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author | David Chase <drchase@google.com> | 2015-03-26 16:36:15 -0400 |
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committer | David Chase <drchase@google.com> | 2015-05-01 13:47:20 +0000 |
commit | 7fbb1b36c37ac49db78042adc7533fb4ab83a4bc (patch) | |
tree | 053b665f5469d0ba1ad6bf82dd7f4469818bd2d6 /test/escape_array.go | |
parent | 4044adedf7eb8c3ab89f00479965be62e029f350 (diff) | |
download | go-7fbb1b36c37ac49db78042adc7533fb4ab83a4bc.tar.gz go-7fbb1b36c37ac49db78042adc7533fb4ab83a4bc.zip |
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>
Diffstat (limited to 'test/escape_array.go')
-rw-r--r-- | test/escape_array.go | 72 |
1 files changed, 72 insertions, 0 deletions
diff --git a/test/escape_array.go b/test/escape_array.go new file mode 100644 index 0000000000..ac51fe7ca6 --- /dev/null +++ b/test/escape_array.go @@ -0,0 +1,72 @@ +// errorcheck -0 -m -l + +// Copyright 2015 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +// Test escape analysis for function parameters. + +// In this test almost everything is BAD except the simplest cases +// where input directly flows to output. + +package foo + +var Ssink *string + +type U [2]*string + +func bar(a, b *string) U { // ERROR "leaking param: a to result ~r2 level=0$" "leaking param: b to result ~r2 level=0$" + return U{a, b} +} + +func foo(x U) U { // ERROR "leaking param: x to result ~r1 level=0$" + return U{x[1], x[0]} +} + +func bff(a, b *string) U { // ERROR "leaking param: a to result ~r2 level=0$" "leaking param: b to result ~r2 level=0$" + return foo(foo(bar(a, b))) +} + +func tbff1() *string { + a := "cat" + b := "dog" // ERROR "moved to heap: b$" + u := bff(&a, &b) // ERROR "tbff1 &a does not escape$" "tbff1 &b does not escape$" + _ = u[0] + return &b // ERROR "&b escapes to heap$" +} + +// BAD: need fine-grained analysis to track u[0] and u[1] differently. +func tbff2() *string { + a := "cat" // ERROR "moved to heap: a$" + b := "dog" // ERROR "moved to heap: b$" + u := bff(&a, &b) // ERROR "&a escapes to heap$" "&b escapes to heap$" + _ = u[0] + return u[1] +} + +func car(x U) *string { // ERROR "leaking param: x to result ~r1 level=0$" + return x[0] +} + +// BAD: need fine-grained analysis to track x[0] and x[1] differently. +func fun(x U, y *string) *string { // ERROR "leaking param: x to result ~r2 level=0$" "leaking param: y to result ~r2 level=0$" + x[0] = y + return x[1] +} + +func fup(x *U, y *string) *string { // ERROR "leaking param: x to result ~r2 level=1$" "leaking param: y$" + x[0] = y // leaking y to heap is intended + return x[1] +} + +// BAD: would be nice to record that *y (content) is what leaks, not y itself +func fum(x *U, y **string) *string { // ERROR "leaking param: x to result ~r2 level=1$" "leaking param content: y$" + x[0] = *y + return x[1] +} + +// BAD: would be nice to record that y[0] (content) is what leaks, not y itself +func fuo(x *U, y *U) *string { // ERROR "leaking param: x to result ~r2 level=1$" "leaking param content: y$" + x[0] = y[0] + return x[1] +} |