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>

1 files changed, 57 insertions, 30 deletions

diff --git a/test/escape_param.go b/test/escape_param.go
index 91ad437d86..cfbcd51ca7 100644
--- a/test/escape_param.go
+++ b/test/escape_param.go
@@ -14,7 +14,7 @@ package escape
 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 @@ func caller0b() {
 }
 
 // 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 @@ type Pair struct {
 	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 @@ func caller5() {
 }
 
 // *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 @@ func caller8() {
 }
 
 // *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 @@ func caller9b() {
 }
 
 // **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 @@ func caller11b() {
 	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 @@ func caller13h() {
 	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)
+}