cmd/internal/gc: improve flow of input params to output params
This includes the following information in the per-function summary:
outK = paramJ encoded in outK bits for paramJ
outK = *paramJ encoded in outK bits for paramJ
heap = paramJ EscHeap
heap = *paramJ EscContentEscapes
Note that (currently) if the address of a parameter is taken and
returned, necessarily a heap allocation occurred to contain that
reference, and the heap can never refer to stack, therefore the
parameter and everything downstream from it escapes to the heap.
The per-function summary information now has a tuneable number of bits
(2 is probably noticeably better than 1, 3 is likely overkill, but it
is now easy to check and the -m debugging output includes information
that allows you to figure out if more would be better.)
A new test was added to check pointer flow through struct-typed and
*struct-typed parameters and returns; some of these are sensitive to
the number of summary bits, and ought to yield better results with a
more competent escape analysis algorithm. Another new test checks
(some) correctness with array parameters, results, and operations.
The old analysis inferred a piece of plan9 runtime was non-escaping by
counteracting overconservative analysis with buggy analysis; with the
bug fixed, the result was too conservative (and it's not easy to fix
in this framework) so the source code was tweaked to get the desired
result. A test was added against the discovered bug.
The escape analysis was further improved splitting the "level" into
3 parts, one tracking the conventional "level" and the other two
computing the highest-level-suffix-from-copy, which is used to
generally model the cancelling effect of indirection applied to
address-of.
With the improved escape analysis enabled, it was necessary to
modify one of the runtime tests because it now attempts to allocate
too much on the (small, fixed-size) G0 (system) stack and this
failed the test.
Compiling src/std after touching src/runtime/*.go with -m logging
turned on shows 420 fewer heap allocation sites (10538 vs 10968).
Profiling allocations in src/html/template with
for i in {1..5} ;
do go tool 6g -memprofile=mastx.${i}.prof -memprofilerate=1 *.go;
go tool pprof -alloc_objects -text mastx.${i}.prof ;
done
showed a 15% reduction in allocations performed by the compiler.
Update #3753
Update #4720
Fixes #10466
Change-Id: I0fd97d5f5ac527b45f49e2218d158a6e89951432
Reviewed-on: https://go-review.googlesource.com/8202
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
diff --git a/test/escape_param.go b/test/escape_param.go
index 91ad437..cfbcd51 100644
--- a/test/escape_param.go
+++ b/test/escape_param.go
@@ -14,7 +14,7 @@
var sink interface{}
// in -> out
-func param0(p *int) *int { // ERROR "leaking param: p to result ~r1$"
+func param0(p *int) *int { // ERROR "leaking param: p to result ~r1"
return p
}
@@ -29,7 +29,7 @@
}
// in, in -> out, out
-func param1(p1, p2 *int) (*int, *int) { // ERROR "leaking param: p1 to result ~r2$" "leaking param: p2 to result ~r3$"
+func param1(p1, p2 *int) (*int, *int) { // ERROR "leaking param: p1 to result ~r2" "leaking param: p2 to result ~r3"
return p1, p2
}
@@ -64,23 +64,23 @@
p2 *int
}
-func param3(p *Pair) { // ERROR "leaking param: p$"
+func param3(p *Pair) { // ERROR "leaking param content: p$"
p.p1 = p.p2
}
func caller3a() {
i := 0 // ERROR "moved to heap: i$"
j := 0 // ERROR "moved to heap: j$"
- p := Pair{&i, &j} // ERROR "&i escapes to heap$" "&j escapes to heap$" "moved to heap: p$"
- param3(&p) // ERROR "&p escapes to heap$"
+ p := Pair{&i, &j} // ERROR "&i escapes to heap$" "&j escapes to heap$"
+ param3(&p) // ERROR "caller3a &p does not escape"
_ = p
}
func caller3b() {
i := 0 // ERROR "moved to heap: i$"
j := 0 // ERROR "moved to heap: j$"
- p := Pair{&i, &j} // ERROR "&i escapes to heap$" "&j escapes to heap$" "moved to heap: p$"
- param3(&p) // ERROR "&p escapes to heap$"
+ p := Pair{&i, &j} // ERROR "&i escapes to heap$" "&j escapes to heap$"
+ param3(&p) // ERROR "caller3b &p does not escape"
sink = p // ERROR "p escapes to heap$"
}
@@ -114,27 +114,27 @@
}
// *in -> heap
-func param6(i ***int) { // ERROR "leaking param: i$"
+func param6(i ***int) { // ERROR "leaking param content: i$"
sink = *i // ERROR "\*i escapes to heap$"
}
func caller6a() {
i := 0 // ERROR "moved to heap: i$"
p := &i // ERROR "&i escapes to heap$" "moved to heap: p$"
- p2 := &p // ERROR "&p escapes to heap$" "moved to heap: p2$"
- param6(&p2) // ERROR "&p2 escapes to heap$"
+ p2 := &p // ERROR "&p escapes to heap$"
+ param6(&p2) // ERROR "caller6a &p2 does not escape"
}
// **in -> heap
-func param7(i ***int) { // ERROR "leaking param: i$"
+func param7(i ***int) { // ERROR "leaking param content: i$"
sink = **i // ERROR "\* \(\*i\) escapes to heap"
}
func caller7() {
i := 0 // ERROR "moved to heap: i$"
p := &i // ERROR "&i escapes to heap$" "moved to heap: p$"
- p2 := &p // ERROR "&p escapes to heap$" "moved to heap: p2$"
- param7(&p2) // ERROR "&p2 escapes to heap$"
+ p2 := &p // ERROR "&p escapes to heap$"
+ param7(&p2) // ERROR "caller7 &p2 does not escape"
}
// **in -> heap
@@ -149,14 +149,14 @@
}
// *in -> out
-func param9(p ***int) **int { // ERROR "param9 leaking param p content to result ~r1$"
+func param9(p ***int) **int { // ERROR "leaking param: p to result ~r1 level=1"
return *p
}
func caller9a() {
- i := 0 // ERROR "moved to heap: i$"
- p := &i // ERROR "&i escapes to heap$" "moved to heap: p$"
- p2 := &p // ERROR "&p escapes to heap$"
+ i := 0
+ p := &i // ERROR "caller9a &i does not escape"
+ p2 := &p // ERROR "caller9a &p does not escape"
_ = param9(&p2) // ERROR "caller9a &p2 does not escape$"
}
@@ -168,33 +168,33 @@
}
// **in -> out
-func param10(p ***int) *int { // ERROR "param10 leaking param p content to result ~r1$"
+func param10(p ***int) *int { // ERROR "leaking param: p to result ~r1 level=2"
return **p
}
func caller10a() {
- i := 0 // ERROR "moved to heap: i$"
- p := &i // ERROR "&i escapes to heap$" "moved to heap: p$"
- p2 := &p // ERROR "&p escapes to heap$"
+ i := 0
+ p := &i // ERROR "caller10a &i does not escape"
+ p2 := &p // ERROR "caller10a &p does not escape"
_ = param10(&p2) // ERROR "caller10a &p2 does not escape$"
}
func caller10b() {
i := 0 // ERROR "moved to heap: i$"
- p := &i // ERROR "&i escapes to heap$" "moved to heap: p$"
- p2 := &p // ERROR "&p escapes to heap$"
+ p := &i // ERROR "&i escapes to heap$"
+ p2 := &p // ERROR "caller10b &p does not escape$"
sink = param10(&p2) // ERROR "caller10b &p2 does not escape$" "param10\(&p2\) escapes to heap"
}
-// &in -> out
+// in escapes to heap (address of param taken and returned)
func param11(i **int) ***int { // ERROR "moved to heap: i$"
return &i // ERROR "&i escapes to heap$"
}
func caller11a() {
- i := 0 // ERROR "moved to heap: i$"
- p := &i // ERROR "&i escapes to heap$" "moved to heap: p$"
- _ = param11(&p) // ERROR "&p escapes to heap$"
+ i := 0 // ERROR "moved to heap: i"
+ p := &i // ERROR "moved to heap: p" "&i escapes to heap"
+ _ = param11(&p) // ERROR "&p escapes to heap"
}
func caller11b() {
@@ -203,10 +203,17 @@
sink = param11(&p) // ERROR "&p escapes to heap$" "param11\(&p\) escapes to heap"
}
-func caller11c() {
+func caller11c() { // GOOD
i := 0 // ERROR "moved to heap: i$"
- p := &i // ERROR "&i escapes to heap$" "moved to heap: p$"
- sink = *param11(&p) // ERROR "&p escapes to heap$" "\*param11\(&p\) escapes to heap"
+ p := &i // ERROR "moved to heap: p" "&i escapes to heap"
+ sink = *param11(&p) // ERROR "&p escapes to heap" "\*param11\(&p\) escapes to heap"
+}
+
+func caller11d() {
+ i := 0 // ERROR "moved to heap: i$"
+ p := &i // ERROR "&i escapes to heap" "moved to heap: p"
+ p2 := &p // ERROR "&p escapes to heap"
+ sink = param11(p2) // ERROR "param11\(p2\) escapes to heap"
}
// &in -> rcvr
@@ -324,3 +331,23 @@
v.param13(&i) // ERROR "&i escapes to heap$"
sink = **v.p // ERROR "\* \(\*v\.p\) escapes to heap"
}
+
+type Node struct {
+ p *Node
+}
+
+var Sink *Node
+
+func f(x *Node) { // ERROR "leaking param content: x"
+ Sink = &Node{x.p} // ERROR "&Node literal escapes to heap"
+}
+
+func g(x *Node) *Node { // ERROR "leaking param: x to result ~r1 level=0"
+ return &Node{x.p} // ERROR "&Node literal escapes to heap"
+}
+
+func h(x *Node) { // ERROR "leaking param: x"
+ y := &Node{x} // ERROR "h &Node literal does not escape"
+ Sink = g(y)
+ f(y)
+}
