Long-running compilation steps

[Nicholas Nethercote]

Hi,

For https://bugzilla.mozilla.org/show_bug.cgi?id=842800 I'm interested
in adding more checks of SpiderMonkey's operation callback in
potentially long-running operations. For example, when running the
asm.js Unreal demo, parsing takes several seconds, so in my patch I
added a check after the parsing of each statement.

I'm also seeing that IonMonkey compilation can take a while on the
demo. Is there a loop or loops in IonMonkey that are good candidates
for adding operation callback checks?

Nick

[Nicolas B. Pierron]

IonMonkey compilation is currently sequential for the IonBuilder phase and
the CodeGenerator::link phase. All the rest might run in a separate thread
(or not in case of mono core architectures).

Before the compilation we allocate a lifo-alloc which got extend if needed
by the compilation. As far as I know, everything which goes into the
lifo-alloc is considered as dark-matter from the about:memory point of view.

I am not sure what you are trying to look at but what might be interesting
would be to look at the usage of the lifo alloc. It would be safe to do it
at the creation of each basic block, and in MIRGenerator::shouldCancel
(called at each loop iteration on basic blocks) if it is safe to report such
status from another thread.

--
Nicolas B. Pierron

[David Anderson]

IonBuilder::traverseBytecode() should probably have an operation
callback check.

-David

[Luke Wagner]

There are also a bunch of phases in backend codegen that take a bunch of time. (To wit, IonBuilder doesn't run for OdinMonkey.) From profiling asm.js, phi-removal and register allocation are the expensive phases. Unfortunately, each compilation step has it's own driving loop. I think one nice pinch point (that is checked between each phases) is MIRGenerator::shouldCancel; the name even lines up.

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[Brian Hackett]

MIRGenerator::shouldCancel is actually checked all over the place within
phases too, and is, yeah, the trigger to use for canceling off thread
compilations from a different thread.

Brian