The current phiopt pass just transforms the following code
  x := false
  if b { x = true}
into
  x = b

But we find code in runtime.atoi like this:
  neg := false
  if s[0] == '-' {
    neg = true
    s = s[1:]
  }

The current phiopt pass does not covert it into code like:
  neg := s[0] == '-'
  if neg { s = s[1:] }

Therefore, this patch strengthens the phiopt pass so that the
boolean Phi value "neg" can be replaced with a copy of control
value "s[0] == '-'", thereby using "cmp+cset" instead of a branch.

But in some cases even replacing the boolean Phis cannot eliminate
this branch. In the following case, this patch replaces "d" with a
copy of "a<0", but the regalloc pass will insert the "Load {c}"
value into an empty block to split the live ranges, which causes
the branch to not be eliminated.

For example:
  func test(a, b, c int) (bool, int) {
    d := false
    if (a<0) {
      if (b<0) {
        c = c+1
      }
      d = true
    }
    return d, c
  }

The optimized assembly code:
  MOVD "".a(FP), R0
  TBZ $63, R0, 48
  MOVD "".c+16(FP), R1
  ADD $1, R1, R2
  MOVD "".b+8(FP), R3
  CMP ZR, R3
  CSEL LT, R2, R1, R1
  CMP ZR, R0
  CSET LT, R0
  MOVB R0, "".~r3+24(FP)
  MOVD R1, "".~r4+32(FP)
  RET (R30)
  MOVD "".c+16(FP), R1
  JMP 28

The benchmark:

name          old time/op            new time/op            delta
pkg:cmd/compile/internal/ssa goos:linux goarch:arm64
PhioptPass  117783.250000ns +- 1%  117219.111111ns +- 1%   ~  (p=0.074  n=8+9)

Statistical data from compilecmp tool:

compilecmp local/master -> HEAD
local/master (a826f7dc45): debug/dwarf: support DW_FORM_rnglistx aka formRnglistx
HEAD (e57e003c10): cmd/compile/internal/ssa: strengthen phiopt pass

benchstat -geomean  /tmp/2516644532 /tmp/1075915815
completed 50 of 50, estimated time remaining 0s (ETA 7:10PM)
name                      old time/op       new time/op       delta
Template                        554ms _ 3%        553ms _ 3%    ~     (p=0.986 n=49+48)
Unicode                         252ms _ 4%        249ms _ 4%  -1.33%  (p=0.002 n=47+49)
GoTypes                         3.16s _ 3%        3.18s _ 3%  +0.77%  (p=0.022 n=44+48)
Compiler                        257ms _ 4%        258ms _ 4%    ~     (p=0.121 n=50+49)
SSA                             24.2s _ 4%        24.2s _ 5%    ~     (p=0.694 n=49+50)
Flate                           338ms _ 4%        338ms _ 4%    ~     (p=0.592 n=43+46)
GoParser                        506ms _ 3%        507ms _ 3%    ~     (p=0.942 n=49+50)
Reflect                         1.37s _ 4%        1.37s _ 5%    ~     (p=0.408 n=50+50)
Tar                             486ms _ 3%        487ms _ 4%    ~     (p=0.911 n=47+50)
XML                             619ms _ 2%        619ms _ 3%    ~     (p=0.368 n=46+48)
LinkCompiler                    1.29s _31%        1.32s _23%    ~     (p=0.306 n=49+44)
ExternalLinkCompiler            3.39s _10%        3.36s _ 6%    ~     (p=0.311 n=48+46)
LinkWithoutDebugCompiler        846ms _37%        793ms _24%  -6.29%  (p=0.040 n=50+49)
[Geo mean]                      974ms             971ms       -0.36%

name                      old user-time/op  new user-time/op  delta
Template                        910ms _12%        893ms _13%    ~     (p=0.098 n=49+49)
Unicode                         495ms _28%        492ms _18%    ~     (p=0.562 n=50+46)
GoTypes                         4.42s _15%        4.39s _13%    ~     (p=0.684 n=49+50)
Compiler                        419ms _22%        422ms _16%    ~     (p=0.579 n=48+50)
SSA                             36.5s _ 7%        36.6s _ 8%    ~     (p=0.465 n=50+47)
Flate                           521ms _21%        523ms _16%    ~     (p=0.889 n=50+47)
GoParser                        810ms _12%        792ms _15%    ~     (p=0.149 n=50+50)
Reflect                         1.98s _13%        2.02s _13%    ~     (p=0.144 n=47+50)
Tar                             826ms _15%        806ms _19%    ~     (p=0.115 n=49+49)
XML                             988ms _14%       1003ms _14%    ~     (p=0.179 n=50+50)
LinkCompiler                    1.79s _ 8%        1.84s _11%  +2.81%  (p=0.001 n=49+49)
ExternalLinkCompiler            3.69s _ 4%        3.71s _ 3%    ~     (p=0.261 n=50+50)
LinkWithoutDebugCompiler        838ms _10%        827ms _11%    ~     (p=0.323 n=50+48)
[Geo mean]                      1.44s             1.44s       -0.05%

name                      old alloc/op      new alloc/op      delta
Template                       39.0MB _ 1%       39.0MB _ 1%    ~     (p=0.445 n=50+49)
Unicode                        28.5MB _ 0%       28.5MB _ 0%    ~     (p=0.460 n=50+50)
GoTypes                         169MB _ 1%        169MB _ 1%    ~     (p=0.092 n=48+50)
Compiler                       23.4MB _ 1%       23.4MB _ 1%  -0.19%  (p=0.032 n=50+49)
SSA                            1.54GB _ 0%       1.55GB _ 1%  +0.14%  (p=0.001 n=50+50)
Flate                          23.8MB _ 1%       23.8MB _ 2%    ~     (p=0.702 n=49+49)
GoParser                       35.4MB _ 1%       35.4MB _ 1%    ~     (p=0.786 n=50+50)
Reflect                        85.3MB _ 1%       85.3MB _ 1%    ~     (p=0.298 n=50+50)
Tar                            34.6MB _ 2%       34.6MB _ 2%    ~     (p=0.683 n=50+50)
XML                            44.5MB _ 3%       44.0MB _ 2%  -1.05%  (p=0.000 n=50+46)
LinkCompiler                    136MB _ 0%        136MB _ 0%  +0.01%  (p=0.005 n=50+50)
ExternalLinkCompiler            128MB _ 0%        128MB _ 0%    ~     (p=0.179 n=50+50)
LinkWithoutDebugCompiler       84.3MB _ 0%       84.3MB _ 0%  +0.01%  (p=0.006 n=50+50)
[Geo mean]                     70.7MB            70.6MB       -0.07%

name                      old allocs/op     new allocs/op     delta
Template                         410k _ 0%         410k _ 0%    ~     (p=0.606 n=48+49)
Unicode                          310k _ 0%         310k _ 0%    ~     (p=0.674 n=50+50)
GoTypes                         1.81M _ 0%        1.81M _ 0%    ~     (p=0.674 n=50+50)
Compiler                         202k _ 0%         202k _ 0%  +0.02%  (p=0.046 n=50+50)
SSA                             16.3M _ 0%        16.3M _ 0%  +0.10%  (p=0.000 n=50+50)
Flate                            244k _ 0%         244k _ 0%    ~     (p=0.834 n=49+50)
GoParser                         380k _ 0%         380k _ 0%    ~     (p=0.410 n=50+50)
Reflect                         1.08M _ 0%        1.08M _ 0%    ~     (p=0.782 n=48+50)
Tar                              368k _ 0%         368k _ 0%    ~     (p=0.585 n=50+49)
XML                              453k _ 0%         453k _ 0%  -0.01%  (p=0.025 n=49+49)
LinkCompiler                     713k _ 0%         713k _ 0%  +0.01%  (p=0.044 n=50+50)
ExternalLinkCompiler             794k _ 0%         794k _ 0%  +0.01%  (p=0.000 n=50+49)
LinkWithoutDebugCompiler         251k _ 0%         251k _ 0%    ~     (p=0.092 n=47+50)
[Geo mean]                       615k              615k       +0.01%

name                      old maxRSS/op     new maxRSS/op     delta
Template                        37.0M _ 4%        37.2M _ 3%    ~     (p=0.062 n=48+48)
Unicode                         36.9M _ 5%        37.3M _ 4%  +1.10%  (p=0.021 n=50+47)
GoTypes                         94.3M _ 3%        94.9M _ 4%  +0.69%  (p=0.022 n=45+46)
Compiler                        33.4M _ 3%        33.4M _ 5%    ~     (p=0.964 n=49+50)
SSA                              741M _ 3%         738M _ 3%    ~     (p=0.164 n=50+50)
Flate                           28.5M _ 6%        28.8M _ 4%  +1.07%  (p=0.009 n=50+49)
GoParser                        35.0M _ 3%        35.3M _ 4%  +0.83%  (p=0.010 n=50+48)
Reflect                         57.2M _ 6%        57.1M _ 4%    ~     (p=0.815 n=50+49)
Tar                             34.9M _ 3%        35.0M _ 3%    ~     (p=0.134 n=49+48)
XML                             39.5M _ 5%        40.0M _ 3%  +1.35%  (p=0.001 n=50+48)
LinkCompiler                     220M _ 2%         220M _ 2%    ~     (p=0.547 n=49+48)
ExternalLinkCompiler             235M _ 2%         236M _ 2%    ~     (p=0.538 n=47+44)
LinkWithoutDebugCompiler         179M _ 1%         179M _ 1%    ~     (p=0.775 n=50+50)
[Geo mean]                      74.9M             75.2M       +0.43%

name                      old text-bytes    new text-bytes    delta
HelloSize                       784kB _ 0%        784kB _ 0%  +0.01%  (p=0.000 n=50+50)

name                      old data-bytes    new data-bytes    delta
HelloSize                      13.1kB _ 0%       13.1kB _ 0%    ~     (all equal)

name                      old bss-bytes     new bss-bytes     delta
HelloSize                       206kB _ 0%        206kB _ 0%    ~     (all equal)

name                      old exe-bytes     new exe-bytes     delta
HelloSize                      1.28MB _ 0%       1.28MB _ 0%  +0.00%  (p=0.000 n=50+50)

file      before    after     _       %
addr2line 4006300   4004484   -1816   -0.045%
api       5029956   5029324   -632    -0.013%
asm       4936311   4939423   +3112   +0.063%
buildid   2595059   2595291   +232    +0.009%
cgo       4401029   4397333   -3696   -0.084%
compile   22246677  22246863  +186    +0.001%
cover     4443825   4443065   -760    -0.017%
dist      3366078   3365838   -240    -0.007%
doc       3776391   3776615   +224    +0.006%
fix       3218800   3218648   -152    -0.005%
link      6365321   6365345   +24     +0.000%
nm        3923625   3923857   +232    +0.006%
objdump   4295569   4295041   -528    -0.012%
pack      2390745   2389217   -1528   -0.064%
pprof     12870094  12866942  -3152   -0.024%
test2json 2587265   2587073   -192    -0.007%
trace     9612629   9613981   +1352   +0.014%
vet       6791008   6792072   +1064   +0.016%
total     106856682 106850412 -6270   -0.006%

Update #37608

Change-Id: Ic6206b22fd1faf570be9fd3c2511aa6c4ce38cdb
Reviewed-on: https://go-review.googlesource.com/c/go/+/252937
Trust: fannie zhang <Fannie.Zhang@arm.com>
Run-TryBot: fannie zhang <Fannie.Zhang@arm.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

CL 28978 (6ec993a) accidentally disabled the test (it would only
run if amd64 AND s390x, whereas it should be amd64 OR s390x).

Change-Id: I23c1ad71724ff55f5808d5896b19b62c8ec5af76
Reviewed-on: https://go-review.googlesource.com/28981
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

The new SSA backend modifies the ABI slightly: R0 is now a usable
general purpose register.

Fixes #16677.

Change-Id: I367435ce921e0c7e79e021c80cf8ef5d1d1466cf
Reviewed-on: https://go-review.googlesource.com/28978
Run-TryBot: Michael Munday <munday@ca.ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

Introduce OrB, EqB, NeqB, AndB to handle bool operations.

Change-Id: I53e4d5125a8090d5eeb4576db619103f19fff58d
Reviewed-on: https://go-review.googlesource.com/22412
Reviewed-by: Keith Randall <khr@golang.org>

See discussion at [1]. True value must have a fixed non-zero
representation meaning that a && b can be implemented as a & b.

[1] https://groups.google.com/forum/#!topic/golang-dev/xV0vPuFP9Vg

This change helps with m := a && b, but it's more common to see
if a && b { do something } which is not handled.

Change-Id: Ib6f9ff898a0a8c05d12466e2464e4fe781035394
Reviewed-on: https://go-review.googlesource.com/22313
Run-TryBot: Alexandru Moșoi <alexandru@mosoi.ro>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

func f(a, b bool) bool {
          return a || b
}

is now a single instructions (excluding loading and unloading the arguments):
      v10 = ORB <bool> v11 v12 : AX

Change-Id: Iff63399410cb46909f4318ea1c3f45a029f4aa5e
Reviewed-on: https://go-review.googlesource.com/21872
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>

* 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/20090
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Alexandru Moșoi <alexandru@mosoi.ro>
TryBot-Result: Gobot Gobot <gobot@golang.org>