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7fbb1b36c3
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>
75 lines
1.5 KiB
Go
75 lines
1.5 KiB
Go
// errorcheck -0 -m -l
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// Copyright 2015 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Test escape analysis for function parameters.
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package foo
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var Ssink *string
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type U struct {
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_sp *string
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_spp **string
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}
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func A(sp *string, spp **string) U { // ERROR "leaking param: sp to result ~r2 level=0$" "leaking param: spp to result ~r2 level=0$"
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return U{sp, spp}
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}
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func B(spp **string) U { // ERROR "leaking param: spp to result ~r1 level=0$" "leaking param: spp to result ~r1 level=1$"
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return U{*spp, spp}
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}
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func tA1() {
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s := "cat"
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sp := &s // ERROR "tA1 &s does not escape$"
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spp := &sp // ERROR "tA1 &sp does not escape$"
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u := A(sp, spp)
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_ = u
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println(s)
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}
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func tA2() {
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s := "cat"
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sp := &s // ERROR "tA2 &s does not escape$"
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spp := &sp // ERROR "tA2 &sp does not escape$"
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u := A(sp, spp)
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println(*u._sp)
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}
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func tA3() {
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s := "cat"
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sp := &s // ERROR "tA3 &s does not escape$"
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spp := &sp // ERROR "tA3 &sp does not escape$"
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u := A(sp, spp)
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println(**u._spp)
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}
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func tB1() {
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s := "cat"
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sp := &s // ERROR "tB1 &s does not escape$"
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spp := &sp // ERROR "tB1 &sp does not escape$"
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u := B(spp)
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_ = u
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println(s)
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}
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func tB2() {
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s := "cat"
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sp := &s // ERROR "tB2 &s does not escape$"
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spp := &sp // ERROR "tB2 &sp does not escape$"
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u := B(spp)
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println(*u._sp)
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}
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func tB3() {
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s := "cat"
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sp := &s // ERROR "tB3 &s does not escape$"
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spp := &sp // ERROR "tB3 &sp does not escape$"
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u := B(spp)
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println(**u._spp)
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}
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