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Matthew Dempsky 85fc765341 cmd/compile: optimize switch on strings 
When compiling expression switches, we try to optimize runs of
constants into binary searches. The ordering used isn't visible to the
application, so it's unimportant as long as we're consistent between
sorting and searching.

For strings, it's much cheaper to compare string lengths than strings
themselves, so instead of ordering strings by "si <= sj", we currently
order them by "len(si) < len(sj) || len(si) == len(sj) && si <= sj"
(i.e., the lexicographical ordering on the 2-tuple (len(s), s)).

However, it's also somewhat cheaper to compare strings for equality
(i.e., ==) than for ordering (i.e., <=). And if there were two or
three string constants of the same length in a switch statement, we
might unnecessarily emit ordering comparisons.

For example, given:

    switch s {
    case "", "1", "2", "3": // ordered by length then content
        goto L
    }

we currently compile this as:

    if len(s) < 1 || len(s) == 1 && s <= "1" {
        if s == "" { goto L }
        else if s == "1" { goto L }
    } else {
        if s == "2" { goto L }
        else if s == "3" { goto L }
    }

This CL switches to using a 2-level binary search---first on len(s),
then on s itself---so that string ordering comparisons are only needed
when there are 4 or more strings of the same length. (4 being the
cut-off for when using binary search is actually worthwhile.)

So the above switch instead now compiles to:

    if len(s) == 0 {
        if s == "" { goto L }
    } else if len(s) == 1 {
        if s == "1" { goto L }
        else if s == "2" { goto L }
        else if s == "3" { goto L }
    }

which is better optimized by walk and SSA. (Notably, because there are
only two distinct lengths and no more than three strings of any
particular length, this example ends up falling back to simply using
linear search.)

Test case by khr@ from CL 195138.

Fixes #33934.

Change-Id: I8eeebcaf7e26343223be5f443d6a97a0daf84f07
Reviewed-on: https://go-review.googlesource.com/c/go/+/195340
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
2019-09-18 05:33:05 +00:00
..
alias3.dir [dev.typealias] cmd/compile: export/import test cases for type aliases 2017-01-20 05:55:53 +00:00
bench test/bench/go1: add go.mod file 2019-03-06 18:53:12 +00:00
chan test: add a test for gccgo bug in handling break statement in a select 2019-07-10 18:02:11 +00:00
closure3.dir cmd/compile: skip escape analysis diagnostics for OADDR 2019-04-02 16:34:03 +00:00
codegen cmd/compile: optimize switch on strings 2019-09-18 05:33:05 +00:00
ddd2.dir
dwarf
fixedbugs cmd/compile: support more length types for slice extension optimization 2019-09-17 17:18:17 +00:00
import2.dir
import4.dir
interface cmd/compile: more error position tests for the typechecker 2017-04-24 12:37:49 +00:00
intrinsic.dir cmd/compile: intrinsics for math/bits.TrailingZerosX 2017-03-16 02:44:16 +00:00
ken all: fix typos 2019-09-08 17:28:20 +00:00
linkname.dir cmd/compile: trim function name prefix from escape diagnostics 2019-09-16 15:30:51 +00:00
method4.dir
oldescape_linkname.dir cmd/compile: update escape analysis tests for newescape 2019-04-16 16:20:39 +00:00
retjmp.dir cmd/asm: fix assembling return jump 2018-03-01 21:11:16 +00:00
runtime test: remove -newescape from regress tests 2019-08-28 19:27:20 +00:00
stress
syntax cmd/compile: better handling of incorrect type switches 2018-04-03 05:34:20 +00:00
uintptrescapes.dir
64bit.go
235.go
alg.go
alias1.go
alias2.go cmd/compile: cleanup method symbol creation 2018-04-05 22:01:17 +00:00
alias3.go [dev.typealias] cmd/compile: export/import test cases for type aliases 2017-01-20 05:55:53 +00:00
alias.go
align.go test: check that unaligned load-add opcodes work. 2018-04-09 18:57:37 +00:00
append1.go cmd/compile: optimize append(x, make([]T, y)...) slice extension 2018-05-06 04:28:23 +00:00
append.go cmd/compile: optimize append(x, make([]T, y)...) slice extension 2018-05-06 04:28:23 +00:00
args.go
armimm.go cmd/internal/obj: continue to optimize ARM's constant pool 2017-05-11 13:53:54 +00:00
assign1.go
assign.go
atomicload.go
bigalg.go
bigmap.go
blank1.go test: update blank1.go for changed gofrontend error messages 2019-06-23 22:20:39 +00:00
blank.go
bom.go
bombad.go
bounds.go test: gofmt bounds.go 2018-05-29 02:39:16 +00:00
chancap.go runtime: handle 64bits addresses for AIX 2018-11-26 14:06:28 +00:00
chanlinear.go
char_lit1.go
char_lit.go
checkbce.go cmd/compile: fix ordering for short-circuiting ops 2019-03-06 20:04:07 +00:00
clearfat.go
closedchan.go
closure1.go
closure2.go all: fix typos 2019-09-08 17:28:20 +00:00
closure3.go all: fix a bunch of misspellings 2018-10-06 15:40:03 +00:00
closure4.go cmd/compile/internal/gc: add nil check for closure call on wasm 2018-08-14 09:19:38 +00:00
closure.go
cmp6.go
cmp.go
cmplx.go cmd/compile: rewrite f(g()) for multi-value g() during typecheck 2019-03-14 21:00:20 +00:00
cmplxdivide1.go runtime: make complex division c99 compatible 2017-03-15 22:45:17 +00:00
cmplxdivide.c runtime: make complex division c99 compatible 2017-03-15 22:45:17 +00:00
cmplxdivide.go runtime: make complex division c99 compatible 2017-03-15 22:45:17 +00:00
complit1.go cmd/compile: more error position tests for the typechecker 2017-04-24 12:37:49 +00:00
complit.go
compos.go
const1.go cmd/compile: fix ICE from invalid operations on float/complex constants 2019-03-28 17:46:55 +00:00
const2.go
const3.go
const4.go
const5.go
const6.go
const.go cmd/compile: truncate constant arithmetic result with typed complex numbers 2019-08-28 19:45:44 +00:00
convert1.go
convert2.go
convert3.go
convert.go
convlit1.go
convlit.go cmd/compile: rewrite untyped constant conversion logic 2019-09-06 23:15:48 +00:00
convT2X.go
copy1.go cmd/compile: rewrite f(g()) for multi-value g() during typecheck 2019-03-14 21:00:20 +00:00
copy.go
crlf.go
ddd1.go cmd/compile: rewrite untyped constant conversion logic 2019-09-06 23:15:48 +00:00
ddd2.go
ddd.go
decl.go
declbad.go
defer.go
deferfin.go
deferprint.go test: remove rundircmpout and cmpout actions 2018-05-31 17:36:45 +00:00
deferprint.out
devirt.go cmd/compile: de-virtualize interface calls 2017-03-14 18:49:23 +00:00
divide.go
divmod.go
empty.go
env.go
eof1.go
eof.go
escape2.go cmd/compile: trim function name prefix from escape diagnostics 2019-09-16 15:30:51 +00:00
escape2n.go cmd/compile: trim function name prefix from escape diagnostics 2019-09-16 15:30:51 +00:00
escape3.go
escape4.go cmd/compile: skip escape analysis diagnostics for OADDR 2019-04-02 16:34:03 +00:00
escape5.go cmd/compile: silence esc diagnostics about directiface OCONVIFACEs 2019-09-03 17:52:06 +00:00
escape_array.go cmd/compile: trim function name prefix from escape diagnostics 2019-09-16 15:30:51 +00:00
escape_calls.go cmd/compile: trim function name prefix from escape diagnostics 2019-09-16 15:30:51 +00:00
escape_closure.go cmd/compile: trim function name prefix from escape diagnostics 2019-09-16 15:30:51 +00:00
escape_field.go cmd/compile: trim function name prefix from escape diagnostics 2019-09-16 15:30:51 +00:00
escape_goto.go cmd/compile: preserve loop depth when evaluating block 2019-09-06 01:35:46 +00:00
escape_iface.go cmd/compile: trim function name prefix from escape diagnostics 2019-09-16 15:30:51 +00:00
escape_indir.go cmd/compile: trim function name prefix from escape diagnostics 2019-09-16 15:30:51 +00:00
escape_level.go cmd/compile: silence esc diagnostics about directiface OCONVIFACEs 2019-09-03 17:52:06 +00:00
escape_map.go cmd/compile: silence esc diagnostics about directiface OCONVIFACEs 2019-09-03 17:52:06 +00:00
escape_param.go cmd/compile: trim function name prefix from escape diagnostics 2019-09-16 15:30:51 +00:00
escape_runtime_atomic.go test: fix escape_runtime_atomic.go 2019-04-17 22:55:26 +00:00
escape_selfassign.go test: add regress test cases for self-assignment 2019-04-17 16:36:56 +00:00
escape_slice.go cmd/compile: skip escape analysis diagnostics for OADDR 2019-04-02 16:34:03 +00:00
escape_struct_param1.go cmd/compile: trim function name prefix from escape diagnostics 2019-09-16 15:30:51 +00:00
escape_struct_param2.go cmd/compile: trim function name prefix from escape diagnostics 2019-09-16 15:30:51 +00:00
escape_struct_return.go test: remove -newescape from regress tests 2019-08-28 19:27:20 +00:00
escape_sync_atomic.go runtime/internal/atomic: remove bad go:noescape annotations on Loadp 2019-04-17 19:09:15 +00:00
escape_unsafe.go cmd/compile: silence esc diagnostics about directiface OCONVIFACEs 2019-09-03 17:52:06 +00:00
escape.go
fibo.go
finprofiled.go all: fix typos 2019-09-08 17:28:20 +00:00
float_lit2.go
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 all: skip unsupported tests for js/wasm 2018-04-30 19:39:18 +00:00
gc.go
gcgort.go test: fast GC+concurrency+types verification 2018-05-08 21:15:48 +00:00
gcstring.go
goprint.go test: remove rundircmpout and cmpout actions 2018-05-31 17:36:45 +00:00
goprint.out
goto.go cmd/compile: report block start for gotos jumping into blocks 2017-04-19 02:27:58 +00:00
heapsampling.go test: improve test coverage for heap sampling 2019-03-07 21:05:15 +00:00
helloworld.go test: remove rundircmpout and cmpout actions 2018-05-31 17:36:45 +00:00
helloworld.out
if.go
import1.go
import2.go
import4.go
import5.go cmd/compile: be slightly more tolerant in case of certain syntax errors 2017-03-24 20:07:15 +00:00
import6.go cmd/compile/internal/syntax: removed gcCompat code needed to pass orig. tests 2017-02-10 01:22:30 +00:00
import.go
index0.go
index1.go
index2.go
index.go all: fix typos 2019-09-08 17:28:20 +00:00
indirect1.go
indirect.go
init1.go
init.go cmd/compile: reorganize init functions 2019-03-18 20:10:55 +00:00
initcomma.go
initialize.go
initializerr.go cmd/compile: more error position tests for the typechecker 2017-04-24 12:37:49 +00:00
initloop.go
inline_big.go cmd/compile: trim function name prefix from escape diagnostics 2019-09-16 15:30:51 +00:00
inline_caller.go runtime: make FuncForPC return the innermost inlined frame 2019-01-08 21:54:04 +00:00
inline_callers.go runtime: make FuncForPC return the innermost inlined frame 2019-01-08 21:54:04 +00:00
inline_literal.go cmd/compile: copy literals when inlining 2017-03-03 21:29:32 +00:00
inline_math_bits_rotate.go cmd/compile: make math/bits.RotateLeft* an intrinsic on amd64 2018-08-30 22:48:28 +00:00
inline_sync.go cmd/compile: skip escape analysis diagnostics for OADDR 2019-04-02 16:34:03 +00:00
inline_variadic.go cmd/compile: enable inlining variadic functions 2018-03-13 20:34:03 +00:00
inline.go cmd/compile: trim function name prefix from escape diagnostics 2019-09-16 15:30:51 +00:00
int_lit.go
intcvt.go
intrinsic_atomic.go cmd/compile: intrinsify atomics on MIPS64 2017-10-10 19:43:38 +00:00
intrinsic.go
iota.go
label1.go cmd/compile/internal/gc: don't panic on continue in switch 2017-04-12 14:27:45 +00:00
label.go
linkmain_run.go all: skip unsupported tests for js/wasm 2018-04-30 19:39:18 +00:00
linkmain.go
linkname.go test: remove -newescape from regress tests 2019-08-28 19:27:20 +00:00
linkobj.go all: skip unsupported tests for js/wasm 2018-04-30 19:39:18 +00:00
linkx_run.go all: skip unsupported tests for js/wasm 2018-04-30 19:39:18 +00:00
linkx.go
literal2.go cmd/compile: accept 'i' suffix orthogonally on all numbers 2019-02-19 22:45:09 +00:00
literal.go
live1.go
live2.go cmd/compile: extend ssa.go to handle 1-element array and 1-field struct 2019-09-03 19:33:04 +00:00
live_syscall.go cmd/compile: trim function name prefix from escape diagnostics 2019-09-16 15:30:51 +00:00
live.go cmd/compile: extend ssa.go to handle 1-element array and 1-field struct 2019-09-03 19:33:04 +00:00
locklinear.go test: skip locklinear's lockmany test for now 2018-04-05 10:53:40 +00:00
loopbce.go cmd/compile: reverse order of slice bounds checks 2019-03-09 00:52:45 +00:00
makechan.go cmd/compile: generate makechan calls with int arguments 2017-08-15 05:54:24 +00:00
makemap.go test: check that size argument errors are emitted at call site 2018-03-14 08:36:15 +00:00
makenew.go cmd/compile: more error position tests for the typechecker 2017-04-24 12:37:49 +00:00
mallocfin.go
map1.go cmd/compile: more error position tests for the typechecker 2017-04-24 12:37:49 +00:00
map.go
mapclear.go cmd/compile: optimize map-clearing range idiom 2018-05-08 21:15:16 +00:00
maplinear.go
mergemul.go cmd/compile: combine x*n - y*n into (x-y)*n 2017-09-03 14:29:38 +00:00
method1.go
method2.go cmd/compile: add two error position tests for the typechecker 2017-10-12 20:50:20 +00:00
method3.go
method4.go
method5.go
method6.go cmd/compile: add two error position tests for the typechecker 2017-10-12 20:50:20 +00:00
method7.go cmd/compile: fix method expressions with anonymous receivers 2018-04-06 15:39:11 +00:00
method.go
named1.go
named.go
nil.go
nilcheck.go
nilptr2.go test: use a real use function in nilptr2.go 2019-05-11 03:02:33 +00:00
nilptr3.go cmd/compile: fix nilcheck for AIX 2018-11-26 14:13:53 +00:00
nilptr4.go
nilptr5_aix.go test: fix nilptr5 for AIX 2018-11-27 15:36:08 +00:00
nilptr5_wasm.go cmd/compile: fix nilcheck for AIX 2018-11-26 14:13:53 +00:00
nilptr5.go cmd/compile: fix nilcheck for AIX 2018-11-26 14:13:53 +00:00
nilptr_aix.go cmd/compile: fix nilcheck for AIX 2018-11-26 14:13:53 +00:00
nilptr.go cmd/compile: fix nilcheck for AIX 2018-11-26 14:13:53 +00:00
nosplit.go ../test: set GOPATH in nosplit.go 2019-03-12 20:46:29 +00:00
notinheap2.go
notinheap3.go cmd/compile: omit write barriers for slice clears of go:notinheap pointers 2018-12-05 21:54:54 +00:00
notinheap.go cmd/compile: disallow converting string to notinheap slice 2018-11-02 19:53:59 +00:00
nowritebarrier.go cmd/compile: improve coverage of nowritebarrierrec check 2017-10-29 19:36:44 +00:00
nul1.go
opt_branchlikely.go all: fix typos 2019-09-08 17:28:20 +00:00
parentype.go
peano.go all: skip unsupported tests for js/wasm 2018-04-30 19:39:18 +00:00
phiopt.go
print.go test: remove rundircmpout and cmpout actions 2018-05-31 17:36:45 +00:00
print.out cmd/compile: fix print/println when input is uint 2017-09-26 04:08:38 +00:00
printbig.go test: remove rundircmpout and cmpout actions 2018-05-31 17:36:45 +00:00
printbig.out
prove.go cmd/compile: handle sign/zero extensions in prove, via update method 2019-08-27 16:46:34 +00:00
range.go cmd/compile: improve single blank variable handling in walkrange 2017-09-12 05:50:54 +00:00
README.md test: use the version of Go used to run run.go 2018-03-03 19:52:00 +00:00
recover1.go
recover2.go cmd/compile,runtime: generate hash functions only for types which are map keys 2019-09-03 20:41:29 +00:00
recover3.go
recover4.go all: use Fatalf instead of Fatal if format is given 2018-01-10 01:35:45 +00:00
recover5.go cmd/compile: more error position tests for the typechecker 2017-04-24 12:37:49 +00:00
recover.go
reflectmethod1.go
reflectmethod2.go
reflectmethod3.go
reflectmethod4.go
rename1.go cmd/compile: rewrite untyped constant conversion logic 2019-09-06 23:15:48 +00:00
rename.go
reorder2.go
reorder.go cmd/compile: Ensure left-to-right assignment 2017-02-11 21:46:21 +00:00
retjmp.go cmd/asm: fix assembling return jump 2018-03-01 21:11:16 +00:00
return.go
rotate0.go
rotate1.go
rotate2.go
rotate3.go
rotate.go
run.go test/fixedbugs: fix some tests will not be run 2019-05-23 01:39:41 +00:00
rune.go
runtime.go cmd/compile/internal/gc: separate builtin and real runtime packages 2017-03-01 01:06:32 +00:00
shift1.go cmd/compile: rewrite untyped constant conversion logic 2019-09-06 23:15:48 +00:00
shift2.go
sieve.go
sigchld.go test: remove rundircmpout and cmpout actions 2018-05-31 17:36:45 +00:00
sigchld.out
simassign.go
sinit_run.go all: skip unsupported tests for js/wasm 2018-04-30 19:39:18 +00:00
sinit.go cmd/compile: fix static initializer 2018-12-03 16:48:21 +00:00
sizeof.go
slice3.go
slice3err.go
slicecap.go
sliceopt.go cmd/compile: make prove pass use unsatisfiability 2018-03-08 22:25:25 +00:00
solitaire.go
stack.go
stackobj2.go test: stress test for stack objects 2018-10-03 19:54:29 +00:00
stackobj3.go cmd/compile,runtime: remove ambiguously live logic 2018-10-03 19:54:16 +00:00
stackobj.go cmd/compile,runtime: remove ambiguously live logic 2018-10-03 19:54:16 +00:00
strcopy.go test: add test to verify that string copies don't get optimized away 2018-06-12 19:10:34 +00:00
strength.go all: fix typos 2019-09-08 17:28:20 +00:00
string_lit.go
stringrange.go
struct0.go
switch2.go
switch3.go
switch4.go
switch5.go Revert "fmt: fix incorrect format of whole-number floats when using %#v" 2018-10-16 21:54:35 +00:00
switch6.go cmd/compile: improve error for wrong type in switch 2017-02-02 17:36:43 +00:00
switch7.go cmd/compile: make duplicate expr cases readable 2017-05-19 18:11:51 +00:00
switch.go
tinyfin.go
torture.go
turing.go
typecheck.go
typecheckloop.go
typeswitch1.go
typeswitch2.go cmd/compile: move duplicate type-case checking into typecheck 2019-09-11 23:33:11 +00:00
typeswitch2b.go cmd/compile: move duplicate type-case checking into typecheck 2019-09-11 23:33:11 +00:00
typeswitch3.go test: fix spelling of caught be the compiler to caught by the compiler 2018-10-04 00:49:49 +00:00
typeswitch.go
uintptrescapes2.go cmd/compile: better integrate parameter tagging with escape.go 2019-09-10 23:01:30 +00:00
uintptrescapes.go
undef.go
utf.go
varerr.go
varinit.go
writebarrier.go cmd/compile: better write barrier removal when initializing new objects 2019-03-18 21:16:19 +00:00
zerodivide.go test: lock in test for _ assignment evaluation/zerodivide panic 2016-12-23 17:35:24 +00:00

README.md

The test directory contains tests of the Go tool chain and runtime. It includes black box tests, regression tests, and error output tests. They are run as part of all.bash.

To run just these tests, execute:

../bin/go run run.go

Standard library tests should be written as regular Go tests in the appropriate package.

The tool chain and runtime also have regular Go tests in their packages. The main reasons to add a new test to this directory are:

  • it is most naturally expressed using the test runner; or
  • it is also applicable to gccgo and other Go tool chains.