There is a hierarchy of location defined by loop depth:
-1 = the heap
0 = function results
1 = local variables (and parameters)
2 = local variable declared inside a loop
3 = local variable declared inside a loop inside a loop
etc
In general if an address from loopdepth n is assigned to
something in loop depth m < n, that indicates an extended
lifetime of some form that requires a heap allocation.
Function results can be local variables too, though, and so
they don't actually fit into the hierarchy very well.
Treat the address of a function result as level 1 so that
if it is written back into a result, the address is treated
as escaping.
Fixes#8185.
LGTM=iant
R=iant
CC=golang-codereviews
https://golang.org/cl/108870044
The analysis for &x was using the loop depth on x set
during x's declaration. A type switch creates a list of
implicit declarations that were not getting initialized
with loop depths.
Fixes#8176.
LGTM=iant
R=iant
CC=golang-codereviews
https://golang.org/cl/108860043
A runtime.Goexit during a panic-invoked deferred call
left the panic stack intact even though all the stack frames
are gone when the goroutine is torn down.
The next goroutine to reuse that struct will have a
bogus panic stack and can cause the traceback routines
to walk into garbage.
Most likely to happen during tests, because t.Fatal might
be called during a deferred func and uses runtime.Goexit.
This "not enough cleared in Goexit" failure mode has
happened to us multiple times now. Clear all the pointers
that don't make sense to keep, not just gp->panic.
Fixes#8158.
LGTM=iant, dvyukov
R=iant, dvyukov
CC=golang-codereviews
https://golang.org/cl/102220043
I am not sure what the rounding here was
trying to do, but it was skipping the first
pointer on native client.
The code above the rounding already checks
that xoffset is widthptr-aligned, so the rnd
was a no-op everywhere but on Native Client.
And on Native Client it was wrong.
Perhaps it was supposed to be rounding down,
not up, but zerorange handles the extra 32 bits
correctly, so the rnd does not seem to be necessary
at all.
This wouldn't be worth doing for Go 1.3 except
that it can affect code on the playground.
Fixes#8155.
LGTM=r, iant
R=golang-codereviews, r, iant
CC=dvyukov, golang-codereviews, khr
https://golang.org/cl/108740047
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
The 'address taken' bit in a function variable was not
propagating into the inlined copies, causing incorrect
liveness information.
LGTM=dsymonds, bradfitz
R=golang-codereviews, bradfitz
CC=dsymonds, golang-codereviews, iant, khr, r
https://golang.org/cl/96670046
The 1-byte write was silently clearing a byte on the stack.
If there was another function call with more arguments
in the same stack frame, no harm done.
Otherwise, if the variable at that location was already zero,
no harm done.
Otherwise, problems.
Fixes#8139.
LGTM=dsymonds
R=golang-codereviews, dsymonds
CC=golang-codereviews, iant, r
https://golang.org/cl/100940043
We were requiring that the defer stack and the panic stack
be completely processed, thinking that if any were left over
the stack scan and the defer stack/panic stack must be out
of sync. It turns out that the panic stack may well have
leftover entries in some situations, and that's okay.
Fixes#8132.
LGTM=minux, r
R=golang-codereviews, minux, r
CC=golang-codereviews, iant, khr
https://golang.org/cl/100900044
The 'continuation pc' is where the frame will continue
execution, if anywhere. For a frame that stopped execution
due to a CALL instruction, the continuation pc is immediately
after the CALL. But for a frame that stopped execution due to
a fault, the continuation pc is the pc after the most recent CALL
to deferproc in that frame, or else 0. That is where execution
will continue, if anywhere.
The liveness information is only recorded for CALL instructions.
This change makes sure that we never look for liveness information
except for CALL instructions.
Using a valid PC fixes crashes when a garbage collection or
stack copying tries to process a stack frame that has faulted.
Record continuation pc in heapdump (format change).
Fixes#8048.
LGTM=iant, khr
R=khr, iant, dvyukov
CC=golang-codereviews, r
https://golang.org/cl/100870044
This CL forces the optimizer to preserve some memory stores
that would be redundant except that a stack scan due to garbage
collection or stack copying might look at them during a function call.
As such, it forces additional memory writes and therefore slows
down the execution of some programs, especially garbage-heavy
programs that are already limited by memory bandwidth.
The slowdown can be as much as 7% for end-to-end benchmarks.
These numbers are from running go1.test -test.benchtime=5s three times,
taking the best (lowest) ns/op for each benchmark. I am excluding
benchmarks with time/op < 10us to focus on macro effects.
All benchmarks are on amd64.
Comparing tip (a27f34c771cb) against this CL on an Intel Core i5 MacBook Pro:
benchmark old ns/op new ns/op delta
BenchmarkBinaryTree17 3876500413 3856337341 -0.52%
BenchmarkFannkuch11 2965104777 2991182127 +0.88%
BenchmarkGobDecode 8563026 8788340 +2.63%
BenchmarkGobEncode 5050608 5267394 +4.29%
BenchmarkGzip 431191816 434168065 +0.69%
BenchmarkGunzip 107873523 110563792 +2.49%
BenchmarkHTTPClientServer 85036 86131 +1.29%
BenchmarkJSONEncode 22143764 22501647 +1.62%
BenchmarkJSONDecode 79646916 85658808 +7.55%
BenchmarkMandelbrot200 4720421 4700108 -0.43%
BenchmarkGoParse 4651575 4712247 +1.30%
BenchmarkRegexpMatchMedium_1K 71986 73490 +2.09%
BenchmarkRegexpMatchHard_1K 111018 117495 +5.83%
BenchmarkRevcomp 648798723 659352759 +1.63%
BenchmarkTemplate 112673009 112819078 +0.13%
Comparing tip (a27f34c771cb) against this CL on an Intel Xeon E5520:
BenchmarkBinaryTree17 5461110720 5393104469 -1.25%
BenchmarkFannkuch11 4314677151 4327177615 +0.29%
BenchmarkGobDecode 11065853 11235272 +1.53%
BenchmarkGobEncode 6500065 6959837 +7.07%
BenchmarkGzip 647478596 671769097 +3.75%
BenchmarkGunzip 139348579 141096376 +1.25%
BenchmarkHTTPClientServer 69376 73610 +6.10%
BenchmarkJSONEncode 30172320 31796106 +5.38%
BenchmarkJSONDecode 113704905 114239137 +0.47%
BenchmarkMandelbrot200 6032730 6003077 -0.49%
BenchmarkGoParse 6775251 6405995 -5.45%
BenchmarkRegexpMatchMedium_1K 111832 113895 +1.84%
BenchmarkRegexpMatchHard_1K 161112 168420 +4.54%
BenchmarkRevcomp 876363406 892319935 +1.82%
BenchmarkTemplate 146273096 148998339 +1.86%
Just to get a sense of where we are compared to the previous release,
here are the same benchmarks comparing Go 1.2 to this CL.
Comparing Go 1.2 against this CL on an Intel Core i5 MacBook Pro:
BenchmarkBinaryTree17 4370077662 3856337341 -11.76%
BenchmarkFannkuch11 3347052657 2991182127 -10.63%
BenchmarkGobDecode 8791384 8788340 -0.03%
BenchmarkGobEncode 4968759 5267394 +6.01%
BenchmarkGzip 437815669 434168065 -0.83%
BenchmarkGunzip 94604099 110563792 +16.87%
BenchmarkHTTPClientServer 87798 86131 -1.90%
BenchmarkJSONEncode 22818243 22501647 -1.39%
BenchmarkJSONDecode 97182444 85658808 -11.86%
BenchmarkMandelbrot200 4733516 4700108 -0.71%
BenchmarkGoParse 5054384 4712247 -6.77%
BenchmarkRegexpMatchMedium_1K 67612 73490 +8.69%
BenchmarkRegexpMatchHard_1K 107321 117495 +9.48%
BenchmarkRevcomp 733270055 659352759 -10.08%
BenchmarkTemplate 109304977 112819078 +3.21%
Comparing Go 1.2 against this CL on an Intel Xeon E5520:
BenchmarkBinaryTree17 5986953594 5393104469 -9.92%
BenchmarkFannkuch11 4861139174 4327177615 -10.98%
BenchmarkGobDecode 11830997 11235272 -5.04%
BenchmarkGobEncode 6608722 6959837 +5.31%
BenchmarkGzip 661875826 671769097 +1.49%
BenchmarkGunzip 138630019 141096376 +1.78%
BenchmarkHTTPClientServer 71534 73610 +2.90%
BenchmarkJSONEncode 30393609 31796106 +4.61%
BenchmarkJSONDecode 139645860 114239137 -18.19%
BenchmarkMandelbrot200 5988660 6003077 +0.24%
BenchmarkGoParse 6974092 6405995 -8.15%
BenchmarkRegexpMatchMedium_1K 111331 113895 +2.30%
BenchmarkRegexpMatchHard_1K 165961 168420 +1.48%
BenchmarkRevcomp 995049292 892319935 -10.32%
BenchmarkTemplate 145623363 148998339 +2.32%
Fixes#8036.
LGTM=khr
R=golang-codereviews, josharian, khr
CC=golang-codereviews, iant, r
https://golang.org/cl/99660044
[Same as CL 102820043 except applied changes to 6g/gsubr.c
also to 5g/gsubr.c and 8g/gsubr.c. The problem I had last night
trying to do that was that 8g's copy of nodarg has different
(but equivalent) control flow and I was pasting the new code
into the wrong place.]
Description from CL 102820043:
The 'nodarg' function is used to obtain a Node*
representing a function argument or result.
It returned a brand new Node*, but that violates
the guarantee in most places in the compiler that
two Node*s refer to the same variable if and only if
they are the same Node* pointer. Reestablish that
invariant by making nodarg return a preexisting
named variable if present.
Having fixed that, avoid any copy during x=x in
componentgen, because the VARDEF we emit
before the copy marks the lhs x as dead incorrectly.
The change in walk.c avoids modifying the result
of nodarg. This was the only place in the compiler
that did so.
Fixes#8097.
LGTM=khr
R=golang-codereviews, khr
CC=golang-codereviews, iant, khr, r
https://golang.org/cl/103750043
Breaks 386 and arm builds.
The obvious reason is that this CL only edited 6g/gsubr.c
and failed to edit 5g/gsubr.c and 8g/gsubr.c.
However, the obvious CL applying the same edit to those
files (CL 101900043) causes mysterious build failures
in various of the standard package tests, usually involving
reflect. Something deep and subtle is broken but only on
the 32-bit systems.
Undo this CL for now.
««« original CL description
cmd/gc: fix x=x crash
The 'nodarg' function is used to obtain a Node*
representing a function argument or result.
It returned a brand new Node*, but that violates
the guarantee in most places in the compiler that
two Node*s refer to the same variable if and only if
they are the same Node* pointer. Reestablish that
invariant by making nodarg return a preexisting
named variable if present.
Having fixed that, avoid any copy during x=x in
componentgen, because the VARDEF we emit
before the copy marks the lhs x as dead incorrectly.
The change in walk.c avoids modifying the result
of nodarg. This was the only place in the compiler
that did so.
Fixes#8097.
LGTM=r, khr
R=golang-codereviews, r, khr
CC=golang-codereviews, iant
https://golang.org/cl/102820043
»»»
TBR=r
CC=golang-codereviews, khr
https://golang.org/cl/95660043
The 'nodarg' function is used to obtain a Node*
representing a function argument or result.
It returned a brand new Node*, but that violates
the guarantee in most places in the compiler that
two Node*s refer to the same variable if and only if
they are the same Node* pointer. Reestablish that
invariant by making nodarg return a preexisting
named variable if present.
Having fixed that, avoid any copy during x=x in
componentgen, because the VARDEF we emit
before the copy marks the lhs x as dead incorrectly.
The change in walk.c avoids modifying the result
of nodarg. This was the only place in the compiler
that did so.
Fixes#8097.
LGTM=r, khr
R=golang-codereviews, r, khr
CC=golang-codereviews, iant
https://golang.org/cl/102820043
This matters for NaCl, which seems to swamp my 4-core MacBook Pro otherwise.
It's not a correctness problem, just a usability problem.
LGTM=bradfitz
R=bradfitz
CC=golang-codereviews
https://golang.org/cl/98600046
CL 51010045 fixed the first one of these:
cmd/gc: return canonical Node* from temp
For historical reasons, temp was returning a copy
of the created Node*, not the original Node*.
This meant that if analysis recorded information in the
returned node (for example, n->addrtaken = 1), the
analysis would not show up on the original Node*, the
one kept in fn->dcl and consulted during liveness
bitmap creation.
Correct this, and watch for it when setting addrtaken.
Fixes#7083.
R=khr, dave, minux.ma
CC=golang-codereviews
https://golang.org/cl/51010045
CL 53200043 fixed the second:
cmd/gc: fix race build
Missed this case in CL 51010045.
TBR=khr
CC=golang-codereviews
https://golang.org/cl/53200043
This CL fixes the third. There are only three nod(OXXX, ...)
calls in sinit.c, so maybe we're done. Embarassing that it
took three CLs to find all three.
Fixes#8028.
LGTM=khr
R=golang-codereviews, khr
CC=golang-codereviews, iant
https://golang.org/cl/100800046
In the first very rough draft of the reordering code
that was introduced in the Go 1.3 cycle, the pre-allocated
temporary for a ... argument was held in n->right.
It moved to n->alloc but the code avoiding n->right
was left behind in order.c. In copy(x, <-c), the receive
is in n->right and must be processed. Delete the special
case code, removing the bug.
Fixes#8039.
LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews
https://golang.org/cl/100820044
The code cannot have worked before, because it was
trying to use the old value in a range check for the new
type, which might have a different representation
(hence the 'internal compiler error').
Fixes#8073.
LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews
https://golang.org/cl/98630045
Add nacl.bash, the NaCl version of all.bash.
It's a separate script because it builds a variant of package syscall
with a large zip file embedded in it, containing all the input files
needed for tests.
Disable various tests new since the last round, mostly the ones using os/exec.
Fixes#7945.
LGTM=dave
R=golang-codereviews, remyoudompheng, dave, bradfitz
CC=golang-codereviews
https://golang.org/cl/100590044
I don't know when the bug was fixed, but empirically it was.
Make sure it stays fixed by adding a test.
Fixes#7884.
LGTM=adg
R=golang-codereviews, adg
CC=golang-codereviews
https://golang.org/cl/93500043
The float32 const conversion used to round to float64
and then use the hardware to round to float32.
Even though there was a range check before this
conversion, the double rounding introduced inaccuracy:
the round to float64 might round the value further away
from the float32 range, reaching a float64 value that
could not actually be rounded to float32. The hardware
appears to give us 0 in that case, but it is probably undefined.
Double rounding also meant that the wrong value might
be used for certain border cases.
Do the rounding the float32 ourselves, just as we already
did the rounding to float64. This makes the conversion
precise and also makes the conversion match the range check.
Finally, add some code to print very large (bigger than float64)
floating point constants in decimal floating point notation instead
of falling back to the precise but human-unreadable binary floating
point notation.
Fixes#8015.
LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews, r
https://golang.org/cl/100580044
The temporary-introducing pass was not recursing
into the argumnt of a receive operation.
Fixes#8011.
LGTM=r
R=golang-codereviews, r
CC=golang-codereviews, iant, khr
https://golang.org/cl/91540043
The introduction of temporaries in order.c was not
quite right for two corner cases:
1) The rewrite that pushed new variables on the lhs of
a receive into the body of the case was dropping the
declaration of the variables. If the variables escape,
the declaration is what allocates them.
Caught by escape analysis sanity check.
In fact the declarations should move into the body
always, so that we only allocate if the corresponding
case is selected. Do that. (This is an optimization that
was already present in Go 1.2. The new order code just
made it stop working.)
Fixes#7997.
2) The optimization to turn a single-recv select into
an ordinary receive assumed it could take the address
of the destination; not so if the destination is _.
Fixes#7998.
LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews
https://golang.org/cl/100480043
The GC program describing a data structure sometimes trusts the
pointer base type and other times does not (if not, the garbage collector
must fall back on per-allocation type information stored in the heap).
Make the scanning of a pointer in an interface do the same.
This fixes a crash in a particular use of reflect.SliceHeader.
Fixes#8004.
LGTM=khr
R=golang-codereviews, khr
CC=0xe2.0x9a.0x9b, golang-codereviews, iant, r
https://golang.org/cl/100470045
Globals, function arguments, and results are special cases in
registerization.
Globals must be flushed aggressively, because nearly any
operation can cause a panic, and the recovery code must see
the latest values. Globals also must be loaded aggressively,
because nearly any store through a pointer might be updating a
global: the compiler cannot see all the "address of"
operations on globals, especially exported globals. To
accomplish this, mark all globals as having their address
taken, which effectively disables registerization.
If a function contains a defer statement, the function results
must be flushed aggressively, because nearly any operation can
cause a panic, and the deferred code may call recover, causing
the original function to return the current values of its
function results. To accomplish this, mark all function
results as having their address taken if the function contains
any defer statements. This causes not just aggressive flushing
but also aggressive loading. The aggressive loading is
overkill but the best we can do in the current code.
Function arguments must be considered live at all safe points
in a function, because garbage collection always preserves
them: they must be up-to-date in order to be preserved
correctly. Accomplish this by marking them live at all call
sites. An earlier attempt at this marked function arguments as
having their address taken, which disabled registerization
completely, making programs slower. This CL's solution allows
registerization while preserving safety. The benchmark speedup
is caused by being able to registerize again (the earlier CL
lost the same amount).
benchmark old ns/op new ns/op delta
BenchmarkEqualPort32 61.4 56.0 -8.79%
benchmark old MB/s new MB/s speedup
BenchmarkEqualPort32 521.56 570.97 1.09x
Fixes#1304. (again)
Fixes#7944. (again)
Fixes#7984.
Fixes#7995.
LGTM=khr
R=golang-codereviews, khr
CC=golang-codereviews, iant, r
https://golang.org/cl/97500044
The inputs to a function are marked live at all times in the
liveness bitmaps, so that the garbage collector will not free
the things they point at and reuse the pointers, so that the
pointers shown in stack traces are guaranteed not to have
been recycled.
Unfortunately, no one told the register optimizer that the
inputs need to be preserved at all call sites. If a function
is done with a particular input value, the optimizer will stop
preserving it across calls. For single-word values this just
means that the value recorded might be stale. For multi-word
values like slices, the value recorded could be only partially stale:
it can happen that, say, the cap was updated but not the len,
or that the len was updated but not the base pointer.
Either of these possibilities (and others) would make the
garbage collector misinterpret memory, leading to memory
corruption.
This came up in a real program, in which the garbage collector's
'slice len ≤ slice cap' check caught the inconsistency.
Fixes#7944.
LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews, khr
https://golang.org/cl/100370045
This is joint work with Daniel Morsing.
In order for the register allocator to alias two variables, they must have the same width, stack offset, and etype. Code generation was altering a variable's etype in a few places. This prevented the variable from being moved to a register, which in turn prevented peephole optimization. This failure to alias was very common, with almost 23,000 instances just running make.bash.
This phenomenon was not visible in the register allocation debug output because the variables that failed to alias had the same name. The debugging-only change to bits.c fixes this by printing the variable number with its name.
This CL fixes the source of all etype mismatches for 6g, all but one case for 8g, and depressingly few cases for 5g. (I believe that extending CL 6819083 to 5g is a prerequisite.) Fixing the remaining cases in 8g and 5g is work for the future.
The etype mismatch fixes are:
* [gc] Slicing changed the type of the base pointer into a uintptr in order to perform arithmetic on it. Instead, support addition directly on pointers.
* [*g] OSPTR was giving type uintptr to slice base pointers; undo that. This arose, for example, while compiling copy(dst, src).
* [8g] 64 bit float conversion was assigning int64 type during codegen, overwriting the existing uint64 type.
Note that some etype mismatches are appropriate, such as a struct with a single field or an array with a single element.
With these fixes, the number of registerizations that occur while running make.bash for 6g increases ~10%. Hello world binary size shrinks ~1.5%. Running all benchmarks in the standard library show performance improvements ranging from nominal to substantive (>10%); a full comparison using 6g on my laptop is available at https://gist.github.com/josharian/8f9b5beb46667c272064. The microbenchmarks must be taken with a grain of salt; see issue 7920. The few benchmarks that show real regressions are likely due to issue 7920. I manually examined the generated code for the top few regressions and none had any assembly output changes. The few benchmarks that show extraordinary improvements are likely also due to issue 7920.
Performance results from 8g appear similar to 6g.
5g shows no performance improvements. This is not surprising, given the discussion above.
Update #7316
LGTM=rsc
R=rsc, daniel.morsing, bradfitz
CC=dave, golang-codereviews
https://golang.org/cl/91850043
Before we used line 1 of the first source file.
This should be clearer.
Fixes#4388.
LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews
https://golang.org/cl/92250044
If the ... element type contained no pointers,
then the escape analysis did not track the ... itself.
This manifested in an escaping ...byte being treated
as non-escaping.
Fixes#7934.
LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews
https://golang.org/cl/100310043
The register allocator decides which variables should be placed into registers by charging for each load/store and crediting for each use, and then selecting an allocation with minimal cost. NOPs will be eliminated, however, so using a variable in a NOP should not generate credit.
Issue 7867 arises from attempted registerization of multi-word variables because they are used in NOPs. By not crediting for that use, they will no longer be considered for registerization.
This fix could theoretically lead to better register allocation, but NOPs are rare relative to other instructions.
Fixes#7867.
LGTM=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/94810044
Variables declared with 'var' have no sym->def.
Fixes#7794.
LGTM=rsc
R=golang-codereviews, bradfitz, rsc
CC=golang-codereviews
https://golang.org/cl/88360043
The new code is adapted from the Go 1.2 nosplit code,
but it does not have the bug reported in issue 7623:
g% go run nosplit.go
g% go1.2 run nosplit.go
BUG
rejected incorrectly:
main 0 call f; f 120
linker output:
# _/tmp/go-test-nosplit021064539
main.main: nosplit stack overflow
120 guaranteed after split check in main.main
112 on entry to main.f
-8 after main.f uses 120
g%
Fixes#6931.
Fixes#7623.
LGTM=iant
R=golang-codereviews, iant, ality
CC=golang-codereviews, r
https://golang.org/cl/88190043
Trying to make GODEBUG=gcdead=1 work with liveness
and in particular ambiguously live variables.
1. In the liveness computation, mark all ambiguously live
variables as live for the entire function, except the entry.
They are zeroed directly after entry, and we need them not
to be poisoned thereafter.
2. In the liveness computation, compute liveness (and deadness)
for all parameters, not just pointer-containing parameters.
Otherwise gcdead poisons untracked scalar parameters and results.
3. Fix liveness debugging print for -live=2 to use correct bitmaps.
(Was not updated for compaction during compaction CL.)
4. Correct varkill during map literal initialization.
Was killing the map itself instead of the inserted value temp.
5. Disable aggressive varkill cleanup for call arguments if
the call appears in a defer or go statement.
6. In the garbage collector, avoid bug scanning empty
strings. An empty string is two zeros. The multiword
code only looked at the first zero and then interpreted
the next two bits in the bitmap as an ordinary word bitmap.
For a string the bits are 11 00, so if a live string was zero
length with a 0 base pointer, the poisoning code treated
the length as an ordinary word with code 00, meaning it
needed poisoning, turning the string into a poison-length
string with base pointer 0. By the same logic I believe that
a live nil slice (bits 11 01 00) will have its cap poisoned.
Always scan full multiword struct.
7. In the runtime, treat both poison words (PoisonGC and
PoisonStack) as invalid pointers that warrant crashes.
Manual testing as follows:
- Create a script called gcdead on your PATH containing:
#!/bin/bash
GODEBUG=gcdead=1 GOGC=10 GOTRACEBACK=2 exec "$@"
- Now you can build a test and then run 'gcdead ./foo.test'.
- More importantly, you can run 'go test -short -exec gcdead std'
to run all the tests.
Fixes#7676.
While here, enable the precise scanning of slices, since that was
disabled due to bugs like these. That now works, both with and
without gcdead.
Fixes#7549.
LGTM=khr
R=khr
CC=golang-codereviews
https://golang.org/cl/83410044
1. Use n->alloc, not n->left, to hold the allocated temp being
passed from orderstmt/orderexpr to walk.
2. Treat method values the same as closures.
3. Use killed temporary for composite literal passed to
non-escaping function argument.
4. Clean temporaries promptly in if and for statements.
5. Clean temporaries promptly in select statements.
As part of this, move all the temporary-generating logic
out of select.c into order.c, so that the temporaries can
be reclaimed.
With the new temporaries, can re-enable the 1-entry
select optimization. Fixes issue 7672.
While we're here, fix a 1-line bug in select processing
turned up by the new liveness test (but unrelated; select.c:72).
Fixes#7686.
6. Clean temporaries (but not particularly promptly) in switch
and range statements.
7. Clean temporary used during convT2E/convT2I.
8. Clean temporaries promptly during && and || expressions.
---
CL 81940043 reduced the number of ambiguously live temps
in the godoc binary from 860 to 711.
CL 83090046 reduced the number from 711 to 121.
This CL reduces the number from 121 to 23.
15 the 23 that remain are in fact ambiguously live.
The final 8 could be fixed but are not trivial and
not common enough to warrant work at this point
in the release cycle.
These numbers only count ambiguously live temps,
not ambiguously live user-declared variables.
There are 18 such variables in the godoc binary after this CL,
so a total of 41 ambiguously live temps or user-declared
variables.
The net effect is that zeroing anything on entry to a function
should now be a rare event, whereas earlier it was the
common case.
This is good enough for Go 1.3, and probably good
enough for future releases too.
Fixes#7345.
LGTM=khr
R=khr
CC=golang-codereviews
https://golang.org/cl/83000048
1. In functions with heap-allocated result variables or with
defer statements, the return sequence requires more than
just a single RET instruction. There is an optimization that
arranges for all returns to jump to a single copy of the return
epilogue in this case. Unfortunately, that optimization is
fundamentally incompatible with PC-based liveness information:
it takes PCs at many different points in the function and makes
them all land at one PC, making the combined liveness information
at that target PC a mess. Disable this optimization, so that each
return site gets its own copy of the 'call deferreturn' and the
copying of result variables back from the heap.
This removes quite a few spurious 'ambiguously live' variables.
2. Let orderexpr allocate temporaries that are passed by address
to a function call and then die on return, so that we can arrange
an appropriate VARKILL.
2a. Do this for ... slices.
2b. Do this for closure structs.
2c. Do this for runtime.concatstring, which is the implementation
of large string additions. Change representation of OADDSTR to
an explicit list in typecheck to avoid reconstructing list in both
walk and order.
3. Let orderexpr allocate the temporary variable copies used for
range loops, so that they can be killed when the loop is over.
Similarly, let it allocate the temporary holding the map iterator.
CL 81940043 reduced the number of ambiguously live temps
in the godoc binary from 860 to 711.
This CL reduces the number to 121. Still more to do, but another
good checkpoint.
Update #7345
LGTM=khr
R=khr
CC=golang-codereviews
https://golang.org/cl/83090046
The new channel and map runtime routines take pointers
to values, typically temporaries. Without help, the compiler
cannot tell when those temporaries stop being needed,
because it isn't sure what happened to the pointer.
Arrange to insert explicit VARKILL instructions for these
temporaries so that the liveness analysis can avoid seeing
them as "ambiguously live".
The change is made in order.c, which was already in charge of
introducing temporaries to preserve the order-of-evaluation
guarantees. Now its job has expanded to include introducing
temporaries as needed by runtime routines, and then also
inserting the VARKILL annotations for all these temporaries,
so that their lifetimes can be shortened.
In order to do its job for the map runtime routines, order.c arranges
that all map lookups or map assignments have the form:
x = m[k]
x, y = m[k]
m[k] = x
where x, y, and k are simple variables (often temporaries).
Likewise, receiving from a channel is now always:
x = <-c
In order to provide the map guarantee, order.c is responsible for
rewriting x op= y into x = x op y, so that m[k] += z becomes
t = m[k]
t2 = t + z
m[k] = t2
While here, fix a few bugs in order.c's traversal: it was failing to
walk into select and switch case bodies, so order of evaluation
guarantees were not preserved in those situations.
Added tests to test/reorder2.go.
Fixes#7671.
In gc/popt's temporary-merging optimization, allow merging
of temporaries with their address taken as long as the liveness
ranges do not intersect. (There is a good chance of that now
that we have VARKILL annotations to limit the liveness range.)
Explicitly killing temporaries cuts the number of ambiguously
live temporaries that must be zeroed in the godoc binary from
860 to 711, or -17%. There is more work to be done, but this
is a good checkpoint.
Update #7345
LGTM=khr
R=khr
CC=golang-codereviews
https://golang.org/cl/81940043
1. On entry to a function, only zero the ambiguously live stack variables.
Before, we were zeroing all stack variables containing pointers.
The zeroing is pretty inefficient right now (issue 7624), but there are also
too many stack variables detected as ambiguously live (issue 7345),
and that must be addressed before deciding how to improve the zeroing code.
(Changes in 5g/ggen.c, 6g/ggen.c, 8g/ggen.c, gc/pgen.c)
Fixes#7647.
2. Make the regopt word-based liveness analysis preserve the
whole-variable liveness property expected by the garbage collection
bitmap liveness analysis. That is, if the regopt liveness decides that
one word in a struct needs to be preserved, make sure it preserves
the entire struct. This is particularly important for multiword values
such as strings, slices, and interfaces, in which all the words need
to be present in order to understand the meaning.
(Changes in 5g/reg.c, 6g/reg.c, 8g/reg.c.)
Fixes#7591.
3. Make the regopt word-based liveness analysis treat a variable
as having its address taken - which makes it preserved across
all future calls - whenever n->addrtaken is set, for consistency
with the gc bitmap liveness analysis, even if there is no machine
instruction actually taking the address. In this case n->addrtaken
is incorrect (a nicer way to put it is overconservative), and ideally
there would be no such cases, but they can happen and the two
analyses need to agree.
(Changes in 5g/reg.c, 6g/reg.c, 8g/reg.c; test in bug484.go.)
Fixes crashes found by turning off "zero everything" in step 1.
4. Remove spurious VARDEF annotations. As the comment in
gc/pgen.c explains, the VARDEF must immediately precede
the initialization. It cannot be too early, and it cannot be too late.
In particular, if a function call sits between the VARDEF and the
actual machine instructions doing the initialization, the variable
will be treated as live during that function call even though it is
uninitialized, leading to problems.
(Changes in gc/gen.c; test in live.go.)
Fixes crashes found by turning off "zero everything" in step 1.
5. Do not treat loading the address of a wide value as a signal
that the value must be initialized. Instead depend on the existence
of a VARDEF or the first actual read/write of a word in the value.
If the load is in order to pass the address to a function that does
the actual initialization, treating the load as an implicit VARDEF
causes the same problems as described in step 4.
The alternative is to arrange to zero every such value before
passing it to the real initialization function, but this is a much
easier and more efficient change.
(Changes in gc/plive.c.)
Fixes crashes found by turning off "zero everything" in step 1.
6. Treat wide input parameters with their address taken as
initialized on entry to the function. Otherwise they look
"ambiguously live" and we will try to emit code to zero them.
(Changes in gc/plive.c.)
Fixes crashes found by turning off "zero everything" in step 1.
7. An array of length 0 has no pointers, even if the element type does.
Without this change, the zeroing code complains when asked to
clear a 0-length array.
(Changes in gc/reflect.c.)
LGTM=khr
R=khr
CC=golang-codereviews
https://golang.org/cl/80160044
Revision 3ae4607a43ff introduced CONVNOP layers
to fix type checking issues arising from comparisons.
The added complexity made 8g run out of registers
when compiling an equality function in go.net/ipv6.
A similar issue occurred in test/sizeof.go on
amd64p32 with 6g.
Fixes#7405.
LGTM=khr
R=rsc, dave, iant, khr
CC=golang-codereviews
https://golang.org/cl/78100044
A too large float constant is an error.
A too small float constant is rounded to zero.
Fixes#7419
Update #6902
LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews
https://golang.org/cl/76730046
The lowering to runtime calls introduces hidden pointers to the
arguments of select clauses. When implicit conversions were
involved it could end up with incompatible pointers. Since the
pointed-to types have the same representation, we can introduce a
forced conversion.
Fixes#6847.
LGTM=rsc
R=rsc, iant, khr
CC=golang-codereviews
https://golang.org/cl/72380043
The garbage collector uses type information to guide the
traversal of the heap. If it sees a field that should be a string,
it marks the object pointed at by the string data pointer as
visited but does not bother to look at the data, because
strings contain bytes, not pointers.
If you save s[len(s):] somewhere, though, the string data pointer
actually points just beyond the string data; if the string data
were exactly the size of an allocated block, the string data
pointer would actually point at the next block. It is incorrect
to mark that next block as visited and not bother to look at
the data, because the next block may be some other type
entirely.
The fix is to ignore strings with zero length during collection:
they are empty and can never become non-empty: the base
pointer will never be used again. The handling of slices already
does this (but using cap instead of len).
This was not a bug in Go 1.2, because until January all string
allocations included a trailing NUL byte not included in the
length, so s[len(s):] still pointed inside the string allocation
(at the NUL).
This bug was causing the crashes in test/run.go. Specifically,
the parsing of a regexp in package regexp/syntax allocated a
[]syntax.Inst with rounded size 1152 bytes. In fact it
allocated many such slices, because during the processing of
test/index2.go it creates thousands of regexps that are all
approximately the same complexity. That takes a long time, and
test/run works on other tests in other goroutines. One such
other test is chan/perm.go, which uses an 1152-byte source
file. test/run reads that file into a []byte and then calls
strings.Split(string(src), "\n"). The string(src) creates an
1152-byte string - and there's a very good chance of it
landing next to one of the many many regexp slices already
allocated - and then because the file ends in a \n,
strings.Split records the tail empty string as the final
element in the slice. A garbage collection happens at this
point, the collection finds that string before encountering
the []syntax.Inst data it now inadvertently points to, and the
[]syntax.Inst data is not scanned for the pointers that it
contains. Each syntax.Inst contains a []rune, those are
missed, and the backing rune arrays are freed for reuse. When
the regexp is later executed, the runes being searched for are
no longer runes at all, and there is no match, even on text
that should match.
On 64-bit machines the pointer in the []rune inside the
syntax.Inst is larger (along with a few other pointers),
pushing the []syntax.Inst backing array into a larger size
class, avoiding the collision with chan/perm.go's
inadvertently sized file.
I expect this was more prevalent on OS X than on Linux or
Windows because those managed to run faster or slower and
didn't overlap index2.go with chan/perm.go as often. On the
ARM systems, we only run one errorcheck test at a time, so
index2 and chan/perm would never overlap.
It is possible that this bug is the root cause of other crashes
as well. For now we only know it is the cause of the test/run crash.
Many thanks to Dmitriy for help debugging.
Fixes#7344.
Fixes#7455.
LGTM=r, dvyukov, dave, iant
R=golang-codereviews, dave, r, dvyukov, delpontej, iant
CC=golang-codereviews, khr
https://golang.org/cl/74250043
Some of the errorcheck tests have many many identical regexps.
Use a map to avoid storing the compiled form many many times
in memory. Change the filterRe to a simple string to avoid
the expense of those regexps as well.
Cuts the time for run.go on index2.go by almost 50x.
Noticed during debugging of issue 7344.
LGTM=bradfitz
R=bradfitz, josharian
CC=golang-codereviews
https://golang.org/cl/74380043
The byte that r is or'd into is already 0x7, so the failure to zero r only
impacts the generated machine code if the register is > 7.
Fixes#7044.
LGTM=dave, minux.ma, rsc
R=dave, minux.ma, bradfitz, rsc
CC=golang-codereviews
https://golang.org/cl/73730043
The cached computed interface tables are indexed by the interface
types, not by the unnamed underlying interfaces
To preserve the invariants expected by interface comparison, an
itab generated for an interface type must not be used for a value
of a different interface type even if the representation is identical.
Fixes#7207.
LGTM=rsc
R=rsc, iant, khr
CC=golang-codereviews
https://golang.org/cl/69210044
See golang.org/s/go13nacl for design overview.
This CL is the mostly mechanical changes from rsc's Go 1.2 based NaCl branch, specifically 39cb35750369 to 500771b477cf from https://code.google.com/r/rsc-go13nacl. This CL does not include working NaCl support, there are probably two or three more large merges to come.
CL 15750044 is not included as it involves more invasive changes to the linker which will need to be merged separately.
The exact change lists included are
15050047: syscall: support for Native Client
15360044: syscall: unzip implementation for Native Client
15370044: syscall: Native Client SRPC implementation
15400047: cmd/dist, cmd/go, go/build, test: support for Native Client
15410048: runtime: support for Native Client
15410049: syscall: file descriptor table for Native Client
15410050: syscall: in-memory file system for Native Client
15440048: all: update +build lines for Native Client port
15540045: cmd/6g, cmd/8g, cmd/gc: support for Native Client
15570045: os: support for Native Client
15680044: crypto/..., hash/crc32, reflect, sync/atomic: support for amd64p32
15690044: net: support for Native Client
15690048: runtime: support for fake time like on Go Playground
15690051: build: disable various tests on Native Client
LGTM=rsc
R=rsc
CC=golang-codereviews
https://golang.org/cl/68150047
Revision c0e0467635ec (cmd/gc: return canonical Node* from temp)
exposed original nodes of temporaries, allowing callers to mutate
their types.
In walkcompare a temporary could be typed as ideal because of
this. Additionnally, assignment of a comparison result to
a custom boolean type was broken.
Fixes#7366.
LGTM=rsc
R=rsc, iant, khr
CC=golang-codereviews
https://golang.org/cl/66930044
The error message was previously off by one in all cases.
Fixes#7150.
LGTM=r
R=golang-codereviews, r
CC=golang-codereviews
https://golang.org/cl/65850043
Update #6853
For an ephemeral binary - one created, run, and then deleted -
there is no need to write dwarf debug information, since the
binary will not be used with gdb. In this case, instruct the linker
not to spend time and disk space generating the debug information
by passing the -w flag to the linker.
Omitting dwarf information reduces the size of most binaries by 25%.
We may be more aggressive about this in the future.
LGTM=bradfitz, r
R=r, bradfitz
CC=golang-codereviews
https://golang.org/cl/65890043
Not recording the address being taken was causing
the liveness analysis not to preserve x in the absence
of direct references to x, which in turn was making the
net test fail with GOGC=0.
In addition to the test, this fixes a bug wherein
GOGC=0 go test -short net
crashed if liveness analysis was in use (like at tip, not like Go 1.2).
TBR=ken2
CC=golang-codereviews
https://golang.org/cl/64470043
The VARDEF placement must be before the initialization
but after any final use. If you have something like s = ... using s ...
the rhs must be evaluated, then the VARDEF, then the lhs
assigned.
There is a large comment in pgen.c on gvardef explaining
this in more detail.
This CL also includes Ian's suggestions from earlier CLs,
namely commenting the use of mode in link.h and fixing
the precedence of the ~r check in dcl.c.
This CL enables the check that if liveness analysis decides
a variable is live on entry to the function, that variable must
be a function parameter (not a result, and not a local variable).
If this check fails, it indicates a bug in the liveness analysis or
in the generated code being analyzed.
The race detector generates invalid code for append(x, y...).
The code declares a temporary t and then uses cap(t) before
initializing t. The new liveness check catches this bug and
stops the compiler from writing out the buggy code.
Consequently, this CL disables the race detector tests in
run.bash until the race detector bug can be fixed
(golang.org/issue/7334).
Except for the race detector bug, the liveness analysis check
does not detect any problems (this CL and the previous CLs
fixed all the detected problems).
The net test still fails with GOGC=0 but the rest of the tests
now pass or time out (because GOGC=0 is so slow).
TBR=iant
CC=golang-codereviews
https://golang.org/cl/64170043
The existing tests issue4463.go and issue4654.go had failures at
typechecking and did not test walking the AST.
Fixes#7272.
LGTM=khr
R=khr, rsc, iant
CC=golang-codereviews
https://golang.org/cl/60550044
When the liveness code doesn't know a function doesn't return
(but the generated code understands that), the liveness analysis
invents a control flow edge that is not really there, which can cause
variables to seem spuriously live. This is particularly bad when the
variables are uninitialized.
TBR=iant
CC=golang-codereviews
https://golang.org/cl/63720043
The registerization code needs the function to end in a RET,
even if that RET is actually unreachable.
The liveness code needs to avoid such unreachable RETs.
It had a special case for final RET after JMP, but no case
for final RET after UNDEF. Instead of expanding the special
cases, let fixjmp - which already knows what is and is not
reachable definitively - mark the unreachable RET so that
the liveness code can identify it.
TBR=iant
CC=golang-codereviews
https://golang.org/cl/63680043
A normal RET is treated as using the return values,
but a tail jump RET does not - it is jumping to the
function that is going to fill in the return values.
If a tail jump RET is recorded as using the return values,
since nothing initializes them they will be marked as
live on entry to the function, which is clearly wrong.
Found and tested by the new code in plive.c that looks
for variables that are incorrectly live on entry.
That code is disabled for now because there are other
cases remaining to be fixed. But once it is enabled,
test/live1.go becomes a real test of this CL.
TBR=iant
CC=golang-codereviews
https://golang.org/cl/63570045
Any initialization of a variable by a block copy or block zeroing
or by multiple assignments (componentwise copying or zeroing
of a multiword variable) needs to emit a VARDEF. These cases were not.
Fixes#7205.
TBR=iant
CC=golang-codereviews
https://golang.org/cl/63650044
Before, an unnamed return value turned into an ONAME node n with n->sym
named ~anon%d, and n->orig == n.
A blank-named return value turned into an ONAME node n with n->sym
named ~anon%d but n->orig == the original blank n. Code generation and
printing uses n->orig, so that this node formatted as _.
But some code does not use n->orig. In particular the liveness code does
not know about the n->orig convention and so mishandles blank identifiers.
It is possible to fix but seemed better to avoid the confusion entirely.
Now the first kind of node is named ~r%d and the second ~b%d; both have
n->orig == n, so that it doesn't matter whether code uses n or n->orig.
After this change the ->orig field is only used for other kinds of expressions,
not for ONAME nodes.
This requires distinguishing ~b from ~r names in a few places that care.
It fixes a liveness analysis bug without actually changing the liveness code.
TBR=ken2
CC=golang-codereviews
https://golang.org/cl/63630043
