cmd/compile: bad line number assigned to instruction

[aarzilli]

Compiling the following with -gcflags='all=-N -l':

package main

type T struct {
	m map[int]int
}

func main() {
	t := T{
		m: make(map[int]int),
	}
	t.Inc(5)
	t.Inc(7)
}

func (s *T) Inc(key int) {
	v := s.m[key] // break, line 16
	v++
	s.m[key] = v // also here
}

Produces a binary for main.(*T).Inc with this:

test.go:16	S	0x45fd3e	8400	TESTB AL, 0(AX)
test.go:16		0x45fd40	488b18	MOVQ 0(AX), BX
test.go:16		0x45fd43	48895c2430	MOVQ BX, 0x30(SP)
test.go:15	S	0x45fd48	488b4c2450	MOVQ 0x50(SP), CX
test.go:16	S	0x45fd4d	488d05cc5c0000	LEAQ main.(*T).Inc+23808(SB), AX
test.go:16		0x45fd54	e8a7f9faff	CALL runtime.mapaccess1_fast64(SB)  >>>

The instruction at 0x45fd48 which passes key to mapaccess1_fast64 is assigned the function's header as its line number instead of the statement it belongs to.

ref. go-delve/delve#3033
cc @dr2chase

[cagedmantis]

/cc @randall77 @griesemer