1190446 - Add Code Coverage support to Baseline.

Status: RESOLVED FIXED

(Core :: JavaScript Engine: JIT, defect)

Description

[Nicolas B. Pierron [:nbp]]

Currently PCCounts is only in the Interpreter, we should also update the counters in Baseline too, such that we can avoid slowing down the execution by staying in the Interpreter.

Comment 1

[Nicolas B. Pierron [:nbp]]

Attachment: Update Coverage information in Baseline.

This patch updates the numExec counters of the PCCounts, while running in
Baseline.  With the current scheme of updating the numExec counter for each
bytecode, this puts the overhead to 11% of the non-instrumented execution
(on the jsreftest execution).

Comment 2

[Jan de Mooij [:jandem]]

Comment on attachment 8642470 [details] [diff] [review]
Update Coverage information in Baseline.

Review of attachment 8642470 [details] [diff] [review]:
-----------------------------------------------------------------

::: js/src/jit/BaselineCompiler.cpp
@@ +808,5 @@
> +BaselineCompiler::emitCoverage(jsbytecode* pc)
> +{
> +    double* counterAddr = &script->getPCCounts(pc).numExec();
> +    AllocatableRegisterSet regs(RegisterSet::Volatile());
> +    Register counterAddrReg = regs.takeAnyGeneral();

We can keep stack values in R0/R1 between ops, I think using counterAddrReg without saving it could clobber those. Fortunately you can use R2.scratchReg(), it should be available.

@@ +972,5 @@
>          // Emit traps for breakpoints and step mode.
>          if (compileDebugInstrumentation_ && !emitDebugTrap())
>              return Method_Error;
>  
> +        // Emit code coverage code, to fill the same data as the interepreter.

interpreter

@@ +974,5 @@
>              return Method_Error;
>  
> +        // Emit code coverage code, to fill the same data as the interepreter.
> +        if (compileCoverage && !emitCoverage(pc))
> +            return Method_Error;

emitCoverage always returns true so we can just change this to:

if (...)
    emitCoverage();

Comment 3

[Nicolas B. Pierron [:nbp]]

Attachment: Update Coverage information in Baseline.

Side note, the code of emitCovergae is later replaced by an int64 increment, in Bug 1190454.

Comment 4

[Nicolas B. Pierron [:nbp]]

https://treeherder.mozilla.org/#/jobs?repo=try&revision=8ffbb61af473

Comment 5

[Pulsebot]

https://hg.mozilla.org/integration/mozilla-inbound/rev/8b68a9f000b3

Comment 6

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/8b68a9f000b3