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Russ Cox fe3c913443 cmd/gc: fix escape analysis of func returning indirect of parameter 
I introduced this bug when I changed the escape
analysis to run in phases based on call graph
dependency order, in order to be more precise about
inputs escaping back to outputs (functions returning
their arguments).

Given

        func f(z **int) *int { return *z }

we were tagging the function as 'z does not escape
and is not returned', which is all true, but not
enough information.

If used as:

        var x int
        p := &x
        q := &p
        leak(f(q))

then the compiler might try to keep x, p, and q all
on the stack, since (according to the recorded
information) nothing interesting ends up being
passed to leak.

In fact since f returns *q = p, &x is passed to leak
and x needs to be heap allocated.

To trigger the bug, you need a chain that the
compiler wants to keep on the stack (like x, p, q
above), and you need a function that returns an
indirect of its argument, and you need to pass the
head of the chain to that function. This doesn't
come up very often: this bug has been present since
June 2012 (between Go 1 and Go 1.1) and we haven't
seen it until now. It helps that most functions that
return indirects are getters that are simple enough
to be inlined, avoiding the bug.

Earlier versions of Go also had the benefit that if
&x really wasn't used beyond x's lifetime, nothing
broke if you put &x in a heap-allocated structure
accidentally. With the new stack copying, though,
heap-allocated structures containing &x are not
updated when the stack is copied and x moves,
leading to crashes in Go 1.3 that were not crashes
in Go 1.2 or Go 1.1.

The fix is in two parts.

First, in the analysis of a function, recognize when
a value obtained via indirect of a parameter ends up
being returned. Mark those parameters as having
content escape back to the return results (but we
don't bother to write down which result).

Second, when using the analysis to analyze, say,
f(q), mark parameters with content escaping as
having any indirections escape to the heap. (We
don't bother trying to match the content to the
return value.)

The fix could be less precise (simpler).
In the first part we might mark all content-escaping
parameters as plain escaping, and then the second
part could be dropped. Or we might assume that when
calling f(q) all the things pointed at by q escape
always (for any f and q).

The fix could also be more precise (more complex).
We might record the specific mapping from parameter
to result along with the number of indirects from the
parameter to the thing being returned as the result,
and then at the call sites we could set up exactly the
right graph for the called function. That would make
notleaks(f(q)) be able to keep x on the stack, because
the reuslt of f(q) isn't passed to anything that leaks it.

The less precise the fix, the more stack allocations
become heap allocations.

This fix is exactly as precise as it needs to be so that
none of the current stack allocations in the standard
library turn into heap allocations.

Fixes #8120.

LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews, khr, r
https://golang.org/cl/102040046
 		2014-06-03 11:35:59 -04:00
..
bench test/bench/shootout: support windows 2014-05-09 14:34:50 -07:00
bugs cmd/gc: fix wrong interaction between inlining and embedded builtins. 2012-12-22 19:16:31 +01:00
chan test/chan: avoid wrap-around in memstats comparison 2013-09-20 17:27:56 -07:00
ddd2.dir test: convert tests to run.go whenever possible. 2012-10-10 22:35:27 +02:00
dwarf test: make rundir match compiledir/errorcheckdir. 2013-01-11 22:00:48 +01:00
fixedbugs runtime: fix 1-byte return during x.(T) for 0-byte T 2014-06-02 21:06:30 -04:00
import2.dir test: convert more tests to rundir/compiledir conventions 2012-10-07 23:22:01 +02:00
import4.dir test: match gccgo import error messages 2013-12-12 19:02:11 -08:00
interface cmd/gc: don't attempt to generate wrappers for blank interface methods 2013-08-19 11:53:34 +10:00
ken go/test/chan1.go: fix typo 2012-02-25 08:47:04 +11:00
method4.dir cmd/gc: do not omit wrapper for expression (interface{...}).F 2014-01-07 13:26:48 +01:00
safe test: adapt old-style tests to new flag parsing. 2013-01-11 22:05:46 +01:00
stress test/stress: fix a goroutine leak in threadRing stresstest 2013-06-03 07:07:31 -07:00
syntax test: match gccgo error messages 2013-12-12 17:18:12 -08:00
64bit.go cmd/gc: Error out on division by constant zero. 2013-01-30 20:21:08 +01:00
235.go test: [a-c]: add introductory comments to tests 2012-02-19 13:19:43 +11:00
alias.go test: [a-c]: add introductory comments to tests 2012-02-19 13:19:43 +11:00
alias1.go test: ensure all failing tests exit nonzero. 2013-02-12 13:17:49 -05:00
append.go test: [a-c]: add introductory comments to tests 2012-02-19 13:19:43 +11:00
args.go test: run some more tests by default 2012-11-08 09:04:27 -08:00
assign.go test: [a-c]: add introductory comments to tests 2012-02-19 13:19:43 +11:00
assign1.go test: [a-c]: add introductory comments to tests 2012-02-19 13:19:43 +11:00
bigalg.go test: ensure all failing tests exit nonzero. 2013-02-12 13:17:49 -05:00
bigmap.go runtime: handle and test large map values 2012-05-24 22:41:07 -04:00
blank.go test: revert changes made for Go SSA interpreter test. 2013-10-08 14:36:20 -04:00
blank1.go test: match gccgo error messages for blank1.go 2013-09-28 15:19:05 -07:00
bom.go gc: initial BOM is legal. 2012-09-10 13:03:07 -07:00
bombad.go gc: initial BOM is legal. 2012-09-10 13:03:07 -07:00
bounds.go test: prepare for 64-bit ints 2012-09-24 00:06:41 -04:00
chancap.go test: [a-c]: add introductory comments to tests 2012-02-19 13:19:43 +11:00
char_lit.go test: [a-c]: add introductory comments to tests 2012-02-19 13:19:43 +11:00
char_lit1.go test: [a-c]: add introductory comments to tests 2012-02-19 13:19:43 +11:00
closedchan.go
…
closure.go test: enforce 1 proc in the test 2012-07-01 21:59:50 +04:00
cmp.go cmd/gc: do not nop-convert equivalent but different interface types. 2014-02-27 08:07:50 +01:00
cmp6.go cmd/gc: do not consider length zero arrays as comparable. 2014-01-31 00:30:56 +01:00
cmplx.go cmd/gc: reject complex calls with mismatched argument types. 2013-03-11 22:55:14 +01:00
cmplxdivide.c test: use testlib in a few more cases 2012-03-22 02:14:44 +08:00
cmplxdivide.go test: ensure all failing tests exit nonzero. 2013-02-12 13:17:49 -05:00
cmplxdivide1.go test: use testlib in a few more cases 2012-03-22 02:14:44 +08:00
complit.go test: [a-c]: add introductory comments to tests 2012-02-19 13:19:43 +11:00
complit1.go test: [a-c]: add introductory comments to tests 2012-02-19 13:19:43 +11:00
compos.go test: [a-c]: add introductory comments to tests 2012-02-19 13:19:43 +11:00
const.go exp/ssa/interp: (#6 of 5): test interpretation of SSA form of $GOROOT/test/*.go. 2013-02-21 12:48:38 -05:00
const1.go test: match gccgo error messages 2013-12-12 17:18:12 -08:00
const2.go test: match gccgo error messages 2012-09-28 08:30:30 -07:00
const3.go test: [a-c]: add introductory comments to tests 2012-02-19 13:19:43 +11:00
const4.go test: ensure all failing tests exit nonzero. 2013-02-12 13:17:49 -05:00
const5.go cmd/gc: reject builtin function calls in len(fixed array) constants 2014-04-03 19:04:33 -04:00
const6.go test: match gccgo error strings. 2013-06-26 18:05:02 +02:00
convT2X.go cmd/gc: cache itab lookup in convT2I. 2012-07-03 09:09:05 +10:00
convert.go test: [a-c]: add introductory comments to tests 2012-02-19 13:19:43 +11:00
convert1.go test: [a-c]: add introductory comments to tests 2012-02-19 13:19:43 +11:00
convert3.go test: [a-c]: add introductory comments to tests 2012-02-19 13:19:43 +11:00
convlit.go test: [a-c]: add introductory comments to tests 2012-02-19 13:19:43 +11:00
convlit1.go test: [a-c]: add introductory comments to tests 2012-02-19 13:19:43 +11:00
copy.go test: ensure all failing tests exit nonzero. 2013-02-12 13:17:49 -05:00
crlf.go test: use testlib in a few more cases (part 2) 2012-04-20 23:45:43 +08:00
ddd.go test: enable method expression tests in ddd.go 2012-03-07 11:17:26 -08:00
ddd1.go test: match gccgo error messages 2012-09-28 08:30:30 -07:00
ddd2.go test: convert tests to run.go whenever possible. 2012-10-10 22:35:27 +02:00
decl.go test: ensure all failing tests exit nonzero. 2013-02-12 13:17:49 -05:00
declbad.go test: correct type in declbad.go 2012-10-07 21:52:57 +02:00
defer.go test: ensure all failing tests exit nonzero. 2013-02-12 13:17:49 -05:00
deferfin.go runtime: combine small NoScan allocations 2014-01-24 22:35:11 +04:00
deferprint.go test: add cmpout to testlib 2012-02-24 13:17:26 +11:00
deferprint.out
…
divide.go test: ensure all failing tests exit nonzero. 2013-02-12 13:17:49 -05:00
divmod.go all: fix a few spelling errors in source comments 2013-12-27 08:59:02 -08:00
empty.go test: explanatory comments [c-g]* 2012-02-19 14:28:53 +11:00
env.go os: remove Getenverror 2012-02-18 21:18:13 -08:00
eof.go test: explanatory comments [c-g]* 2012-02-19 14:28:53 +11:00
eof1.go test: explanatory comments [c-g]* 2012-02-19 14:28:53 +11:00
errchk test/errchk: use "#!/usr/bin/env perl" shebang line 2013-05-23 04:41:22 +08:00
escape.go test: ensure all failing tests exit nonzero. 2013-02-12 13:17:49 -05:00
escape2.go cmd/gc: fix escape analysis of func returning indirect of parameter 2014-06-03 11:35:59 -04:00
escape3.go test: explanatory comments [c-g]* 2012-02-19 14:28:53 +11:00
escape4.go cmd/gc: fix escape analysis bug 2012-09-24 15:53:12 -04:00
escape5.go cmd/gc: distinguish unnamed vs blank-named return variables better 2014-02-13 20:59:39 -05:00
float_lit.go test: ensure all failing tests exit nonzero. 2013-02-12 13:17:49 -05:00
float_lit2.go test: fix two typos in float_lit2.go 2014-05-21 17:19:12 -04:00
float_lit3.go test/float_lit2.go: rewrite to test values near boundaries 2014-05-21 17:12:06 -04:00
floatcmp.go test: ensure all failing tests exit nonzero. 2013-02-12 13:17:49 -05:00
for.go test: explanatory comments [c-g]* 2012-02-19 14:28:53 +11:00
func.go test: explanatory comments [c-g]* 2012-02-19 14:28:53 +11:00
func1.go cmd/gc: ensure unique parameter and result names in function types 2013-03-15 15:24:13 -04:00
func2.go test: explanatory comments [c-g]* 2012-02-19 14:28:53 +11:00
func3.go test: explanatory comments [c-g]* 2012-02-19 14:28:53 +11:00
func4.go test: explanatory comments [c-g]* 2012-02-19 14:28:53 +11:00
func5.go test: explanatory comments [c-g]* 2012-02-19 14:28:53 +11:00
func6.go test: explanatory comments [c-g]* 2012-02-19 14:28:53 +11:00
func7.go test: ensure all failing tests exit nonzero. 2013-02-12 13:17:49 -05:00
func8.go test: ensure all failing tests exit nonzero. 2013-02-12 13:17:49 -05:00
funcdup.go test: match gccgo error messages 2013-12-12 17:18:12 -08:00
funcdup2.go test: match gccgo error messages 2013-12-12 17:18:12 -08:00
gc.go test: explanatory comments [c-g]* 2012-02-19 14:28:53 +11:00
gc1.go test: explanatory comments [c-g]* 2012-02-19 14:28:53 +11:00
gc2.go build: make nacl pass 2014-05-20 12:10:19 -04:00
gcstring.go runtime: fix empty string handling in garbage collector 2014-03-11 23:58:39 -04:00
golden.out cmd/gc: do not generate code for var _ = ... unless necessary 2012-12-30 12:01:53 -05:00
goprint.go test: make goprint.go wait longer for go its routine to execute 2013-04-12 16:04:19 -07:00
goprint.out
…
goto.go test: explanatory comments [c-g]* 2012-02-19 14:28:53 +11:00
helloworld.go test: add cmpout to testlib 2012-02-24 13:17:26 +11:00
helloworld.out
…
if.go test: commentary for [h-m]*.go 2012-02-23 18:47:26 +11:00
import.go test: commentary for [h-m]*.go 2012-02-23 18:47:26 +11:00
import1.go test: match gccgo import error messages 2013-12-12 19:02:11 -08:00
import2.go test: convert more tests to rundir/compiledir conventions 2012-10-07 23:22:01 +02:00
import4.go test: convert more tests to rundir/compiledir conventions 2012-10-07 23:22:01 +02:00
import5.go gc: disallow absolute import paths 2012-02-29 15:28:36 -05:00
index.go test: recognize gccgo error message in index.go 2013-09-27 20:38:52 -07:00
index0.go test: run index test by default 2012-11-07 12:33:54 -08:00
index1.go test: run index test by default 2012-11-07 12:33:54 -08:00
index2.go test: run index test by default 2012-11-07 12:33:54 -08:00
indirect.go test: commentary for [h-m]*.go 2012-02-23 18:47:26 +11:00
indirect1.go test: commentary for [h-m]*.go 2012-02-23 18:47:26 +11:00
init.go test: commentary for [h-m]*.go 2012-02-23 18:47:26 +11:00
init1.go test: ensure all failing tests exit nonzero. 2013-02-12 13:17:49 -05:00
initcomma.go test/initcomma.go: restore what it's supposed to be testing 2012-02-20 07:44:24 +11:00
initialize.go test: commentary for [h-m]*.go 2012-02-23 18:47:26 +11:00
initializerr.go test: add "duplicate" struct map key test 2012-12-17 11:05:58 -05:00
int_lit.go test: commentary for [h-m]*.go 2012-02-23 18:47:26 +11:00
intcvt.go test: commentary for [h-m]*.go 2012-02-23 18:47:26 +11:00
iota.go test: commentary for [h-m]*.go 2012-02-23 18:47:26 +11:00
label.go test: commentary for [h-m]*.go 2012-02-23 18:47:26 +11:00
label1.go test: commentary for [h-m]*.go 2012-02-23 18:47:26 +11:00
linkx.go test: expand run.go's errorcheck, make clear which bugs run 2012-09-23 13:16:14 -04:00
literal.go test: ensure all failing tests exit nonzero. 2013-02-12 13:17:49 -05:00
live.go cmd/gc: fix liveness for address-taken variables in inlined functions 2014-06-02 21:26:32 -04:00
live1.go cmd/gc: correct liveness for fat variables 2014-02-15 10:58:55 -05:00
live2.go cmd/gc: fix liveness for address-taken variables in inlined functions 2014-06-02 21:26:32 -04:00
mallocfin.go test: commentary for [h-m]*.go 2012-02-23 18:47:26 +11:00
map.go test: fix flaky NaN-key map complexity test 2013-04-07 11:56:15 -07:00
map1.go cmd/gc: fix type checking loop 2012-06-07 03:06:40 -04:00
mapnan.go test/mapnan: use time.Now instead of syscall.Getrusage 2013-10-22 18:33:37 -04:00
method.go test: a number of fixes. 2013-02-11 18:20:52 -05:00
method1.go test: commentary for [h-m]*.go 2012-02-23 18:47:26 +11:00
method2.go cmd/gc: fix method values whose receiver is an unnamed interface. 2013-08-29 10:00:58 +02:00
method3.go test: commentary for [h-m]*.go 2012-02-23 18:47:26 +11:00
method4.go test: convert more tests to rundir/compiledir conventions 2012-10-07 23:22:01 +02:00
method5.go cmd/gc: implement method values 2013-03-20 17:11:09 -04:00
named.go gc: return of ideal bool 2012-02-21 22:54:07 -05:00
named1.go test/[n-z]*.go: add documentation 2012-02-24 11:48:19 +11:00
nil.go test: ensure all failing tests exit nonzero. 2013-02-12 13:17:49 -05:00
nilcheck.go cmd/gc: &x panics if x does 2013-08-15 14:38:32 -04:00
nilptr.go test/nilptr: add more tests 2013-09-05 23:06:34 -04:00
nilptr2.go test: revert changes made for Go SSA interpreter test. 2013-10-08 14:36:20 -04:00
nilptr3.go cmd/gc: correct handling of globals, func args, results 2014-05-15 15:34:53 -04:00
nilptr4.go cmd/gc: fix bad checknil with ints on 32 bit compilers 2014-02-26 12:25:13 -08:00
nosplit.go build: make nacl pass 2014-05-20 12:10:19 -04:00
nul1.go test: run some more tests by default 2012-11-08 09:04:27 -08:00
parentype.go test/[n-r]*.go: add documentation 2012-02-24 10:30:39 +11:00
peano.go test/[n-r]*.go: add documentation 2012-02-24 10:30:39 +11:00
printbig.go test: add cmpout to testlib 2012-02-24 13:17:26 +11:00
printbig.out
…
range.go test: a number of fixes. 2013-02-11 18:20:52 -05:00
recover.go test: disable failing tests under ssa/interp. 2013-09-18 14:44:57 -04:00
recover1.go test: use testlib (final 61) 2012-02-16 23:51:04 -05:00
recover2.go test: use testlib (final 61) 2012-02-16 23:51:04 -05:00
recover3.go tests: remove two misuses of nil pointers 2013-08-15 11:51:04 -04:00
rename.go test: ensure all failing tests exit nonzero. 2013-02-12 13:17:49 -05:00
rename1.go test: fix the fix of the rename tests. 2012-02-24 15:06:32 +11:00
reorder.go test: a number of fixes. 2013-02-11 18:20:52 -05:00
reorder2.go cmd/gc: shorten temporary lifetimes when possible 2014-04-01 13:31:38 -04:00
return.go test: add cases to return.go that gccgo got wrong 2013-08-07 11:31:01 -07:00
rotate.go test: add rotate.go and fixedbugs/bug313 2013-01-11 22:42:55 +01:00
rotate0.go test: add rotate.go and fixedbugs/bug313 2013-01-11 22:42:55 +01:00
rotate1.go test: add rotate.go and fixedbugs/bug313 2013-01-11 22:42:55 +01:00
rotate2.go test: add rotate.go and fixedbugs/bug313 2013-01-11 22:42:55 +01:00
rotate3.go test: add rotate.go and fixedbugs/bug313 2013-01-11 22:42:55 +01:00
run test/run: add /usr/pkg/bin to PATH. 2014-03-03 02:16:15 -05:00
run.go test/run: limit parallelism to 1 for cross-exec builds 2014-05-28 01:01:08 -04:00
rune.go test/[n-r]*.go: add documentation 2012-02-24 10:30:39 +11:00
runtime.go test/[n-r]*.go: add documentation 2012-02-24 10:30:39 +11:00
shift1.go test/shift1.go: recognize gccgo errors 2013-06-26 08:23:52 -07:00
shift2.go test: add shift expression incorrectly rejected by gccgo. 2013-06-25 08:06:34 +02:00
sieve.go test/[n-z]*.go: add documentation 2012-02-24 11:48:19 +11:00
sigchld.go test: skip SIGCHLD test on Plan 9 2014-01-29 09:28:23 +01:00
sigchld.out
…
simassign.go test/[n-z]*.go: add documentation 2012-02-24 11:48:19 +11:00
sinit.go cmd/gc: do not generate code for var _ = ... unless necessary 2012-12-30 12:01:53 -05:00
sizeof.go test: correct sizeof.go. 2013-06-02 19:10:11 +02:00
slice3.go cmd/gc: support x[i:j:k] 2013-07-01 20:32:36 -04:00
slice3err.go test: match gccgo error messages 2013-12-12 17:18:12 -08:00
solitaire.go test/[n-z]*.go: add documentation 2012-02-24 11:48:19 +11:00
stack.go test/[n-z]*.go: add documentation 2012-02-24 11:48:19 +11:00
string_lit.go test: add []rune case to string_lit.go 2013-12-12 17:17:02 -08:00
stringrange.go all: make Unicode surrogate halves illegal as UTF-8 2012-08-08 14:01:23 -07:00
struct0.go test/[n-z]*.go: add documentation 2012-02-24 11:48:19 +11:00
switch.go cmd/gc: disallow fallthrough in final case of switch 2013-03-15 00:35:09 -04:00
switch3.go cmd/gc: accept switches on comparable arrays. 2012-08-03 21:47:26 +02:00
switch4.go cmd/gc: disallow fallthrough in final case of switch 2013-03-15 00:35:09 -04:00
testlib test/run: process build tags like go/build 2013-08-13 12:25:41 -04:00
tinyfin.go runtime: combine small NoScan allocations 2014-01-24 22:35:11 +04:00
torture.go cmd/8g: introduce temporaries in byte multiplication. 2012-12-21 23:46:16 +01:00
turing.go test/[n-z]*.go: add documentation 2012-02-24 11:48:19 +11:00
typecheck.go cmd/gc: silence assignment errors to undefined symbols 2014-01-03 21:03:20 +01:00
typeswitch.go test/[n-z]*.go: add documentation 2012-02-24 11:48:19 +11:00
typeswitch1.go test/[n-z]*.go: add documentation 2012-02-24 11:48:19 +11:00
typeswitch2.go test/[n-z]*.go: add documentation 2012-02-24 11:48:19 +11:00
typeswitch3.go test: match gccgo error messages 2012-09-28 08:30:30 -07:00
undef.go test/[n-z]*.go: add documentation 2012-02-24 11:48:19 +11:00
utf.go test/[n-z]*.go: add documentation 2012-02-24 11:48:19 +11:00
varerr.go test/[n-z]*.go: add documentation 2012-02-24 11:48:19 +11:00
varinit.go test/[n-z]*.go: add documentation 2012-02-24 11:48:19 +11:00
zerodivide.go test: ensure all failing tests exit nonzero. 2013-02-12 13:17:49 -05:00