In hairVisitor.doNode we give calls a cost of 57, unless the call is inlineable, in which case we use the cost of the callee, under the assumption that this call will get inlined.
"Inlineable" here more-or-less just means that fn.Inl != nil. In a non-PGO build, we only set fn.Inl if the function cost is < 80, making it inlineable ~anywhere.
In a PGO build, fn.Inl is set for any function involved in a hot callsite (e.g., a -> b), but we will only inline at the hot callsite. Any other callsite (e.g., c -> b) will not inline. This makes the assumption incorrect and means that the cold caller (c) will have an artificially inflated cost, potentially making it too expensive to inline.
I will send a CL to fix this.
cc @cherrymui @thanm @mdempsky
In
hairVisitor.doNodewe give calls a cost of 57, unless the call is inlineable, in which case we use the cost of the callee, under the assumption that this call will get inlined."Inlineable" here more-or-less just means that
fn.Inl != nil. In a non-PGO build, we only setfn.Inlif the function cost is < 80, making it inlineable ~anywhere.In a PGO build,
fn.Inlis set for any function involved in a hot callsite (e.g.,a->b), but we will only inline at the hot callsite. Any other callsite (e.g.,c->b) will not inline. This makes the assumption incorrect and means that the cold caller (c) will have an artificially inflated cost, potentially making it too expensive to inline.I will send a CL to fix this.
cc @cherrymui @thanm @mdempsky