cosmin Sabou [:CosminS]]

https://hg.mozilla.org/mozilla-central/rev/6ee66102bad0