This is an experiment in static analysis of Go programs
to understand which struct fields a program might use.
It is not part of the Go language specification, it must
be enabled explicitly when building the toolchain,
and it may be removed at any time.
After building the toolchain with GOEXPERIMENT=fieldtrack,
a specific field can be marked for tracking by including
`go:"track"` in the field tag:
package pkg
type T struct {
F int `go:"track"`
G int // untracked
}
To simplify usage, only named struct types can have
tracked fields, and only exported fields can be tracked.
The implementation works by making each function begin
with a sequence of no-op USEFIELD instructions declaring
which tracked fields are accessed by a specific function.
After the linker's dead code elimination removes unused
functions, the fields referred to by the remaining
USEFIELD instructions are the ones reported as used by
the binary.
The -k option to the linker specifies the fully qualified
symbol name (such as my/pkg.list) of a string variable that
should be initialized with the field tracking information
for the program. The field tracking string is a sequence
of lines, each terminated by a \n and describing a single
tracked field referred to by the program. Each line is made
up of one or more tab-separated fields. The first field is
the name of the tracked field, fully qualified, as in
"my/pkg.T.F". Subsequent fields give a shortest path of
reverse references from that field to a global variable or
function, corresponding to one way in which the program
might reach that field.
A common source of false positives in field tracking is
types with large method sets, because a reference to the
type descriptor carries with it references to all methods.
To address this problem, the CL also introduces a comment
annotation
//go:nointerface
that marks an upcoming method declaration as unavailable
for use in satisfying interfaces, both statically and
dynamically. Such a method is also invisible to package
reflect.
Again, all of this is disabled by default. It only turns on
if you have GOEXPERIMENT=fieldtrack set during make.bash.
R=iant, ken
CC=golang-dev
https://golang.org/cl/6749064
This patch is enough to fix compilation of
exp/types tests but only passes a stripped down
version of the appripriate torture test.
Update #4207.
R=dave, nigeltao, rsc, golang-dev
CC=golang-dev
https://golang.org/cl/6621061
In two cases, registers were allocated too early resulting
in exhausting of available registers when nesting these
operations.
The case of method calls was due to missing cases in igen,
which only makes calls but doesn't allocate a register for
the result.
The case of 8-bit multiplication was due to a wrong order
in register allocation when Ullman numbers were bigger on the
RHS.
Fixes#3907.
Fixes#4156.
R=rsc
CC=golang-dev, remy
https://golang.org/cl/6560054
This CL makes the compiler understand that the type of
the len or cap of a map, slice, or string is 'int', not 'int32'.
It does not change the meaning of int, but it should make
the eventual change of the meaning of int in 6g a bit smoother.
Update #2188.
R=ken, dave, remyoudompheng
CC=golang-dev
https://golang.org/cl/6542059
The width was not being set on the address, which meant
that the optimizer could not find variables that overlapped
with it and mark them as having had their address taken.
This let to the compiler believing variables had been set
but never used and then optimizing away the set.
Fixes#4129.
R=ken2
CC=golang-dev
https://golang.org/cl/6552059
It is enough to load directly the data word and the itab word
from memory, so we save a LEA instruction for each method call,
and allow elimination of some extra temporaries.
Update #1914.
R=daniel.morsing, rsc
CC=golang-dev, remy
https://golang.org/cl/6501110
Removes an extra LEAL/LEAQ instructions there and usually saves
a useless temporary in the idiom
if err := foo(); err != nil {...}
Generated code is also less involved:
MOVQ err+n(SP), AX
CMPQ AX, $0
(potentially CMPQ n(SP), $0) instead of
LEAQ err+n(SP), AX
CMPQ (AX), $0
Update #1914.
R=daniel.morsing, nigeltao, rsc
CC=golang-dev, remy
https://golang.org/cl/6493099
There may be further savings if convT2I can avoid the function call
if the cache is good and T is uintptr-shaped, a la convT2E, but that
will be a follow-up CL.
src/pkg/runtime:
benchmark old ns/op new ns/op delta
BenchmarkConvT2ISmall 43 15 -64.01%
BenchmarkConvT2IUintptr 45 14 -67.48%
BenchmarkConvT2ILarge 130 101 -22.31%
test/bench/go1:
benchmark old ns/op new ns/op delta
BenchmarkBinaryTree17 8588997000 8499058000 -1.05%
BenchmarkFannkuch11 5300392000 5358093000 +1.09%
BenchmarkGobDecode 30295580 31040190 +2.46%
BenchmarkGobEncode 18102070 17675650 -2.36%
BenchmarkGzip 774191400 771591400 -0.34%
BenchmarkGunzip 245915100 247464100 +0.63%
BenchmarkJSONEncode 123577000 121423050 -1.74%
BenchmarkJSONDecode 451969800 596256200 +31.92%
BenchmarkMandelbrot200 10060050 10072880 +0.13%
BenchmarkParse 10989840 11037710 +0.44%
BenchmarkRevcomp 1782666000 1716864000 -3.69%
BenchmarkTemplate 798286600 723234400 -9.40%
R=rsc, bradfitz, go.peter.90, daniel.morsing, dave, uriel
CC=golang-dev
https://golang.org/cl/6337058
Drop expecttaken function in favor of extra argument
to gbranch and bgen. Mark loop condition as likely to
be true, so that loops are generated inline.
The main benefit here is contiguous code when trying
to read the generated assembly. It has only minor effects
on the timing, and they mostly cancel the minor effects
that aligning function entry points had. One exception:
both changes made Fannkuch faster.
Compared to before CL 6244066 (before aligned functions)
benchmark old ns/op new ns/op delta
BenchmarkBinaryTree17 4222117400 4201958800 -0.48%
BenchmarkFannkuch11 3462631800 3215908600 -7.13%
BenchmarkGobDecode 20887622 20899164 +0.06%
BenchmarkGobEncode 9548772 9439083 -1.15%
BenchmarkGzip 151687 152060 +0.25%
BenchmarkGunzip 8742 8711 -0.35%
BenchmarkJSONEncode 62730560 62686700 -0.07%
BenchmarkJSONDecode 252569180 252368960 -0.08%
BenchmarkMandelbrot200 5267599 5252531 -0.29%
BenchmarkRevcomp25M 980813500 985248400 +0.45%
BenchmarkTemplate 361259100 357414680 -1.06%
Compared to tip (aligned functions):
benchmark old ns/op new ns/op delta
BenchmarkBinaryTree17 4140739800 4201958800 +1.48%
BenchmarkFannkuch11 3259914400 3215908600 -1.35%
BenchmarkGobDecode 20620222 20899164 +1.35%
BenchmarkGobEncode 9384886 9439083 +0.58%
BenchmarkGzip 150333 152060 +1.15%
BenchmarkGunzip 8741 8711 -0.34%
BenchmarkJSONEncode 65210990 62686700 -3.87%
BenchmarkJSONDecode 249394860 252368960 +1.19%
BenchmarkMandelbrot200 5273394 5252531 -0.40%
BenchmarkRevcomp25M 996013800 985248400 -1.08%
BenchmarkTemplate 360620840 357414680 -0.89%
R=ken2
CC=golang-dev
https://golang.org/cl/6245069
The old code generated for a bounds check was
CMP
JLT ok
CALL panicindex
ok:
...
The new code is (once the linker finishes with it):
CMP
JGE panic
...
panic:
CALL panicindex
which moves the calls out of line, putting more useful
code in each cache line. This matters especially in tight
loops, such as in Fannkuch. The benefit is more modest
elsewhere, but real.
From test/bench/go1, amd64:
benchmark old ns/op new ns/op delta
BenchmarkBinaryTree17 6096092000 6088808000 -0.12%
BenchmarkFannkuch11 6151404000 4020463000 -34.64%
BenchmarkGobDecode 28990050 28894630 -0.33%
BenchmarkGobEncode 12406310 12136730 -2.17%
BenchmarkGzip 179923 179903 -0.01%
BenchmarkGunzip 11219 11130 -0.79%
BenchmarkJSONEncode 86429350 86515900 +0.10%
BenchmarkJSONDecode 334593800 315728400 -5.64%
BenchmarkRevcomp25M 1219763000 1180767000 -3.20%
BenchmarkTemplate 492947600 483646800 -1.89%
And 386:
benchmark old ns/op new ns/op delta
BenchmarkBinaryTree17 6354902000 6243000000 -1.76%
BenchmarkFannkuch11 8043769000 7326965000 -8.91%
BenchmarkGobDecode 19010800 18941230 -0.37%
BenchmarkGobEncode 14077500 13792460 -2.02%
BenchmarkGzip 194087 193619 -0.24%
BenchmarkGunzip 12495 12457 -0.30%
BenchmarkJSONEncode 125636400 125451400 -0.15%
BenchmarkJSONDecode 696648600 685032800 -1.67%
BenchmarkRevcomp25M 2058088000 2052545000 -0.27%
BenchmarkTemplate 602140000 589876800 -2.04%
To implement this, two new instruction forms:
JLT target // same as always
JLT $0, target // branch expected not taken
JLT $1, target // branch expected taken
The linker could also emit the prediction prefixes, but it
does not: expected taken branches are reversed so that the
expected case is not taken (as in example above), and
the default expectaton for such a jump is not taken
already.
R=golang-dev, gri, r, dave
CC=golang-dev
https://golang.org/cl/6248049
* Eliminate bounds check on known small shifts.
* Rewrite x<<s | x>>(32-s) as a rotate (constant s).
* More aggressive (but still minimal) range analysis.
R=ken, dave, iant
CC=golang-dev
https://golang.org/cl/6209077
* Shift/rotate by constant doesn't have to stop subprop. (also in 8g)
* Remove redundant MOVLQZX instructions.
* An attempt at issuing loads early.
Good for 0.5% on a good day, might not be worth keeping.
Need to understand more about whether the x86
looks ahead to what loads might be coming up.
R=ken2, ken
CC=golang-dev
https://golang.org/cl/6203091
Such variables would be put at 0(SP), leading to serious
corruptions at zero initialization.
Fixes#3084.
R=golang-dev, r
CC=golang-dev, remy
https://golang.org/cl/5683052
The alternative is to record enough information that the
trap handler know which registers contain cached globals
and can flush the registers back to their original locations.
That's significantly more work.
This only affects globals that have been written to.
Code that reads from a global should continue to registerize
as well as before.
Fixes#1304.
R=ken2
CC=golang-dev
https://golang.org/cl/5687046
The garbage collector can avoid scanning this section, with
reduces collection time as well as the number of false positives.
Helps a little bit with issue 909, but certainly does not solve it.
R=ken2
CC=golang-dev
https://golang.org/cl/5671099
8g/cgen.c
print format type mismatch
8l/asm.c
resoff set and not used
gc/pgen.c
misleading comparison INT > 0x80000000
gc/reflect.c
dalgsym must be static to match forward declaration
gc/subr.c
assumed_equal set and not used
hashmem's second argument is not used
gc/walk.c
duplicated (unreachable) code
R=rsc
CC=golang-dev
https://golang.org/cl/5651079
If the values being compared have different concrete types,
then they're clearly unequal without needing to invoke the
actual interface compare routine. This speeds tests for
specific values, like if err == io.EOF, by about 3x.
benchmark old ns/op new ns/op delta
BenchmarkIfaceCmp100 843 287 -65.95%
BenchmarkIfaceCmpNil100 184 182 -1.09%
Fixes#2591.
R=ken2
CC=golang-dev
https://golang.org/cl/5651073
This changes makes constant propagation compare 'from' values using node
pointers rather than symbol names when checking to see whether a set
operation is redundant. When a function is inlined multiple times in a
calling function its arguments will share symbol names even though the values
are different. Prior to this fix the bug409 test would hit a case with 6g
where an LEAQ instruction was incorrectly eliminated from the second inlined
function call. 8g appears to have had the same bug, but the test did not fail
there.
R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/5646044
As a convenience to people working on the tools,
leave Makefiles that invoke the go dist tool appropriately.
They are not used during the build.
R=golang-dev, bradfitz, n13m3y3r, gustavo
CC=golang-dev
https://golang.org/cl/5636050
This can happen on Plan 9 if we we're building
with the 32-bit and 64-bit host compilers, one
after the other.
R=rsc
CC=golang-dev
https://golang.org/cl/5599053
Also delete gotest, since it's messy to fix and slated for deletion anyway.
A couple of things outside src can't be tested any more. "go test" will be
fixed and these tests will be re-enabled. They're noisy for now.
Fixes#284.
R=rsc
CC=golang-dev
https://golang.org/cl/5598049
This fixes issue 2444.
A big cleanup of all 31/32bit size boundaries i'll leave for another cl though. (see also issue 1700).
R=rsc
CC=golang-dev
https://golang.org/cl/5484058
To allow these types as map keys, we must fill in
equal and hash functions in their algorithm tables.
Structs or arrays that are "just memory", like [2]int,
can and do continue to use the AMEM algorithm.
Structs or arrays that contain special values like
strings or interface values use generated functions
for both equal and hash.
The runtime helper func runtime.equal(t, x, y) bool handles
the general equality case for x == y and calls out to
the equal implementation in the algorithm table.
For short values (<= 4 struct fields or array elements),
the sequence of elementwise comparisons is inlined
instead of calling runtime.equal.
R=ken, mpimenov
CC=golang-dev
https://golang.org/cl/5451105
The loop recognizer uses the standard dominance
frontiers but gets confused by dead code, which
has a (not explicitly set) rpo number of 0, meaning it
looks like the head of the function, so it dominates
everything. If the loop recognizer encounters dead
code while tracking backward through the graph
it fails to recognize where it started as a loop, and
then the optimizer does not registerize values loaded
inside that loop. Fix by checking rpo against rpo2r.
Separately, run a quick pass over the generated
code to squash JMPs to JMP instructions, which
are convenient to emit during code generation but
difficult to read when debugging the -S output.
A side effect of this pass is to eliminate dead code,
so the output files may be slightly smaller and the
optimizer may have less work to do.
There is no semantic effect, because the linkers
flatten JMP chains and delete dead instructions
when laying out the final code. Doing it here too
just makes the -S output easier to read and more
like what the final binary will contain.
The "dead code breaks loop finding" bug is thus
fixed twice over. It seemed prudent to fix loopit
separately just in case dead code ever sneaks back
in for one reason or another.
R=ken2
CC=golang-dev
https://golang.org/cl/5190043
My previous CL:
changeset: 9645:ce2e5f44b310
user: Russ Cox <rsc@golang.org>
date: Tue Sep 06 10:24:21 2011 -0400
summary: gc: unify stack frame layout
introduced a bug wherein no variables were
being registerized, making Go programs 2-3x
slower than they had been before.
This CL fixes that bug (along with some others
it was hiding) and adds a test that optimization
makes at least one test case faster.
R=ken2
CC=golang-dev
https://golang.org/cl/5174045
allocparams + tempname + compactframe
all knew about how to place stack variables.
Now only compactframe, renamed to allocauto,
does the work. Until the last minute, each PAUTO
variable is in its own space and has xoffset == 0.
This might break 5g. I get failures in concurrent
code running under qemu and I can't tell whether
it's 5g's fault or qemu's. We'll see what the real
ARM builders say.
R=ken2
CC=golang-dev
https://golang.org/cl/4973057
Does as much as possible in data layout instead
of during the init function.
Handles var x = y; var y = z as a special case too,
because it is so prevalent in package unicode
(var Greek = _Greek; var _Greek = []...).
Introduces InitPlan description of initialized data
so that it can be traversed multiple times (for example,
in the copy handler).
Cuts package unicode's init function size by 8x.
All that remains there is map initialization, which
is on the chopping block too.
Fixes sinit.go test case.
Aggregate DATA instructions at end of object file.
Checkpoint. More to come.
R=ken2
CC=golang-dev
https://golang.org/cl/4969051
8g/cgen.c:
8g/gobj.c
. dropped unnecessary assignments;
8g/gg.h
. added varargckk pragmas;
8g/ggen.c
. dropped duplicate assignment;
8g/gsubr.c
. adjusted format in print statement;
. dropped unnecessary assignment;
. replaced GCC's _builtin_return_address(0) with Plan 9's
getcallerpc(&n) which is defined as a macro in <u.h>;
8g/list.c
. adjusted format in snprint statement;
8g/opt.h
. added varargck pragma (Adr*) that is specific for the invoking
modules;
8g/peep.c
. dropped unnecessary incrementation;
R=rsc
CC=golang-dev
https://golang.org/cl/4974044
#include "go.h" (or "gg.h")
becomes
#include <u.h>
#include <libc.h>
#include "go.h"
so that go.y can #include <stdio.h>
after <u.h> but before "go.h".
This is necessary on Plan 9.
R=ken2
CC=golang-dev
https://golang.org/cl/4971041
Required moving some parts of gc/pgen.c to ?g/ggen.c
on linux tests pass for all 3 architectures, and
frames are actually compacted (diagnostic code for
that has been removed from the CL).
R=rsc
CC=golang-dev
https://golang.org/cl/4571071
After allocparams and walk, remove unused auto variables
and re-layout the remaining in reverse alignment order.
R=rsc
CC=golang-dev
https://golang.org/cl/4568068
Input code like
0000 (x.go:2) TEXT main+0(SB),$36-0
0001 (x.go:3) MOVL $5,i+-8(SP)
0002 (x.go:3) MOVL $0,i+-4(SP)
0003 (x.go:4) MOVL $1,BX
0004 (x.go:4) MOVL i+-8(SP),AX
0005 (x.go:4) MOVL i+-4(SP),DX
0006 (x.go:4) MOVL AX,autotmp_0000+-20(SP)
0007 (x.go:4) MOVL DX,autotmp_0000+-16(SP)
0008 (x.go:4) MOVL autotmp_0000+-20(SP),CX
0009 (x.go:4) CMPL autotmp_0000+-16(SP),$0
0010 (x.go:4) JNE ,13
0011 (x.go:4) CMPL CX,$32
0012 (x.go:4) JCS ,14
0013 (x.go:4) MOVL $0,BX
0014 (x.go:4) SHLL CX,BX
0015 (x.go:4) MOVL BX,x+-12(SP)
0016 (x.go:5) MOVL x+-12(SP),AX
0017 (x.go:5) CDQ ,
0018 (x.go:5) MOVL AX,autotmp_0001+-28(SP)
0019 (x.go:5) MOVL DX,autotmp_0001+-24(SP)
0020 (x.go:5) MOVL autotmp_0001+-28(SP),AX
0021 (x.go:5) MOVL autotmp_0001+-24(SP),DX
0022 (x.go:5) MOVL AX,(SP)
0023 (x.go:5) MOVL DX,4(SP)
0024 (x.go:5) CALL ,runtime.printint+0(SB)
0025 (x.go:5) CALL ,runtime.printnl+0(SB)
0026 (x.go:6) RET ,
is problematic because the liveness range for
autotmp_0000 (0006-0009) is nested completely
inside a span where BX holds a live value (0003-0015).
Because the register allocator only looks at 0006-0009
to see which registers are used, it misses the fact that
BX is unavailable and uses it anyway.
The n->pun = anyregalloc() check in tempname is
a workaround for this bug, but I hit it again because
I did the tempname call before allocating BX, even
though I then used the temporary after storing in BX.
This should fix the real bug, and then we can remove
the workaround in tempname.
The code creates pseudo-variables for each register
and includes that information in the liveness propagation.
Then the regu fields can be populated using that more
complete information. With that approach, BX is marked
as in use on every line in the whole span 0003-0015,
so that the decision about autotmp_0000
(using only 0006-0009) still has all the information
it needs.
This is not specific to the 386, but it only happens in
generated code of the form
load R1
...
load var into R2
...
store R2 back into var
...
use R1
and for the most part the other compilers generate
the loads for a given compiled line before any of
the stores. Even so, this may not be the case everywhere,
so the change is worth making in all three.
R=ken2, ken, ken
CC=golang-dev
https://golang.org/cl/4529106
The code for converting negative floats was
incorrectly loading an FP control word from
the stack without ever having stored it there.
Thanks to Lars Pensjö for reporting this bug.
R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/4515091
Also, 6g was passing uninitialized
Node &n2 to regalloc, causing non-deterministic
register collisions (but only when both left and
right hand side of comparison had function calls).
Fixes#1728.
R=ken2
CC=golang-dev
https://golang.org/cl/4425070
The ld time was dominated by symbol table processing, so
* increase hash table size
* emit fewer symbols in gc (just 1 per string, 1 per type)
* add read-only lookup to avoid creating spurious symbols
* add linked list to speed whole-table traversals
Breaks dwarf generator (no idea why), so disable dwarf.
Reduces time for 6l to link godoc by 25%.
R=ken2
CC=golang-dev
https://golang.org/cl/4383047
The recent linker changes broke NaCl support
a month ago, and there are no known users of it.
The NaCl code can always be recovered from the
repository history.
R=adg, r
CC=golang-dev
https://golang.org/cl/3671042
No semantic changes here, but working
toward being able to align structs based
on the maximum alignment of the fields
inside instead of having a fixed alignment
for all structs (issue 482).
R=ken2
CC=golang-dev
https://golang.org/cl/3617041
If an %lld argument can be 32 or 64 bits wide, cast to vlong.
If always 32 bits, drop the ll.
Fixes#1336.
R=brainman, rsc
CC=golang-dev
https://golang.org/cl/3580041
Just enough to make mov instructions work,
which in turn is enough to make strconv work
when it avoids any floating point calculations.
That makes a bunch of other packages pass
their tests.
Should suffice until hardware floating point
is available.
Enable package tests that now pass
(some due to earlier fixes).
Looks like there is a new integer math bug
exposed in the fmt and json tests.
R=ken2
CC=golang-dev
https://golang.org/cl/2638041
The Plan 9 tools assume that long is 32 bits.
We converted all instances of long to int32 when
importing the code but missed the print formats.
Because int32 is always int on the compilers we use,
it is never correct to use %lux, %ld, etc. Convert to %ux, %d, etc.
(It matters because on 64-bit gcc, long is 64 bits,
so we were printing 32-bit quantities with 64-bit formats.)
R=ken2
CC=golang-dev
https://golang.org/cl/2491041
x.go:13: cannot use t (type T) as type Reader in assignment:
T does not implement Reader (Read method requires pointer receiver)
x.go:19: cannot use q (type Q) as type Reader in assignment:
Q does not implement Reader (missing Read method)
have read()
want Read()
x.go:22: cannot use z (type int) as type Reader in assignment:
int does not implement Reader (missing Read method)
x.go:24: too many arguments to conversion to complex: complex(1, 3)
R=ken2
CC=golang-dev
https://golang.org/cl/1736041
cannot allocate an audomatic temp
while real registers are allocated.
there is a chance that the automatic
will be allocated to one of the
allocated registers. the fix is to
not registerize such variables.
R=rsc
CC=golang-dev
https://golang.org/cl/1202042
5g/6g/8g: add import statements to export metadata, mapping package path to package name.
recognize "" as the path of the package in export metadata.
use "" as the path of the package in object symbol names.
5c/6c/8c, 5a/6a/8a: rewrite leading . to "". so that ·Sin means Sin in this package.
5l/6l/8l: rewrite "" in symbol names as object files are read.
gotest: handle new symbol names.
gopack: handle new import lines in export metadata.
Collectively, these changes eliminate the assumption of a global
name space in the object file formats. Higher level pieces such as
reflect and the computation of type hashes still depend on the
assumption; we're not done yet.
R=ken2, r, ken3
CC=golang-dev
https://golang.org/cl/186263
* switch to real dot (.) instead of center dot (·) everywhere in object files.
before it was half and half depending on where in the name it appeared.
* in 6c/6a/etc identifiers, · can still be used but turns into . immediately.
* in export metadata, replace package identifiers with quoted strings
(still package names, not paths).
R=ken2, r
CC=golang-dev
https://golang.org/cl/190076
Using FUCOMIP instead of the FUCOMP-FSTSW-SAHF sequence gives better performance and saves code space.
R=rsc
CC=golang-dev
https://golang.org/cl/183139
UTF-8 string, Yconv() converts it into an octal sequence. If the
string converted to more than 30 bytes, the str buffer would
overflow. For example, 4 Greek runes became 32 bytes, 3 Hiragana
runes became 36 bytes, and 2 Gothic runes became 32 bytes. In
8l, 6l and 5l the function is Sconv(). For some reason, only 5l uses
the constant STRINGSZ (defined as 200) for the buffer size.
R=rsc
https://golang.org/cl/168045
the bash scripts and makefiles for building go didn't take into account
the fact $GOROOT / $GOBIN could both be directories containing whitespaces,
and was not possible to build it in such a situation.
this commit adjusts the various makefiles/scripts to make it aware of that
possibility, and now it builds successfully when using a path with whitespaces
as well.
Fixes#115.
R=rsc, dsymonds1
https://golang.org/cl/157067
* add runtime sliceslice1 for x[lo:]
* remove runtime arraytoslice, rewriting &arr into arr[0:len(arr)].
* port cgen_inline into 8g, 5g.
* use native memmove in maps
R=ken2
https://golang.org/cl/157106
