[Webkit-unassigned] [Bug 170089] [jsc][mips] Add missing MacroAssembler functions after r214187

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Thu Apr 6 04:01:04 PDT 2017


--- Comment #6 from Adrian Perez <aperez at igalia.com> ---
(In reply to Guillaume Emont from comment #5)

> Another way to put it: the need for special cases for MIPS-I only exists
> when dealing with doubles. The fact of using an ImplicitAddress instead of a
> BaseIndex does not incur this need. 

Oh, I was assuming that loadFloat() would emit a load for a 64-bit value.
Thanks for clarifying.

Then you're right (and I should have checked the code before commenting)
and it's an r+me :-)

> Another debate is whether we still want to support MIPS-I, I don't know if
> there still are many devices using that where it makes sense to use webkit,
> though I could be wrong, because, hey, we have these guards in the code.

The cost of maintaining MIPS-I support is quite low:

  ~/devel/WebKit % rg -F 'WTF_MIPS_ISA(1)' Source | wc -l

There's only the code for emitting load/save of 64-bit floating point values
in “MacroAssemblerMIPS.h”, and two one-liners to insert “nop”-delays after
some load instructions.

It does not seem that it is much of a problem to keep the support around,
though it's difficult to gauge how often JSC ends up running on MIPS-I
hardware. As far as I know that would be only the original R2000/R3000
CPUs, and more recently clones (e.g. OpenCores has a synthetizable clean
room design) often used as microcontrollers — so I have no strong opinion
towards keeping the MIPS-I bits.

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