Merge dev.ssa branch back into master.

Change-Id: Ie6fac3f8d355ab164f934415fe4fc7fcb8c3db16

Static branch predictions (which guide block ordering) are
adjusted based on:

loop/not-loop     (favor looping)
abnormal-exit/not (avoid panic)
call/not-call     (avoid call)
ret/default       (treat returns as rare)

This appears to make no difference in performance of real
code, meaning the compiler itself.  The earlier version of
this has been stripped down to help make the cost of this
only-aesthetic-on-Intel phase be as cheap as possible (we
probably want information about inner loops for improving
register allocation, but because register allocation follows
close behind this pass, conceivably the information could be
reused -- so we might do this anyway just to normalize
output).

For a ./make.bash that takes 200 user seconds, about .75
second is reported in likelyadjust (summing nanoseconds
reported with -d=ssa/likelyadjust/time ).

Upstream predictions are respected.
Includes test, limited to build on amd64 only.
Did several iterations on the debugging output to allow
some rough checks on behavior.
Debug=1 logging notes agree/disagree with earlier passes,
allowing analysis like the following:

Run on make.bash:
GO_GCFLAGS=-d=ssa/likelyadjust/debug \
   ./make.bash >& lkly5.log

grep 'ranch prediction' lkly5.log | wc -l
   78242 // 78k predictions

grep 'ranch predi' lkly5.log | egrep -v 'agrees with' | wc -l
   29633 // 29k NEW predictions

grep 'disagrees' lkly5.log | wc -l
     444 // contradicted 444 times

grep '< exit' lkly5.log | wc -l
   10212 // 10k exit predictions

grep '< exit' lkly5.log | egrep 'disagrees' | wc -l
       5 // 5 contradicted by previous prediction

grep '< exit' lkly5.log | egrep -v 'agrees' | wc -l
     702 // 702-5 redundant with previous prediction

grep '< call' lkly5.log | egrep -v 'agrees' | wc -l
   16699 // 16k new call predictions

grep 'stay in loop' lkly5.log | egrep -v 'agrees' | wc -l
    3951 // 4k new "remain in loop" predictions

Fixes #11451.

Change-Id: Iafb0504f7030d304ef4b6dc1aba9a5789151a593
Reviewed-on: https://go-review.googlesource.com/19995
Run-TryBot: David Chase <drchase@google.com>
Reviewed-by: Keith Randall <khr@golang.org>

Add a blank line before the "package ssa" lines so the "autogenerated
don't edit" comments don't end up in godoc output.

Change-Id: I82bf90d52d426ce1a8e21483fc8f47b3689259c7
Reviewed-on: https://go-review.googlesource.com/20086Reviewed-by: Keith Randall <khr@golang.org>

Change-Id: I1ece7463d35efba0e8d2b1e61727dd25283ff720
Reviewed-on: https://go-review.googlesource.com/20059Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: David Crawshaw <crawshaw@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

* Decreases the generated code slightly.
* Similar to phiopt pass from gcc, except it only handles
booleans. Handling Eq/Neq had no impact on the generated code.

name       old time/op     new time/op     delta
Template       453ms ± 4%      451ms ± 4%    ~           (p=0.468 n=24+24)
GoTypes        1.55s ± 1%      1.55s ± 2%    ~           (p=0.287 n=24+25)
Compiler       6.53s ± 2%      6.56s ± 1%  +0.46%        (p=0.050 n=23+23)
MakeBash       45.8s ± 2%      45.7s ± 2%    ~           (p=0.866 n=24+25)

name       old text-bytes  new text-bytes  delta
HelloSize       676k ± 0%       676k ± 0%    ~     (all samples are equal)
CmdGoSize      8.07M ± 0%      8.07M ± 0%  -0.03%        (p=0.000 n=25+25)

Change-Id: Ia62477b7554127958a14cb27f85849b095d63663
Reviewed-on: https://go-review.googlesource.com/20090Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Alexandru Moșoi <alexandru@mosoi.ro>
TryBot-Result: Gobot Gobot <gobot@golang.org>

* This is a very basic form of straight line strength reduction.
* Removes one multiplication from a[b].c++; a[b+1].c++
* It increases pressure on the register allocator because
CSE creates more copies of the multiplication sizeof(a[0])*b.

Change-Id: I686a18e9c24cc6f8bdfa925713afed034f7d36d0
Reviewed-on: https://go-review.googlesource.com/20091
Run-TryBot: Alexandru Moșoi <alexandru@mosoi.ro>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

Writing to low 8/16 bits of register creates false dependency
Generate 32-bit operations when possible.

Change-Id: I8eb6c1c43a66424eec6baa91a660bceb6b80d1d3
Reviewed-on: https://go-review.googlesource.com/19506Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Ilya Tocar <ilya.tocar@intel.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Change-Id: I5546c4e8092ef61648cdae9c04288bb7d6f32476
Reviewed-on: https://go-review.googlesource.com/20084
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Dave Cheney <dave@cheney.net>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Use only reflect.TypeOf to detect if argument is a string.

The wasString return is only needed in doPrint with the 'v' verb.
This type of string detection is handled correctly by reflect.TypeOf
which is used already in doPrint for identifying a string argument.

Remove now obsolete wasString computations and return values.

Change-Id: Iea2de7ac0f5c536a53eec63f7e679d628f5af8dc
Reviewed-on: https://go-review.googlesource.com/19976
Run-TryBot: Rob Pike <r@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>

Updates #13940.

Change-Id: I41974c292dd981d82ac03b9b8b406713445362c3
Reviewed-on: https://go-review.googlesource.com/20081
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Change-Id: I99c737415a082df883a9c12cdb43bdd5a1b9a8ad
Reviewed-on: https://go-review.googlesource.com/20082Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Also, relocate related const and type definitions from go.go.

Change-Id: Ieb9b672da8dd510ca67022b4f7ae49a778a56579
Reviewed-on: https://go-review.googlesource.com/20080
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Dave Cheney <dave@cheney.net>
Reviewed-by: Keith Randall <khr@golang.org>

Change-Id: I2d8efef333f2441da6742e125e23ff57c9853ebd
Reviewed-on: https://go-review.googlesource.com/20078
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Dave Cheney <dave@cheney.net>

Change-Id: I42f370b987fcc85201f7aaa055b9e58ee9b9a99e
Reviewed-on: https://go-review.googlesource.com/20079
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Dave Cheney <dave@cheney.net>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Fixes #14371

Change-Id: I8e9e4b2b89083f5a947e791c011912fdf365a11e
Reviewed-on: https://go-review.googlesource.com/19996Reviewed-by: Andrew Gerrand <adg@golang.org>

Add writeback code to each return location which copies
the final result back to the correct stack location.

Cgo plays tricky games by taking the address of a
in f(a int) (b int) and then using that address to
modify b.  So for cgo-generated Go code, disable the
SSAing of output args.

Update #14511

Change-Id: I95cba727d53699d31124eef41db0e03935862be9
Reviewed-on: https://go-review.googlesource.com/19988Reviewed-by: Todd Neal <todd@tneal.org>
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

Fixes #14570.

Change-Id: Ief84a14585bfc209e38cdf15702c2f54ba759714
Reviewed-on: https://go-review.googlesource.com/20057
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Hudson-Doyle <michael.hudson@canonical.com>

In best of 10, linking cmd/go shows a ~10% improvement.

tip:              real  0m1.152s user  0m1.005s
this:             real  0m1.065s user  0m0.924s

Change-Id: I303a20b94332feaedc1033c453247a0e4c05c843
Reviewed-on: https://go-review.googlesource.com/19978Reviewed-by: David Crawshaw <crawshaw@golang.org>

The cache gets a 62% hit rate while compiling
the standard library.


name      old time/op    new time/op    delta
Template     449ms ± 2%     443ms ± 4%  -1.40%  (p=0.006 n=23+25)
GoTypes      1.54s ± 1%     1.50s ± 2%  -2.53%  (p=0.000 n=22+22)
Compiler     5.51s ± 1%     5.39s ± 1%  -2.29%  (p=0.000 n=23+25)

name      old alloc/op   new alloc/op   delta
Template    90.4MB ± 0%    90.0MB ± 0%  -0.45%  (p=0.000 n=25+25)
GoTypes      334MB ± 0%     331MB ± 0%  -1.05%  (p=0.000 n=25+25)
Compiler    1.12GB ± 0%    1.10GB ± 0%  -1.57%  (p=0.000 n=25+24)

name      old allocs/op  new allocs/op  delta
Template      681k ± 0%      682k ± 0%  +0.26%  (p=0.000 n=25+25)
GoTypes      2.23M ± 0%     2.23M ± 0%  +0.05%  (p=0.000 n=23+24)
Compiler     6.46M ± 0%     6.46M ± 0%  +0.02%  (p=0.000 n=24+25)


Change-Id: I2629c291892827493d7b55ec4d83f6973a2ab133
Reviewed-on: https://go-review.googlesource.com/20026Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Alexandru Moșoi <alexandru@mosoi.ro>
TryBot-Result: Gobot Gobot <gobot@golang.org>

(Last?) Semi-regular merge from tip to dev.ssa.

Conflicts:
	src/cmd/compile/internal/gc/closure.go
	src/cmd/compile/internal/gc/gsubr.go
	src/cmd/compile/internal/gc/lex.go
	src/cmd/compile/internal/gc/pgen.go
	src/cmd/compile/internal/gc/syntax.go
	src/cmd/compile/internal/gc/walk.go
	src/cmd/internal/obj/pass.go

Change-Id: Ib5ea8bf74d420f4902a9c6208761be9f22371ae7

It gets rewritten to an xor by the linker also.

Change-Id: Iae35130325d41bd1a09b7e971190cae6f4e17fac
Reviewed-on: https://go-review.googlesource.com/20058Reviewed-by: David Chase <drchase@google.com>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

The object file reader in cmd/link reads the symbol name into a scratch
[]byte, converts it to a string, and then does a substring replacement.
Instead, this CL does the replacement on the []byte into the scratch
space and then creates the final string.

Linking godoc without DWARF, best of ten, shows a ~10% improvement.

tip:           real 0m1.099s user 0m1.541s
this:          real 0m0.990s user 0m1.280s

This is part of an attempt to make suffixarray string deduping
come out as a wash, but it's not there yet:

cl/19987:      real 0m1.335s user 0m1.794s
cl/19987+this: real 0m1.225s user 0m1.540s

Change-Id: Idf061fdfbd7f08aa3a1f5933d3f111fdd1659210
Reviewed-on: https://go-review.googlesource.com/20025Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: David Crawshaw <crawshaw@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

The Cpos function is used frequently (at least once per symbol) and
it is implemented with the seek syscall. Instead, track current
output offset and use it.

Building the godoc binary with DWARF, best of ten:

tip:  real 0m1.287s user 0m1.573s
this: real 0m1.208s user 0m1.555s

Change-Id: I068148695cd6b4d32cd145db25e59e6f6bae6945
Reviewed-on: https://go-review.googlesource.com/20055
Run-TryBot: David Crawshaw <crawshaw@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Change-Id: Ib0dd458d4ab1c58a2baf36491e288ac32e2ff99e
Reviewed-on: https://go-review.googlesource.com/19962Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Reduces number of memory allocations by 12%:

Before: 1816664
After:  1581591

Small speed improvement.

Change-Id: I61281fb852e8e31851a350e3ae756676705024a4
Reviewed-on: https://go-review.googlesource.com/20027Reviewed-by: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Update #14559.

Change-Id: I92603602e5d0a5fcae43f3084f234ff606447190
Reviewed-on: https://go-review.googlesource.com/20056
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Reduces best of 10 linking of cmd/go by ~5%

Change-Id: If673b877ee12595dae517d7eb48430451e5cadba
Reviewed-on: https://go-review.googlesource.com/20060Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: David Crawshaw <crawshaw@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Preallocate ~2MB for Lsym map (size calculation from http://play.golang.org/p/9L7F5naXRr).
Reduces best of 10 link time of cmd/go by ~4%.
On cmd/go max resident size unaffected, on println hello world max resident size grows by 4mb from 18mb->22mb. Performance improves in both cases.

tip:  real  0m1.283s user  0m1.502s sys 0m0.144s
this: real  0m1.341s user  0m1.598s sys 0m0.136s

Change-Id: I4a95e45fe552f1f64f53e868421b9f45a34f8b96
Reviewed-on: https://go-review.googlesource.com/19979
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Crawshaw <crawshaw@golang.org>

In golang.org/cl/14449 the `getdents' system call got changed to use
_SYS_getdents as a layer of indirection instead of SYS_GETDENTS64 for
compatibility with mips64, but this broke mksyscall.pl, which then
died with with:
  syscall_linux.go:840: malformed //sys declaration

Change-Id: Icb61965d8730f6e81f9fb0fa28c7bab635470f09
Reviewed-on: https://go-review.googlesource.com/20051Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Update #14559.

Change-Id: I8894f8e16902685f55a21d902199fbe0905f0558
Reviewed-on: https://go-review.googlesource.com/20050
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>

This is a AMD64 version of CL19743.
Saves additional 1574 bytes in go binary.
This also speeds up bzip2 by 1-4%

Change-Id: I031ba423663c4e83fdefe44e5296f24143e303da
Reviewed-on: https://go-review.googlesource.com/19939
Run-TryBot: Ilya Tocar <ilya.tocar@intel.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

Movups is 1 byte smaller than movapd that we currently use.

Change-Id: I22f771f066529352722a28543535ec43497cb9c5
Reviewed-on: https://go-review.googlesource.com/19938Reviewed-by: David Chase <drchase@google.com>

Named returned values should only be used on public funcs and methods
when it contributes to the documentation.

Named return values should not be used if they're only saving the
programmer a few lines of code inside the body of the function,
especially if that means there's stutter in the documentation or it
was only there so the programmer could use a naked return
statement. (Naked returns should not be used except in very small
functions)

This change is a manual audit & cleanup of public func signatures.

Signatures were not changed if:

* the func was private (wouldn't be in public godoc)
* the documentation referenced it
* the named return value was an interesting name. (i.e. it wasn't
  simply stutter, repeating the name of the type)

There should be no changes in behavior. (At least: none intended)

Change-Id: I3472ef49619678fe786e5e0994bdf2d9de76d109
Reviewed-on: https://go-review.googlesource.com/20024
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Andrew Gerrand <adg@golang.org>

Fixes #14557.

Change-Id: I9610b79aafe9c15f9c998739b586fd0b41b90d70
Reviewed-on: https://go-review.googlesource.com/20031Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Mostly renaming variables for clarity.

Passes toolstash -cmp.

Change-Id: I9867137c34c14985cbbbdb2d34fbbe4cc65cb6fb
Reviewed-on: https://go-review.googlesource.com/20023Reviewed-by: Ian Lance Taylor <iant@golang.org>

Passes toolstash -cmp.

Casual timings show about a 3% improvement in compile times.

Update #14473.

Change-Id: I584add2e8f1a52486ba418b25ba6122b7347b643
Reviewed-on: https://go-review.googlesource.com/19989Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Do not replace the sign in front of a number with a space if both
f.space and f.plus are both specified for number formatting.
This was already the case for integers but not for floats
and complex numbers.

Updates: #14543.

Change-Id: I07ddeb505003db84a8a7d2c743dc19fc427a00bd
Reviewed-on: https://go-review.googlesource.com/19974
Run-TryBot: Rob Pike <r@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>

Besides being more efficient in a large build, this avoids a possible
race when creating the input file.

Change-Id: Ifc2cb055925a76be9c90eac56d84ebd9e14f2bbc
Reviewed-on: https://go-review.googlesource.com/19392Reviewed-by: Michael Hudson-Doyle <michael.hudson@canonical.com>

Avoid targeting a partial register with load;
ensure source of load (writebarrier) is aligned.

Better yet would be "CMPB $1,writebarrier" but that requires
wrestling with flagalloc (mem operand complicates moving
instruction around).

Didn't see a change in time for
   benchcmd -n 10 Build go build net/http

Verified that we clean the code up properly:
   0x20a8 <main.main+104>:	mov    0xc30a2(%rip),%eax
                            # 0xc5150 <runtime.writeBarrier>
   0x20ae <main.main+110>:	test   %al,%al

Change-Id: Id5fb8c260eaec27bd727cb0ae1476c60343b0986
Reviewed-on: https://go-review.googlesource.com/19998Reviewed-by: Keith Randall <khr@golang.org>