feat: cpu profile

[zhuliquan]

This is proof of concept PR, which help to analyze expr profile. I notice that expr has profile feature, but Config doesn't explode it for user (i.e. user can't set Profile true).

expr/compiler/compiler.go

Lines 212 to 232 in 80f0ea6

	if c.config != nil && c.config.Profile {
	span := &Span{
	Name: reflect.TypeOf(node).String(),
	Expression: node.String(),
	}
	if len(c.spans) > 0 {
	prev := c.spans[len(c.spans)-1]
	prev.Children = append(prev.Children, span)
	}
	c.spans = append(c.spans, span)
	defer func() {
	if len(c.spans) > 1 {
	c.spans = c.spans[:len(c.spans)-1]
	}
	}()
	c.emit(OpProfileStart, c.addConstant(span))
	defer func() {
	c.emit(OpProfileEnd, c.addConstant(span))
	}()
	}

I think it's very likely that the reason lies in how you show the profile results. I've noticed that the results are saved to a structure called Span.

expr/vm/utils.go

Lines 27 to 33 in 80f0ea6

	type Span struct {
	Name string `json:"name"`
	Expression string `json:"expression"`
	Duration int64 `json:"duration"`
	Children []*Span `json:"children"`
	start time.Time
	}

My idea is to convert the information stored in the Span result into a pprof file, so that we can use go tool pprof command to visualise how the expression is running and find out where it is time-consuming.

I create new sub-module profile. I write a function GeneratePprofProfile to convert Span struct to pprof file (Of course, this function is not perfect, and the profile may need to be more refined. Profile construct). Finally I write a example code and got below result.