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Keith Randall deb4177cf0 cmd/compile: use masks instead of branches for slicing 
When we do

  var x []byte = ...
  y := x[i:]

We can't just use y.ptr = x.ptr + i, as the new pointer may point to the
next object in memory after the backing array.
We used to fix this by doing:

  y.cap = x.cap - i
  delta := i
  if y.cap == 0 {
    delta = 0
  }
  y.ptr = x.ptr + delta

That generates a branch in what is otherwise straight-line code.

Better to do:

  y.cap = x.cap - i
  mask := (y.cap - 1) >> 63 // -1 if y.cap==0, 0 otherwise
  y.ptr = x.ptr + i &^ mask

It's about the same number of instructions (~4, depending on what
parts are constant, and the target architecture), but it is all
inline. It plays nicely with CSE, and the mask can be computed
in parallel with the index (in cases where a multiply is required).

It is a minor win in both speed and space.

Change-Id: Ied60465a0b8abb683c02208402e5bb7ac0e8370f
Reviewed-on: https://go-review.googlesource.com/32022
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
2016-10-27 20:22:49 +00:00
..
alias3.dir cmd/compile: import/export of alias declarations 2016-10-27 17:44:45 +00:00
bench all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
chan all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
ddd2.dir all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
dwarf
fixedbugs cmd/compile: emit assignments after calls in the right order 2016-10-27 16:52:30 +00:00
import2.dir all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
import4.dir
interface cmd/compile: inline x, ok := y.(T) where T is a scalar 2016-08-17 01:12:01 +00:00
intrinsic.dir cmd/compile: intrinsify Ctz, Bswap on ARM 2016-09-12 19:26:31 +00:00
ken all: fix spelling mistakes 2016-04-03 17:03:15 +00:00
method4.dir
safe
stress all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
syntax cmd/compile/internal/gc: enable new parser by default 2016-10-25 22:28:40 +00:00
uintptrescapes.dir cmd/compile, syscall: add //go:uintptrescapes comment, and use it 2016-07-06 20:48:41 +00:00
64bit.go
235.go
alg.go test: add test that required algs get generated 2016-04-24 21:36:52 +00:00
alias1.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
alias2.go cmd/compile: disallow "init" as alias 2016-10-27 20:01:20 +00:00
alias3.go cmd/compile: import/export of alias declarations 2016-10-27 17:44:45 +00:00
alias.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
append.go
args.go
assign1.go
assign.go
atomicload.go cmd/compile: keep value use counts in SSA 2016-03-17 04:20:02 +00:00
bigalg.go
bigmap.go
blank1.go
blank.go
bom.go
bombad.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
bounds.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
chancap.go
chanlinear.go
char_lit1.go
char_lit.go
checkbce.go cmd/compile: optimize integer "in range" expressions 2016-08-25 03:49:16 +00:00
clearfat.go
closedchan.go
closure1.go
closure2.go
closure.go
cmp6.go
cmp.go
cmplx.go
cmplxdivide1.go
cmplxdivide.c all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
cmplxdivide.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
complit1.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
complit.go
compos.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
const1.go
const2.go
const3.go
const4.go
const5.go
const6.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
const.go cmd/compile: fix compiler bug for constant equality comparison 2016-09-17 01:12:24 +00:00
convert1.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
convert2.go cmd/compile: ignore struct tags when converting structs 2016-10-04 17:10:47 +00:00
convert3.go
convert.go
convlit1.go
convlit.go
convT2X.go
copy.go
crlf.go
ddd1.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
ddd2.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
ddd.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
decl.go
declbad.go
defer.go
deferfin.go
deferprint.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
deferprint.out
divide.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
divmod.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
empty.go
env.go
eof1.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
eof.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
errchk cmd/vet: make checking example names in _test packages more robust 2016-06-28 22:09:00 +00:00
escape2.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
escape2n.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
escape3.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
escape4.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
escape5.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
escape_array.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
escape_because.go cmd/compile: add explicit 'where' to EscStep data for explanations 2016-10-26 18:46:59 +00:00
escape_calls.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
escape_closure.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
escape_field.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
escape_iface.go cmd/compile: avoid leak of dottype expression on double assignment form 2016-10-10 12:09:16 +00:00
escape_indir.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
escape_level.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
escape_map.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
escape_param.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
escape_slice.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
escape_struct_param1.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
escape_struct_param2.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
escape_struct_return.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
escape.go
fibo.go
finprofiled.go
float_lit2.go test/float_lit2: fix expressions in comment 2016-09-14 16:39:47 +00:00
float_lit3.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
float_lit.go
floatcmp.go
for.go
func1.go
func2.go
func3.go
func4.go
func5.go
func6.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
func7.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
func8.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
func.go
funcdup2.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
funcdup.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
gc1.go
gc2.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
gc.go
gcstring.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
goprint.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
goprint.out
goto.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
heapsampling.go
helloworld.go
helloworld.out
if.go
import1.go
import2.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
import4.go
import5.go
import.go
index0.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
index1.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
index2.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
index.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
indirect1.go
indirect.go
init1.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
init.go
initcomma.go
initialize.go
initializerr.go
initloop.go
inline.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
int_lit.go
intcvt.go
intrinsic_atomic.go cmd/compile: intrinsify Ctz, Bswap on ARM 2016-09-12 19:26:31 +00:00
intrinsic.go cmd/compile: intrinsify Ctz{32,64} and Bswap{32,64} on s390x 2016-09-19 19:03:01 +00:00
iota.go
label1.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
label.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
linkmain_run.go
linkmain.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
linkobj.go cmd/compile: add -linkobj flag to allow writing object file in two parts 2016-05-09 17:31:45 +00:00
linkx_run.go test: print output on link -X failure 2016-04-20 17:37:35 +00:00
linkx.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
literal.go
live1.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
live2.go test: re-enable live2 test on amd64 2016-10-07 17:34:02 +00:00
live_syscall.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
live.go cmd/compile,runtime: redo how map assignments work 2016-10-12 20:41:23 +00:00
loopbce.go cmd/compile: bce when max and limit are consts 2016-04-11 16:01:22 +00:00
mallocfin.go
map1.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
map.go
maplinear.go
method1.go cmd/compile: ignore receiver parameters in Eqtype 2016-03-17 00:38:15 +00:00
method2.go test: avoid matching file names in errcheck 2016-10-18 05:32:37 +00:00
method3.go
method4.go
method5.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
method.go
named1.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
named.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
nil.go
nilcheck.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
nilptr2.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
nilptr3.go cmd/compile: re-enable nilcheck removal for newobject 2016-09-28 19:41:49 +00:00
nilptr4.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
nilptr.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
nosplit.go cmd/compile: ppc64le working, not optimized enough 2016-08-18 16:34:47 +00:00
notinheap2.go cmd/compile: add go:notinheap type pragma 2016-10-15 17:58:14 +00:00
notinheap.go cmd/compile: add go:notinheap type pragma 2016-10-15 17:58:14 +00:00
nowritebarrier.go cmd/compile, runtime: add go:yeswritebarrierrec pragma 2016-10-15 17:58:11 +00:00
nul1.go cmd/compile/internal/gc: enable new parser by default 2016-10-25 22:28:40 +00:00
opt_branchlikely.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
parentype.go
peano.go
phiopt.go test: re-enable phi optimization test 2016-09-13 20:06:13 +00:00
print.go
print.out
printbig.go
printbig.out
prove.go cmd/compile: Repurpose old sliceopt.go for prove phase. 2016-10-20 23:50:19 +00:00
range.go
recover1.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
recover2.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
recover3.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
recover4.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
recover.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
reflectmethod1.go cmd/compile: track reflect.Type.Method in deadcode 2016-03-11 21:19:20 +00:00
reflectmethod2.go cmd/compile: track reflect.Type.Method in deadcode 2016-03-11 21:19:20 +00:00
reflectmethod3.go cmd/compile: track reflect.Type.Method in deadcode 2016-03-11 21:19:20 +00:00
reflectmethod4.go cmd/link: treat reflect.Value.Method like Call 2016-03-11 22:07:02 +00:00
rename1.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
rename.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
reorder2.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
reorder.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
return.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
rotate0.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
rotate1.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
rotate2.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
rotate3.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
rotate.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
run.go test: delete bugs directory 2016-10-25 00:17:57 +00:00
rune.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
runtime.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
shift1.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
shift2.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
sieve.go
sigchld.go
sigchld.out
simassign.go
sinit_run.go
sinit.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
sizeof.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
slice3.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
slice3err.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
slicecap.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
sliceopt.go cmd/compile: use masks instead of branches for slicing 2016-10-27 20:22:49 +00:00
solitaire.go
stack.go
strength.go cmd/compile: generalize strength reduction of mulq 2016-03-30 22:27:13 +00:00
string_lit.go
stringrange.go
struct0.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
switch2.go cmd/compile/internal/syntax: match old parser errors and line numbers 2016-08-19 01:10:21 +00:00
switch3.go
switch4.go
switch5.go cmd/compile: fix detection of duplicate cases for integer ranges 2016-10-21 22:55:28 +00:00
switch6.go cmd/compile: set correct line number for multiple defaults in switch error 2016-08-22 19:56:06 +00:00
switch.go
tinyfin.go
torture.go
turing.go
typecheck.go
typecheckloop.go
typeswitch1.go
typeswitch2.go
typeswitch3.go
typeswitch.go
uintptrescapes2.go cmd/compile: args no longer live until end-of-function 2016-09-19 16:54:35 +00:00
uintptrescapes.go cmd/compile, syscall: add //go:uintptrescapes comment, and use it 2016-07-06 20:48:41 +00:00
undef.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
utf.go
varerr.go all: make copyright headers consistent with one space after period 2016-05-02 13:43:18 +00:00
varinit.go
writebarrier.go cmd/compile: add a writebarrier phase in SSA 2016-10-25 21:53:40 +00:00
zerodivide.go