Currently, ion's object allocation and init code will initialize all slots with undefined. In at least one hot path in raytrace (and probably others), this leads to initialization with undefined, immediately followed by the client code re-initializing the slots with the intended values. We should be able to easily detect initialization patterns that cannot bail before all slots have been initialized and elide the allocator's initialization in those cases. In bug 969012, removing a single instruction in this path was worth 3000 on raytrace, so removing 3 more should be a substantial win.

This patch looks for StoreFixedSlot instructions following NewObject/CreateThisWithTemplate etc, and if all fixed slots are initialized we don't initialize the slots to undefined. Incremental GC complicates this a bit, because StoreFixedSlot may have a pre-barrier that looks at the old slot value (garbage if we don't initialize the slots to undefined). This patch is indeed a nice win on Octane-raytrace: at least 7000 points on my machine.

Comment on attachment 8422992 [details] [diff] [review] Patch Review of attachment 8422992 [details] [diff] [review]: ----------------------------------------------------------------- Very nice! r=me ::: js/src/jit/IonMacroAssembler.cpp @@ +750,5 @@ > uint32_t nslots = templateObj->lastProperty()->slotSpan(templateObj->getClass()); > if (nslots == 0) > return; > > uint32_t nfixed = Min(templateObj->numFixedSlots(), nslots); Please make this templateObj->numUsedFixedSlots();

https://hg.mozilla.org/integration/mozilla-inbound/rev/b3f9e15cbfae Green Linux64/Mac Try run: https://tbpl.mozilla.org/?tree=Try&rev=ee4685c4c88a

This doesnt appear to have much effect on octane-raytrace on machine 11 on AWFY... or am i reading it wrong?

(In reply to mayankleoboy1 from comment #5) > This doesnt appear to have much effect on octane-raytrace on machine 11 on > AWFY... or am i reading it wrong? I see about 2000 points on AWFY 32-bit, it's less than what I'm seeing locally, no idea why. I double checked this before I pushed the patch.