There is a special case for slicing s[i:j] when the resulting
slice has zero capacity, to prevent pointing to the next object
in memory.

Change this special case code from:
  rptr := rcap == 0 ? ptr : ptr+i*elemsize
to
  rptr := ptr + (rcap == 0 ? 0 : i) * elemsize

This change leads to slightly smaller generated code, replacing
a load with a register zero.

old:
	0x002e 00046 (slice.go:8)	CMPQ	BX, $0
	0x0032 00050 (slice.go:8)	JEQ	$0, 78
	0x0034 00052 (slice.go:8)	MOVQ	"".a+8(FP), BP
	0x0039 00057 (slice.go:8)	LEAQ	(BP)(CX*8), AX
	0x003e 00062 ... rest of function ...

	0x004e 00078 (slice.go:7)	MOVQ	"".a+8(FP), AX
	0x0053 00083 (slice.go:8)	JMP	62

new:
	0x002e 00046 (slice.go:8)	CMPQ	BX, $0
	0x0032 00050 (slice.go:8)	JEQ	$0, 78
	0x0034 00052 (slice.go:8)	MOVQ	"".a+8(FP), BP
	0x0039 00057 (slice.go:8)	LEAQ	(BP)(CX*8), AX
	0x003e 00062 ... rest of function...

	0x004e 00078 (slice.go:8)	MOVQ	$0, CX
	0x0050 00080 (slice.go:8)	JMP	52

Change-Id: I2a396616b0d7b090c226a47c92a7ba14b128401f
Reviewed-on: https://go-review.googlesource.com/20994Reviewed-by: David Chase <drchase@google.com>

Fixes #14901

Change-Id: Ia32e09767374a341c9a36c5d977d47d7d1a82315
Reviewed-on: https://go-review.googlesource.com/20967Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: David Crawshaw <crawshaw@golang.org>

Should let the s390x builder progress a little further.

Change-Id: I5eab5f384b0b039f8e246ba69ecfb24de08625d2
Reviewed-on: https://go-review.googlesource.com/20965Reviewed-by: Minux Ma <minux@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Allow names to be used for subexpressions of match rules.
For example:

(OpA x:(OpB y)) -> ..use x here to refer to the OpB value..

This gets rid of the .Args[0].Args[0]... way of naming we
used to use.

While we're here, give all subexpression matches names instead
of recomputing them with .Args[i] sequences each time they
are referenced.  Makes the generated rule code a bit smaller.

Change-Id: Ie42139f6f208933b75bd2ae8bd34e95419bc0e4e
Reviewed-on: https://go-review.googlesource.com/20997
Run-TryBot: Todd Neal <todd@tneal.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Todd Neal <todd@tneal.org>

Don't write back parts of a slicing operation if they
are unchanged from the source of the slice.  For example:

x.s = x.s[0:5]         // don't write back pointer or cap
x.s = x.s[:5]          // don't write back pointer or cap
x.s = x.s[:5:7]        // don't write back pointer

There is more to be done here, for example:

x.s = x.s[:len(x.s):7] // don't write back ptr or len

This CL can't handle that one yet.

Fixes #14855

Change-Id: Id1e1a4fa7f3076dc1a76924a7f1cd791b81909bb
Reviewed-on: https://go-review.googlesource.com/20954Reviewed-by: Austin Clements <austin@google.com>
Run-TryBot: Keith Randall <khr@golang.org>

For the following example, but there are a few more in the stdlib:
func histogram(b []byte, h *[256]int32) {
        for _, t := range b {
                h[t]++
        }
}

Change-Id: I56615f341ae52e02ef34025588dc6d1c52122295
Reviewed-on: https://go-review.googlesource.com/20924Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Alexandru Moșoi <alexandru@mosoi.ro>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Allow inlining of functions with switch statements as long as they don't
contain a break or type switch.

Fixes #13071

Change-Id: I057be351ea4584def1a744ee87eafa5df47a7f6d
Reviewed-on: https://go-review.googlesource.com/20824Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Converting a big.Float value x to a float32/64 value did not correctly
round x up to the smallest denormal float32/64 if x was smaller than the
smallest denormal float32/64, but larger than 0.5 of a smallest denormal
float32/64.

Handle this case explicitly and simplify some code in the turn.

For #14651.

Change-Id: I025e24bf8f0e671581a7de0abf7c1cd7e6403a6c
Reviewed-on: https://go-review.googlesource.com/20816
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Alan Donovan <adonovan@google.com>

The inserted early bound checks cause the slice
to expand beyond the original length of the slice.

Change-Id: Ib38891605f4a9a12d3b9e2071a5f77640b083d2d
Reviewed-on: https://go-review.googlesource.com/20981Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Minux Ma <minux@golang.org>

MOVSB is quite a bit faster for unaligned moves.
Possibly we should use MOVSB all of the time, but Intel folks
say it might be a bit faster to use MOVSQ on some processors
(but not any I have access to at the moment).

benchmark                              old ns/op     new ns/op     delta
BenchmarkMemmove4096-8                 93.9          93.2          -0.75%
BenchmarkMemmoveUnalignedDst4096-8     256           151           -41.02%
BenchmarkMemmoveUnalignedSrc4096-8     175           90.5          -48.29%

Fixes #14630

Change-Id: I568e6d6590eb3615e6a699fb474020596be665ff
Reviewed-on: https://go-review.googlesource.com/20293Reviewed-by: Ian Lance Taylor <iant@golang.org>

Passes toolstash -cmp.

Change-Id: I8725dee490778be9c1fd31990a6b27df9713c3c9
Reviewed-on: https://go-review.googlesource.com/20957Reviewed-by: Ian Lance Taylor <iant@golang.org>

Left over from CL 20931.

Change-Id: I3b8dd9ef748bcbf70b5118da28135aaa1e5ba3a8
Reviewed-on: https://go-review.googlesource.com/20955
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Minux Ma <minux@golang.org>

Constant comparisons against 0 are reasonably common.
Special-case and avoid allocating a new zero value each time.

Change-Id: I6c526c8ab30ef7f0fef59110133c764b7b90ba05
Reviewed-on: https://go-review.googlesource.com/20956Reviewed-by: Alan Donovan <adonovan@google.com>

Also give them more idiomatic Go names. Adding godocs is outside the
scope of this CL. (Besides, the method names almost all directly
parallel an underlying math/big.Int or math/big.Float method.)

CL prepared mechanically with sed (for rewriting mpint.go/mpfloat.go)
and gofmt (for rewriting call sites).

Passes toolstash -cmp.

Change-Id: Id76f4aee476ba740f48db33162463e7978c2083d
Reviewed-on: https://go-review.googlesource.com/20909
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

Fixed bug that slipped probably slipped in after rebasing and
explain why it failed on nacl/netbsd/plan9, which set default
maxparallelism to 1.

Change-Id: I4d59682fb2843d138b320334189f53fcdda5b2f6
Reviewed-on: https://go-review.googlesource.com/20980
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

Fixes #14890.

Change-Id: Ie790276b0e2ef94c92db3a777042d750269f876a
Reviewed-on: https://go-review.googlesource.com/20953Reviewed-by: Alan Donovan <adonovan@google.com>

The Linux ABI takes arguments in a different order on s390x.

Change-Id: Ic9cfcc22a5ea3d8ef77d4dd0b915fc266ff3e5f7
Reviewed-on: https://go-review.googlesource.com/20960Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>

Minimum architecture of z196 required so that GCC can assemble
gcc_s390x.S in runtime/cgo.

Change-Id: I603ed2edd39f826fb8193740ece5bd11d18c3dc5
Reviewed-on: https://go-review.googlesource.com/20876Reviewed-by: Ian Lance Taylor <iant@golang.org>

Updates #10848

Change-Id: I8353100ed01cb0e8fc19225157f5709bae388612
Reviewed-on: https://go-review.googlesource.com/20975Reviewed-by: Rob Pike <r@golang.org>

Fixes this test on s390x.

Change-Id: Ie5b70e8191169867765ec9248d827ca12c6405f4
Reviewed-on: https://go-review.googlesource.com/20964Reviewed-by: Minux Ma <minux@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Change-Id: I928532b406a3457d2c5f75f4de7d46a3f795192e
Reviewed-on: https://go-review.googlesource.com/20939Reviewed-by: Minux Ma <minux@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>

It was just a funny way of saying len(Ctxt.Allsym) by now.

Change-Id: Iff75e73c9f7ec4ba26cfef479bbd05d7dcd172f5
Reviewed-on: https://go-review.googlesource.com/20973
Run-TryBot: Michael Hudson-Doyle <michael.hudson@canonical.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Nothing cares about it.

I did this after looking at the memprof output, but it helps performance a bit:

name       old s/op    new s/op    delta
LinkCmdGo   0.44 ± 3%   0.43 ± 3%  -2.20%   (p=0.000 n=94+90)
LinkJuju    3.98 ± 5%   3.94 ± 5%  -1.19%  (p=0.000 n=100+91)

As well as MaxRSS (i.e. what /usr/bin/time -f '%M' prints):

name       old MaxRSS  new MaxRSS  delta
LinkCmdGo   130k ± 0%   120k ± 3%  -7.79%   (p=0.000 n=79+90)
LinkJuju    862k ± 6%   827k ± 8%  -4.01%  (p=0.000 n=100+99)

Change-Id: I6306b7b3369576a688659e2ecdb0815b4152ae96
Reviewed-on: https://go-review.googlesource.com/20972
Run-TryBot: Michael Hudson-Doyle <michael.hudson@canonical.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Change-Id: I0ea74dc1b11fad8ded9e649a3c1e4213ea6639b8
Reviewed-on: https://go-review.googlesource.com/20974
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Change-Id: Iedd01ef3a9d2831cb55c53b7a1984e7e932f4249
Reviewed-on: https://go-review.googlesource.com/20932Reviewed-by: Ian Lance Taylor <iant@golang.org>

Introduce garbage-free LookupN to replace most users of Lookupf.

Also, remove the string interning from LookupBytes which was hurting
more than helping.

name       old alloc/op    new alloc/op    delta
Template      63.0MB ± 0%     62.7MB ± 0%  -0.48%         (p=0.000 n=10+9)
Unicode       43.0MB ± 0%     43.0MB ± 0%  -0.17%         (p=0.000 n=10+7)
GoTypes        219MB ± 0%      218MB ± 0%  -0.14%        (p=0.000 n=10+10)
Compiler       992MB ± 0%      991MB ± 0%  -0.12%        (p=0.000 n=10+10)

name       old allocs/op   new allocs/op   delta
Template        683k ± 0%       681k ± 0%  -0.38%         (p=0.000 n=10+8)
Unicode         541k ± 0%       541k ± 0%  -0.11%        (p=0.000 n=10+10)
GoTypes        2.09M ± 0%      2.08M ± 0%  -0.40%        (p=0.000 n=10+10)
Compiler       9.28M ± 0%      9.24M ± 0%  -0.36%        (p=0.000 n=10+10)

Size of $GOROOT/pkg/darwin_amd64 drops from 40124 KB to 40100 KB too,
removing the zero padding as suggested by josharian.

Updates #6853

Change-Id: I3c557266e9325fe29c459cef8e5b8954913e7abb
Reviewed-on: https://go-review.googlesource.com/20931Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Allows the compiler to recognise s390x specific files and s390x
build tags.

Change-Id: I7c62ab7361cf708181b1d9cfbe9b1fcb01be31e0
Reviewed-on: https://go-review.googlesource.com/20872Reviewed-by: Minux Ma <minux@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

This deletes unused code and helpers from tests.

Change-Id: Ie31d46115f558ceb8da6efbf90c3c204e03b0d7e
Reviewed-on: https://go-review.googlesource.com/20927Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

An instruction consisting of all 0s causes an illegal instruction
signal on s390x. Since 0s are the default in this test this CL just
makes it explicit.

Change-Id: Id6e060eed1a588f4b10a4e4861709fcd19b434ac
Reviewed-on: https://go-review.googlesource.com/20962Reviewed-by: Minux Ma <minux@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Change-Id: I39aa6569c9a6f327f7aaa01f8b4ace814fd5b766
Reviewed-on: https://go-review.googlesource.com/20943Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Debugasm can never be set in cmd/link, so delete it and the code it enables.

Change-Id: If828db0b09f1a9e512dc660ac2750657a769094c
Reviewed-on: https://go-review.googlesource.com/20971
Run-TryBot: Michael Hudson-Doyle <michael.hudson@canonical.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

This expression in readsym:

    dup != nil && len(dup.P) > 0 && strings.HasPrefix(s.Name, "gclocals·")

can never be true: if dup != nil, then s.Name is ".dup" (and this is not new:
the same broken logic is present in 1.4, at least). Delete the whole block.

Change-Id: I33b14d9a82b292116d6fd79d22b38e3842501317
Reviewed-on: https://go-review.googlesource.com/20970
Run-TryBot: Michael Hudson-Doyle <michael.hudson@canonical.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

The obj.Nocache helper was only used by the arm back end, move it there.

Change-Id: I5c9faf995499991ead1f3d8c8ffc3b6af7346876
Reviewed-on: https://go-review.googlesource.com/20868Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Add a special helper for its one external use.

This is in preparation for an upcoming CL.

Passes toolstash -cmp / buildall.

Change-Id: I9d3463792afe220cc4bc89269bdecf0279abd281
Reviewed-on: https://go-review.googlesource.com/20933
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

This CL addresses a long standing CL by rsc by pushing the use of
Link.Windows down to its two users.

Link.Window was always initalised with the value of runtime.GOOS so
this does not affect cross compilation.

Change-Id: Ibbae068f8b5aad06336909691f094384caf12352
Reviewed-on: https://go-review.googlesource.com/20869
Run-TryBot: Dave Cheney <dave@cheney.net>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

'b' is a standard verb for floating point values. The runes like '+'
and '#' are called "flags" by package fmt's documentation. The flag
'-' controls left/right justification, not anything related to signs.

Change-Id: Ia9cf81b002df373f274ce635fe09b5bd0066aa1c
Reviewed-on: https://go-review.googlesource.com/20930Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Another object file change, gives a reasonable improvement:

name       old s/op   new s/op   delta
LinkCmdGo  0.46 ± 3%  0.44 ± 9%  -3.34%  (p=0.000 n=98+82)
LinkJuju   4.09 ± 4%  3.92 ± 5%  -4.30%  (p=0.000 n=98+99)

I guess the data section could be mmap-ed instead of read, I haven't tried
that.

Change-Id: I959eee470a05526ab1579e3f5d3ede41c16c954f
Reviewed-on: https://go-review.googlesource.com/20928
Run-TryBot: Michael Hudson-Doyle <michael.hudson@canonical.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Crawshaw <crawshaw@golang.org>

In tests TransportPersistConnLeak and TransportPersistConnLeakShortBody,
there's a fixed wait time (100ms and 400ms respectively) to allow
goroutines to exit after CloseIdleConnections is called. This
is sometimes too short on a slow host running many simultaneous
tests.

This CL replaces the fixed sleep in each test with a sequence of
shorter sleeps, testing the number of remaining goroutines until
it reaches the threshold or an overall time limit of 500ms expires.
This prevents some failures in the plan9_arm builder, while reducing
the test time on faster machines.

Fixes #14887

Change-Id: Ia5c871062df139e2667cdfb2ce8283e135435318
Reviewed-on: https://go-review.googlesource.com/20922
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Fixes #14849

Change-Id: I86e2dc27ca73bb6b24261a68cbf0094a63167414
Reviewed-on: https://go-review.googlesource.com/20833Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Alexandru Moșoi <alexandru@mosoi.ro>
TryBot-Result: Gobot Gobot <gobot@golang.org>

For a long time varexpr has handled ODOT incorrectly: it has always
returned false.  Before https://golang.org/cl/20890 this has been
because an ODOT had a Right field with an ONAME with no Class, for which
varexpr returns false.  CL 20890 preserved the behavior of varexpr for
ODOT, so that the change would pass toolstash -cmp.

This CL fixes varexpr so that ODOT can return true in some cases.  This
breaks toolstash -cmp.  While the changed compiler allocates temporary
variables in a different order, I have not been able to find any
examples where the generated code is different, other than using
different stack offsets and, in some cases, registers.  It seems that
other parts of the compiler will force the ODOT into a temporary anyhow.

Still, this change is clearly correct, and is a minor compiler cleanup.

Change-Id: I71506877aa3c13966bb03c281aa16271ee7fe80a
Reviewed-on: https://go-review.googlesource.com/20907
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: David Crawshaw <crawshaw@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>