cmd/compile: relax tighten register-pressure heuristic slightly

Sometimes a value has multiple args, but they are the same
dependency. Relax the regalloc heuristic for those.

No measurable compile-time regression according to compilebench,
maybe even a small improvement.

name    old time/op  new time/op  delta
StdCmd   14.4s ± 1%   14.4s ± 1%  -0.39%  (p=0.101 n=11+11)

compilecmp:

linux/amd64:

strconv
strconv.formatBits 1199 -> 1189  (-0.83%)
strconv.formatDecimal 637 -> 631  (-0.94%)

strconv [cmd/compile]
strconv.formatBits 1199 -> 1189  (-0.83%)
strconv.formatDecimal 637 -> 631  (-0.94%)

image
image.NewGray16 286 -> 275  (-3.85%)
image.NewAlpha16 286 -> 275  (-3.85%)

regexp/syntax
regexp/syntax.ranges.Less 150 -> 147  (-2.00%)
regexp/syntax.(*compiler).rune 774 -> 773  (-0.13%)
regexp/syntax.(*ranges).Swap 197 -> 180  (-8.63%)
regexp/syntax.ranges.Swap 146 -> 134  (-8.22%)
regexp/syntax.(*compiler).cap 440 -> 425  (-3.41%)
regexp/syntax.(*compiler).nop 310 -> 297  (-4.19%)
regexp/syntax.(*compiler).compile 5815 -> 5733  (-1.41%)
regexp/syntax.(*ranges).Less 211 -> 197  (-6.64%)

regexp/syntax [cmd/compile]
regexp/syntax.(*compiler).compile 5815 -> 5733  (-1.41%)
regexp/syntax.(*compiler).rune 774 -> 773  (-0.13%)
regexp/syntax.(*compiler).cap 440 -> 425  (-3.41%)
regexp/syntax.(*ranges).Less 211 -> 197  (-6.64%)
regexp/syntax.ranges.Swap 146 -> 134  (-8.22%)
regexp/syntax.(*ranges).Swap 197 -> 180  (-8.63%)
regexp/syntax.(*compiler).nop 310 -> 297  (-4.19%)
regexp/syntax.ranges.Less 150 -> 147  (-2.00%)

crypto/elliptic
crypto/elliptic.(*nistCurve[go.shape.*uint8]).pointFromAffine 1272 -> 1240  (-2.52%)

image/gif
image/gif.(*decoder).readColorTable 652 -> 646  (-0.92%)
image/gif.(*encoder).colorTablesMatch 350 -> 349  (-0.29%)

crypto/internal/cryptotest
crypto/internal/cryptotest.testCipher.func3 1289 -> 1286  (-0.23%)

internal/trace/internal/tracev1
internal/trace/internal/tracev1.(*parser).collectBatchesAndCPUSamples 1352 -> 1338  (-1.04%)

internal/fuzz
internal/fuzz.byteSliceDuplicateBytes 741 -> 718  (-3.10%)

cmd/compile/internal/types
cmd/compile/internal/types.CalcSize 3663 -> 3633  (-0.82%)

cmd/compile/internal/rttype
cmd/compile/internal/rttype.Init 2149 -> 2124  (-1.16%)

cmd/link/internal/loadmacho
cmd/link/internal/loadmacho.macholoadsym 1213 -> 1212  (-0.08%)

cmd/compile/internal/rangefunc
cmd/compile/internal/rangefunc.(*rewriter).checks 5207 -> 5175  (-0.61%)

net/http
net/http.(*http2SettingsFrame).Setting 155 -> 147  (-5.16%)

cmd/compile/internal/rttype [cmd/compile]
cmd/compile/internal/rttype.Init 2149 -> 2124  (-1.16%)

cmd/compile/internal/rangefunc [cmd/compile]
cmd/compile/internal/rangefunc.(*rewriter).checks 5207 -> 5175  (-0.61%)

cmd/link/internal/ld
cmd/link/internal/ld.pefips 3119 -> 3109  (-0.32%)

cmd/vendor/rsc.io/markdown
cmd/vendor/rsc.io/markdown.parseDash 593 -> 587  (-1.01%)

cmd/compile/internal/ssa
cmd/compile/internal/ssa.(*poset).setOrder 3442 -> 3416  (-0.76%)
cmd/compile/internal/ssa.rewriteValuegeneric_OpMul16 2054 -> 2022  (-1.56%)
cmd/compile/internal/ssa.rewriteValuegeneric_OpMul8 2054 -> 2022  (-1.56%)
inserted cmd/compile/internal/ssa.tighten.deferwrap5

cmd/compile/internal/ssa [cmd/compile]
cmd/compile/internal/ssa.rewriteValuegeneric_OpMul8 2054 -> 2022  (-1.56%)
cmd/compile/internal/ssa.rewriteValuegeneric_OpMul16 2054 -> 2022  (-1.56%)
cmd/compile/internal/ssa.tighten.deferwrap4 76 -> 67  (-11.84%)
cmd/compile/internal/ssa.tighten 6746 -> 5082  (-24.67%)
inserted cmd/compile/internal/ssa.tighten.deferwrap5

file                                             before   after    Δ       %
strconv.s                                        49029    49020    -9      -0.018%
strconv [cmd/compile].s                          49029    49020    -9      -0.018%
image.s                                          34963    34941    -22     -0.063%
regexp/syntax.s                                  83017    82860    -157    -0.189%
regexp/syntax [cmd/compile].s                    83017    82860    -157    -0.189%
crypto/elliptic.s                                26848    26816    -32     -0.119%
image/gif.s                                      22840    22833    -7      -0.031%
crypto/internal/cryptotest.s                     63834    63832    -2      -0.003%
internal/trace/internal/tracev1.s                52995    52981    -14     -0.026%
internal/trace.s                                 181396   181412   +16     +0.009%
internal/fuzz.s                                  85526    85503    -23     -0.027%
cmd/internal/obj/s390x.s                         121651   121683   +32     +0.026%
cmd/internal/obj/ppc64.s                         139867   139871   +4      +0.003%
cmd/compile/internal/types.s                     71425    71395    -30     -0.042%
cmd/internal/obj/ppc64 [cmd/compile].s           139952   139956   +4      +0.003%
cmd/internal/obj/s390x [cmd/compile].s           121753   121785   +32     +0.026%
cmd/compile/internal/rttype.s                    10418    10393    -25     -0.240%
cmd/link/internal/loadmacho.s                    23270    23272    +2      +0.009%
cmd/compile/internal/rangefunc.s                 35050    35018    -32     -0.091%
cmd/vendor/github.com/google/pprof/profile.s     148264   148273   +9      +0.006%
net/http.s                                       612895   612910   +15     +0.002%
cmd/compile/internal/rttype [cmd/compile].s      10397    10372    -25     -0.240%
cmd/compile/internal/rangefunc [cmd/compile].s   35681    35649    -32     -0.090%
net/http/cookiejar.s                             28758    28761    +3      +0.010%
cmd/compile/internal/reflectdata.s               86639    86644    +5      +0.006%
cmd/compile/internal/reflectdata [cmd/compile].s 89725    89730    +5      +0.006%
cmd/link/internal/ld.s                           649596   649633   +37     +0.006%
cmd/vendor/rsc.io/markdown.s                     116731   116757   +26     +0.022%
cmd/compile/internal/ssa.s                       3574185  3574642  +457    +0.013%
cmd/compile/internal/ssa [cmd/compile].s         3725364  3723715  -1649   -0.044%
cmd/compile/internal/ssagen.s                    415135   415155   +20     +0.005%
total                                            36475376 36473818 -1558   -0.004%

linux/arm64:

go/printer
go/printer.(*printer).expr1 7152 -> 7168  (+0.22%)

fmt [cmd/compile]
fmt.(*ss).advance 1712 -> 1696  (-0.93%)

crypto/x509
crypto/x509.marshalCertificatePolicies.func1.2.(*Builder).AddASN1ObjectIdentifier.1 changed

internal/fuzz
internal/fuzz.minimizeBytes changed

cmd/internal/obj/arm64
cmd/internal/obj/arm64.bitconEncode changed

math/big [cmd/compile]
math/big.(*Float).Int64 512 -> 528  (+3.12%)
math/big.NewInt changed
math/big.fmtE 720 -> 736  (+2.22%)
math/big.basicSqr changed

cmd/asm/internal/asm
cmd/asm/internal/asm.(*Parser).asmText 1424 -> 1440  (+1.12%)

go/constant [cmd/compile]
go/constant.UnaryOp changed
go/constant.BinaryOp changed

crypto/tls
crypto/tls.prf10 576 -> 560  (-2.78%)

cmd/internal/obj/arm64 [cmd/compile]
cmd/internal/obj/arm64.bitconEncode changed

cmd/vendor/golang.org/x/term
cmd/vendor/golang.org/x/term.(*Terminal).addKeyToLine changed

cmd/compile/internal/ir
cmd/compile/internal/ir.ConstOverflow changed

cmd/vendor/github.com/google/pprof/internal/graph
cmd/vendor/github.com/google/pprof/internal/graph.(*builder).addEdge changed

cmd/compile/internal/ir [cmd/compile]
cmd/compile/internal/ir.ConstOverflow changed

cmd/compile/internal/rttype
cmd/compile/internal/rttype.Init changed

cmd/compile/internal/rttype [cmd/compile]
cmd/compile/internal/rttype.Init changed

cmd/compile/internal/abi [cmd/compile]
cmd/compile/internal/abi.(*ABIParamAssignment).RegisterTypesAndOffsets 1344 -> 1328  (-1.19%)

cmd/vendor/golang.org/x/tools/go/types/typeutil
cmd/vendor/golang.org/x/tools/go/types/typeutil.hasher.hash changed

cmd/vendor/github.com/ianlancetaylor/demangle
cmd/vendor/github.com/ianlancetaylor/demangle.(*rustState).expandPunycode changed

net/http/cookiejar
net/http/cookiejar.adapt changed
net/http/cookiejar.encode changed

cmd/compile/internal/reflectdata
cmd/compile/internal/reflectdata.OldMapType changed

cmd/compile/internal/reflectdata [cmd/compile]
cmd/compile/internal/reflectdata.OldMapType changed

cmd/vendor/github.com/google/pprof/internal/report
cmd/vendor/github.com/google/pprof/internal/report.(*Report).newTrimmedGraph 2336 -> 2368  (+1.37%)

cmd/link/internal/ld
cmd/link/internal/ld.(*relocSymState).relocsym changed

cmd/vendor/rsc.io/markdown
cmd/vendor/rsc.io/markdown.parseDash changed
cmd/vendor/rsc.io/markdown.parseLinkRefDef changed

cmd/trace
main.(*stackMap).profile 912 -> 880  (-3.51%)

cmd/vendor/golang.org/x/tools/go/analysis/passes/tests
cmd/vendor/golang.org/x/tools/go/analysis/passes/tests.checkExampleOutput 832 -> 816  (-1.92%)

cmd/compile/internal/ssa
cmd/compile/internal/ssa.shouldElimIfElse changed
cmd/compile/internal/ssa.storeOrder changed
cmd/compile/internal/ssa.elimIfElse changed
cmd/compile/internal/ssa.tighten 3408 -> 3456  (+1.41%)

cmd/compile/internal/ssa [cmd/compile]
cmd/compile/internal/ssa.storeOrder changed
cmd/compile/internal/ssa.elimIfElse changed
cmd/compile/internal/ssa.shouldElimIfElse changed
cmd/compile/internal/ssa.tighten 4960 -> 4976  (+0.32%)
cmd/compile/internal/ssa.branchelim changed

file                                                     before   after    Δ       %
runtime.s                                                624064   624032   -32     -0.005%
runtime [cmd/compile].s                                  679456   679424   -32     -0.005%
strconv.s                                                48528    48560    +32     +0.066%
strconv [cmd/compile].s                                  48528    48560    +32     +0.066%
index/suffixarray.s                                      41808    41856    +48     +0.115%
fmt.s                                                    72272    72256    -16     -0.022%
math/big.s                                               152992   153024   +32     +0.021%
go/printer.s                                             77680    77696    +16     +0.021%
fmt [cmd/compile].s                                      81760    81744    -16     -0.020%
math/big [cmd/compile].s                                 153040   153072   +32     +0.021%
cmd/asm/internal/asm.s                                   57360    57376    +16     +0.028%
crypto/tls.s                                             354304   354288   -16     -0.005%
cmd/compile/internal/abi [cmd/compile].s                 22752    22736    -16     -0.070%
cmd/vendor/github.com/google/pprof/internal/report.s     67008    67040    +32     +0.048%
cmd/trace.s                                              215040   215008   -32     -0.015%
cmd/vendor/golang.org/x/tools/go/analysis/passes/tests.s 12544    12528    -16     -0.128%
cmd/compile/internal/ssa.s                               3209248  3209296  +48     +0.001%
cmd/compile/internal/ssa [cmd/compile].s                 3319152  3319168  +16     +0.000%
total                                                    33366288 33366416 +128    +0.000%

Change-Id: I8111792c9dd4f927b49a6d5dd90a3fdc3ec26277
Reviewed-on: https://go-review.googlesource.com/c/go/+/666836
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Carlos Amedee <carlos@golang.org>
Reviewed-by: Keith Randall <khr@google.com>

Author: jake-ciolek

src/cmd/compile/internal/ssa/tighten.go

@@ -27,6 +27,8 @@ func tighten(f *Func) {
 	defer f.Cache.freeValueSlice(startMem)
 	endMem := f.Cache.allocValueSlice(f.NumBlocks())
 	defer f.Cache.freeValueSlice(endMem)
+	distinctArgs := f.newSparseSet(f.NumValues())
+	defer f.retSparseSet(distinctArgs)
 	memState(f, startMem, endMem)
 
 	for _, b := range f.Blocks {
@@ -47,16 +49,18 @@ func tighten(f *Func) {
 				// Nil checks need to stay in their block. See issue 72860.
 				continue
 			}
-			// Count arguments which will need a register.
-			narg := 0
+			// Count distinct arguments which will need a register.
+			distinctArgs.clear()
+
 			for _, a := range v.Args {
 				// SP and SB are special registers and have no effect on
 				// the allocation of general-purpose registers.
 				if a.needRegister() && a.Op != OpSB && a.Op != OpSP {
-					narg++
+					distinctArgs.add(a.ID)
 				}
 			}
-			if narg >= 2 && !v.Type.IsFlags() {
+
+			if distinctArgs.size() >= 2 && !v.Type.IsFlags() {
 				// Don't move values with more than one input, as that may
 				// increase register pressure.
 				// We make an exception for flags, as we want flag generators