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
chan
ddd2.dir
dwarf
fixedbugs	cmd/compile: emit assignments after calls in the right order	2016-10-27 16:52:30 +00:00
import2.dir
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
method4.dir
safe
stress
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
alias1.go
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
append.go
args.go
assign1.go
assign.go
atomicload.go
bigalg.go
bigmap.go
blank1.go
blank.go
bom.go
bombad.go
bounds.go
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
cmplxdivide.go
complit1.go
complit.go
compos.go
const1.go
const2.go
const3.go
const4.go
const5.go
const6.go
const.go	cmd/compile: fix compiler bug for constant equality comparison	2016-09-17 01:12:24 +00:00
convert1.go
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
ddd2.go
ddd.go
decl.go
declbad.go
defer.go
deferfin.go
deferprint.go
deferprint.out
divide.go
divmod.go
empty.go
env.go
eof1.go
eof.go
errchk	cmd/vet: make checking example names in _test packages more robust	2016-06-28 22:09:00 +00:00
escape2.go
escape2n.go
escape3.go
escape4.go
escape5.go
escape_array.go
escape_because.go	cmd/compile: add explicit 'where' to EscStep data for explanations	2016-10-26 18:46:59 +00:00
escape_calls.go
escape_closure.go
escape_field.go
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
escape_level.go
escape_map.go
escape_param.go
escape_slice.go
escape_struct_param1.go
escape_struct_param2.go
escape_struct_return.go
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
float_lit.go
floatcmp.go
for.go
func1.go
func2.go
func3.go
func4.go
func5.go
func6.go
func7.go
func8.go
func.go
funcdup2.go
funcdup.go
gc1.go
gc2.go
gc.go
gcstring.go
goprint.go
goprint.out
goto.go
heapsampling.go
helloworld.go
helloworld.out
if.go
import1.go
import2.go
import4.go
import5.go
import.go
index0.go
index1.go
index2.go
index.go
indirect1.go
indirect.go
init1.go
init.go
initcomma.go
initialize.go
initializerr.go
initloop.go
inline.go
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
label.go
linkmain_run.go
linkmain.go
linkobj.go
linkx_run.go
linkx.go
literal.go
live1.go
live2.go	test: re-enable live2 test on amd64	2016-10-07 17:34:02 +00:00
live_syscall.go
live.go	cmd/compile,runtime: redo how map assignments work	2016-10-12 20:41:23 +00:00
loopbce.go
mallocfin.go
map1.go
map.go
maplinear.go
method1.go
method2.go	test: avoid matching file names in errcheck	2016-10-18 05:32:37 +00:00
method3.go
method4.go
method5.go
method.go
named1.go
named.go
nil.go
nilcheck.go
nilptr2.go
nilptr3.go	cmd/compile: re-enable nilcheck removal for newobject	2016-09-28 19:41:49 +00:00
nilptr4.go
nilptr.go
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
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
recover2.go
recover3.go
recover4.go
recover.go
reflectmethod1.go
reflectmethod2.go
reflectmethod3.go
reflectmethod4.go
rename1.go
rename.go
reorder2.go
reorder.go
return.go
rotate0.go
rotate1.go
rotate2.go
rotate3.go
rotate.go
run.go	test: delete bugs directory	2016-10-25 00:17:57 +00:00
rune.go
runtime.go
shift1.go
shift2.go
sieve.go
sigchld.go
sigchld.out
simassign.go
sinit_run.go
sinit.go
sizeof.go
slice3.go
slice3err.go
slicecap.go
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
string_lit.go
stringrange.go
struct0.go
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
utf.go
varerr.go
varinit.go
writebarrier.go	cmd/compile: add a writebarrier phase in SSA	2016-10-25 21:53:40 +00:00
zerodivide.go