[release-branch.go1.3] cmd/gc: two escape analysis fixes

??? CL 108860043 / f153208c0a0e
cmd/gc: fix escape analysis for &x inside switch x := v.(type)

The analysis for &x was using the loop depth on x set
during x's declaration. A type switch creates a list of
implicit declarations that were not getting initialized
with loop depths.

Fixes issue 8176.

LGTM=iant
R=iant
CC=golang-codereviews
https://codereview.appspot.com/108860043
???

??? CL 108870044 / 331dbd4a6334
cmd/gc: fix &result escaping into result

There is a hierarchy of location defined by loop depth:

        -1 = the heap
        0 = function results
        1 = local variables (and parameters)
        2 = local variable declared inside a loop
        3 = local variable declared inside a loop inside a loop
        etc

In general if an address from loopdepth n is assigned to
something in loop depth m < n, that indicates an extended
lifetime of some form that requires a heap allocation.

Function results can be local variables too, though, and so
they don't actually fit into the hierarchy very well.
Treat the address of a function result as level 1 so that
if it is written back into a result, the address is treated
as escaping.

Fixes  issue 8185 .

LGTM=iant
R=iant
CC=golang-codereviews
https://codereview.appspot.com/108870044
???

LGTM=r
R=golang-codereviews, r
CC=bradfitz, golang-codereviews, iant
https://codereview.appspot.com/107930044

1 files changed, 22 insertions, 0 deletions

diff --git a/test/escape2.go b/test/escape2.go
index 8cb3b6df6..28251aa98 100644
--- a/test/escape2.go
+++ b/test/escape2.go
@@ -1468,3 +1468,25 @@ func foo152() {
 	v := NewV(u)
 	println(v)
 }
+
+// issue 8176 - &x in type switch body not marked as escaping
+
+func foo153(v interface{}) *int { // ERROR "leaking param: v"
+	switch x := v.(type) {
+	case int: // ERROR "moved to heap: x"
+		return &x // ERROR "&x escapes to heap"
+	}
+	panic(0)
+}
+
+// issue 8185 - &result escaping into result
+
+func f() (x int, y *int) { // ERROR "moved to heap: x"
+	y = &x // ERROR "&x escapes to heap"
+	return
+}
+
+func g() (x interface{}) { // ERROR "moved to heap: x"
+	x = &x // ERROR "&x escapes to heap"
+	return
+}