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_indir.go b/test/escape_indir.go
index 7c06ceb..fe03c3f 100644
--- a/test/escape_indir.go
+++ b/test/escape_indir.go
@@ -54,14 +54,14 @@
i := 0 // ERROR "moved to heap: i"
x := &ConstPtr{} // ERROR "&ConstPtr literal escapes to heap"
x.p = &i // ERROR "&i escapes to heap"
- sink = x // ERROR "x escapes to heap"
+ sink = x // ERROR "x escapes to heap"
}
func constptr2() {
i := 0 // ERROR "moved to heap: i"
x := &ConstPtr{} // ERROR "&ConstPtr literal does not escape"
x.p = &i // ERROR "&i escapes to heap"
- sink = *x// ERROR "\*x escapes to heap"
+ sink = *x // ERROR "\*x escapes to heap"
}
func constptr4() *ConstPtr {
@@ -78,7 +78,7 @@
}
// BAD: p should not escape here
-func constptr6(p *ConstPtr) { // ERROR "leaking param: p"
+func constptr6(p *ConstPtr) { // ERROR "leaking param content: p"
p1 := &ConstPtr{} // ERROR "&ConstPtr literal does not escape"
*p1 = *p
_ = p1
@@ -151,3 +151,10 @@
i := 0 // ERROR "moved to heap: i"
*p = &i // ERROR "&i escapes to heap"
}
+
+var global *byte
+
+func f() {
+ var x byte // ERROR "moved to heap: x"
+ global = &*&x // ERROR "&\(\*\(&x\)\) escapes to heap" "&x escapes to heap"
+}
