825892 - rm JSOP_LOOKUPSWITCH

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Jan de Mooij [:jandem]]

Compiling LOOKUPSWITCH is complicated, and this op hurts JIT performance more than it helps:

* IonMonkey compiles LOOKUPSWITCH and CONDSWITCH to the same MIR. Handling these ops adds a lot of complexity to IonBuilder.

* JM(+TI) always stubs LOOKUPSWITCH and usually spends a lot of time in FindNativeCode. Without LOOKUPSWITCH we'd use CONDSWITCH/CASE/DEFAULT and in many cases these are faster because they can avoid stub calls.

* Efficiently compiling LOOKUPSWITCH in the new baseline compiler is also not trivial, especially compared to CONDSWITCH/CASE which can just use the existing equality IC.

Comment 1

[Jan de Mooij [:jandem]]

Attachment: Remove JSOP_LOOKUPSWITCH

18 files changed, 68 insertions(+), 722 deletions(-)

Comment 2

[Brian Hackett [Laid off!]]

Comment on attachment 697110 [details] [diff] [review]
Remove JSOP_LOOKUPSWITCH

Review of attachment 697110 [details] [diff] [review]:
-----------------------------------------------------------------

Nice!

Comment 3

[Jan de Mooij [:jandem]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/c0e7cc40f356

Try: https://tbpl.mozilla.org/?tree=Try&rev=4c8bc694ada0

Comment 4

[Ed Morley [:emorley]]

https://hg.mozilla.org/mozilla-central/rev/c0e7cc40f356