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cmd/compile: ignore some dead code during escape analysis 

This is the escape analysis analog of CL 37499.

Fixes #12397
Fixes #16871

The only "moved to heap" decisions eliminated by this
CL in std+cmd are:

cmd/compile/internal/gc/const.go:1514: moved to heap: ac
cmd/compile/internal/gc/const.go:1515: moved to heap: bd
cmd/compile/internal/gc/const.go:1516: moved to heap: bc
cmd/compile/internal/gc/const.go:1517: moved to heap: ad
cmd/compile/internal/gc/const.go:1546: moved to heap: ac
cmd/compile/internal/gc/const.go:1547: moved to heap: bd
cmd/compile/internal/gc/const.go:1548: moved to heap: bc
cmd/compile/internal/gc/const.go:1549: moved to heap: ad
cmd/compile/internal/gc/const.go:1550: moved to heap: cc_plus
cmd/compile/internal/gc/export.go:162: moved to heap: copy
cmd/compile/internal/gc/mpfloat.go:66: moved to heap: b
cmd/compile/internal/gc/mpfloat.go:97: moved to heap: b

Change-Id: I0d420b69c84a41ba9968c394e8957910bab5edea
Reviewed-on: https://go-review.googlesource.com/37508
Reviewed-by: David Chase <drchase@google.com>
This commit is contained in:
Josh Bleecher Snyder 2017-02-27 11:37:54 -08:00
parent 7b8f51188b
commit 1e29cd8c2b
2 changed files with 29 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

19
src/cmd/compile/internal/gc/esc.go
View File

@ -685,11 +685,20 @@ func (e *EscState) esc(n *Node, parent *Node) {
e.escassignSinkWhy(n, n, "too large for stack") // TODO category: tooLarge e.escassignSinkWhy(n, n, "too large for stack") // TODO category: tooLarge
} }
e.esc(n.Left, n) if n.Op == OIF && Isconst(n.Left, CTBOOL) {
e.esc(n.Right, n) // Don't examine dead code.
e.esclist(n.Nbody, n) if n.Left.Bool() {
e.esclist(n.List, n) e.esclist(n.Nbody, n)
e.esclist(n.Rlist, n) } else {
e.esclist(n.Rlist, n)
}
} else {
e.esc(n.Left, n)
e.esc(n.Right, n)
e.esclist(n.Nbody, n)
e.esclist(n.List, n)
e.esclist(n.Rlist, n)
}
if n.Op == OFOR || n.Op == ORANGE { if n.Op == OFOR || n.Op == ORANGE {
e.loopdepth-- e.loopdepth--

15
test/escape2.go
View File

@ -1824,3 +1824,18 @@ func issue11387(x int) func() int {
copy(slice2, slice1) copy(slice2, slice1)
return slice2[0] return slice2[0]
} }
func issue12397(x, y int) { // ERROR "moved to heap: y$"
// x does not escape below, because all relevant code is dead.
if false {
gxx = &x
} else {
gxx = &y // ERROR "&y escapes to heap$"
}
if true {
gxx = &y // ERROR "&y escapes to heap$"
} else {
gxx = &x
}
}