1414228 - Allocate type monitor fallback stubs lazily

Status: RESOLVED FIXED

(Core :: JavaScript Engine: JIT, enhancement)

Description

[Jan de Mooij [:jandem]]

Attachment: Patch

Right now we allocate these in BaselineCompiler for ops that are monitored. The attached patch splits fallbackMonitorStub() into maybeFallbackMonitorStub() and getFallbackMonitorStub(), and then we just have to update all callers to use one or the other.

The micro-benchmark below improves from 875 ms to 778 ms (best of 5 runs). Now this is obviously a best case micro-benchmark for this patch, but it's a pretty simple perf and memory usage improvement.

function f() {
    var s = "if (x) return 1;";
    for (var i = 0; i < 2000; i++)
        s += "x = x.foo;";
    var arr = [];
    for (var i = 0; i < 1000; i++)
        arr.push(new Function("x", s));
    var t = new Date;
    for (var i = 0; i < arr.length; i++) {
        for (var j = 0; j < 12; j++)
            arr[i](1);
    }
    print(new Date - t);
}
f();

Comment 1

[Ted Campbell [:tcampbell]]

Comment on attachment 8924927 [details] [diff] [review]
Patch

Review of attachment 8924927 [details] [diff] [review]:
-----------------------------------------------------------------

Great! This patch was hard to follow, but I now see that it was the existing system was confusing and the new code makes way more sense. :)

::: js/src/jit/BaselineBailouts.cpp
@@ +1390,5 @@
>  
>      // Push BaselineStub frame descriptor
>      if (!builder.writeWord(baselineStubFrameDescr, "Descriptor"))
>          return false;
>  

Please add comments to callers of offsetOfFallbackMonitorStub to describe that this code is the corresponding de-lazify. A comment here about the converse.

::: js/src/jit/BaselineIC.h
@@ +430,5 @@
>              hasReceiver_(hasReceiver)
>          { }
>  
>          ICStub* getStub(ICStubSpace* space) {
> +            return newStub<ICGetElem_Fallback>(space, getStubCode());

Nice

::: js/src/jit/SharedIC.h
@@ +1204,1 @@
>      // Pointer to the fallback monitor stub.

Mention that this is lazily created when an optimized stub needing it is added.

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/mozilla-inbound/rev/21fe8fa6b8e6
Allocate type monitor fallback stubs lazily instead of allocating them in BaselineCompiler. r=tcampbell

Comment 3

[Cristina Coroiu [:ccoroiu]]

https://hg.mozilla.org/mozilla-central/rev/21fe8fa6b8e6