devirtualize

Documentation

Overview

Package devirtualize implements two "devirtualization" optimization passes:

• "Static" devirtualization which replaces interface method calls with direct concrete-type method calls where possible.
• "Profile-guided" devirtualization which replaces indirect calls with a conditional direct call to the hottest concrete callee from a profile, as well as a fallback using the original indirect call.

Index

• func ProfileGuided(fn *ir.Func, p *pgo.Profile)
• func StaticCall(call *ir.CallExpr)
• type CallStat

Functions

func ProfileGuided

func ProfileGuided(fn *ir.Func, p *pgo.Profile)

ProfileGuided performs call devirtualization of indirect calls based on profile information.

Specifically, it performs conditional devirtualization of interface calls or function value calls for the hottest callee.

That is, for interface calls it performs a transformation like:

type Iface interface {
	Foo()
}

type Concrete struct{}

func (Concrete) Foo() {}

func foo(i Iface) {
	i.Foo()
}

to:

func foo(i Iface) {
	if c, ok := i.(Concrete); ok {
		c.Foo()
	} else {
		i.Foo()
	}
}

For function value calls it performs a transformation like:

func Concrete() {}

func foo(fn func()) {
	fn()
}

to:

func foo(fn func()) {
	if internal/abi.FuncPCABIInternal(fn) == internal/abi.FuncPCABIInternal(Concrete) {
		Concrete()
	} else {
		fn()
	}
}

The primary benefit of this transformation is enabling inlining of the direct call.

func StaticCall

func StaticCall(call *ir.CallExpr)

StaticCall devirtualizes the given call if possible when the concrete callee is available statically.

Types

type CallStat

type CallStat struct {
	Pkg string // base.Ctxt.Pkgpath
	Pos string // file:line:col of call.

	Caller string // Linker symbol name of calling function.

	// Direct or indirect call.
	Direct bool

	// For indirect calls, interface call or other indirect function call.
	Interface bool

	// Total edge weight from this call site.
	Weight int64

	// Hottest callee from this call site, regardless of type
	// compatibility.
	Hottest       string
	HottestWeight int64

	// Devirtualized callee if != "".
	//
	// Note that this may be different than Hottest because we apply
	// type-check restrictions, which helps distinguish multiple calls on
	// the same line.
	Devirtualized       string
	DevirtualizedWeight int64
}

CallStat summarizes a single call site.

This is used only for debug logging.