cmd/compile: establish limits of bool to uint8 conversions

Improves bound check elimination for:

func arrayLargeEnough(b bool, a [2]int64) int64 {
    c := byte(0)
    if b {
        c = 1
    }

    // this bound check gets elided
    return a[c]
}

We also detect never true branches like:

func cCanOnlyBe0or1(b bool) byte {
    var c byte
    if b {
        c = 1
    }
    // this statement can never be true so we can elide it
    if c == 2 {
        c = 3
    }

    return c
}

Hits a few times:

crypto/internal/sysrand
crypto/internal/sysrand.Read 357 -> 349  (-2.24%)

testing
testing.(*F).Fuzz.func1.1 837 -> 828  (-1.08%)

image/png
image/png.(*Encoder).Encode 1735 -> 1733  (-0.12%)

vendor/golang.org/x/crypto/cryptobyte
vendor/golang.org/x/crypto/cryptobyte.(*Builder).callContinuation 187 -> 185  (-1.07%)

crypto/internal/sysrand [cmd/compile]
crypto/internal/sysrand.Read 357 -> 349  (-2.24%)

go/parser
go/parser.(*parser).parseType 463 -> 457  (-1.30%)
go/parser.(*parser).embeddedElem 633 -> 626  (-1.11%)
go/parser.(*parser).parseFuncDecl 917 -> 914  (-0.33%)
go/parser.(*parser).parseDotsType 393 -> 391  (-0.51%)
go/parser.(*parser).error 1061 -> 1054  (-0.66%)
go/parser.(*parser).parseTypeName 537 -> 532  (-0.93%)
go/parser.(*parser).parseParamDecl 1478 -> 1451  (-1.83%)
go/parser.(*parser).parseFuncTypeOrLit 498 -> 495  (-0.60%)
go/parser.(*parser).parseValue 375 -> 371  (-1.07%)
go/parser.(*parser).parseElementList 594 -> 593  (-0.17%)
go/parser.(*parser).parseResult 593 -> 583  (-1.69%)
go/parser.(*parser).parseElement 506 -> 504  (-0.40%)
go/parser.(*parser).parseImportSpec 1110 -> 1108  (-0.18%)
go/parser.(*parser).parseStructType 741 -> 735  (-0.81%)
go/parser.(*parser).parseTypeSpec 1054 -> 1048  (-0.57%)
go/parser.(*parser).parseIdentList 625 -> 623  (-0.32%)
go/parser.(*parser).parseOperand 1221 -> 1199  (-1.80%)
go/parser.(*parser).parseIndexOrSliceOrInstance 2713 -> 2694  (-0.70%)
go/parser.(*parser).parseSwitchStmt 1458 -> 1447  (-0.75%)
go/parser.(*parser).parseArrayFieldOrTypeInstance 1865 -> 1861  (-0.21%)
go/parser.(*parser).parseExpr 307 -> 305  (-0.65%)
go/parser.(*parser).parseSelector 427 -> 425  (-0.47%)
go/parser.(*parser).parseTypeInstance 1433 -> 1420  (-0.91%)
go/parser.(*parser).parseCaseClause 629 -> 626  (-0.48%)
go/parser.(*parser).parseParameterList 4212 -> 4189  (-0.55%)
go/parser.(*parser).parsePointerType 393 -> 391  (-0.51%)
go/parser.(*parser).parseFuncType 465 -> 463  (-0.43%)
go/parser.(*parser).parseTypeAssertion 559 -> 557  (-0.36%)
go/parser.(*parser).parseSimpleStmt 2443 -> 2388  (-2.25%)
go/parser.(*parser).parseCallOrConversion 1093 -> 1087  (-0.55%)
go/parser.(*parser).parseForStmt 2168 -> 2159  (-0.42%)
go/parser.(*parser).embeddedTerm 657 -> 649  (-1.22%)
go/parser.(*parser).parseCommClause 1509 -> 1501  (-0.53%)

cmd/internal/objfile
cmd/internal/objfile.(*goobjFile).symbols 5299 -> 5274  (-0.47%)

net
net.initConfVal 378 -> 374  (-1.06%)
net.(*conf).hostLookupOrder 269 -> 267  (-0.74%)
net.(*conf).addrLookupOrder 261 -> 255  (-2.30%)

cmd/internal/obj/loong64
cmd/internal/obj/loong64.(*ctxt0).oplook 1829 -> 1813  (-0.87%)

cmd/internal/obj/mips
cmd/internal/obj/mips.(*ctxt0).oplook 1428 -> 1400  (-1.96%)

go/types
go/types.(*typeWriter).signature 605 -> 601  (-0.66%)
go/types.(*Checker).instantiateSignature 1469 -> 1467  (-0.14%)

go/parser [cmd/compile]
go/parser.(*parser).parseSwitchStmt 1458 -> 1447  (-0.75%)
go/parser.(*parser).parseDotsType 393 -> 391  (-0.51%)
go/parser.(*parser).embeddedElem 633 -> 626  (-1.11%)
go/parser.(*parser).parseTypeAssertion 559 -> 557  (-0.36%)
go/parser.(*parser).parseCommClause 1509 -> 1501  (-0.53%)
go/parser.(*parser).parseCaseClause 629 -> 626  (-0.48%)
go/parser.(*parser).parseImportSpec 1110 -> 1108  (-0.18%)
go/parser.(*parser).parseTypeSpec 1054 -> 1048  (-0.57%)
go/parser.(*parser).parseElementList 594 -> 593  (-0.17%)
go/parser.(*parser).parseParamDecl 1478 -> 1451  (-1.83%)
go/parser.(*parser).parseType 463 -> 457  (-1.30%)
go/parser.(*parser).parseSimpleStmt 2443 -> 2388  (-2.25%)
go/parser.(*parser).parseIdentList 625 -> 623  (-0.32%)
go/parser.(*parser).parseTypeInstance 1433 -> 1420  (-0.91%)
go/parser.(*parser).parseResult 593 -> 583  (-1.69%)
go/parser.(*parser).parseValue 375 -> 371  (-1.07%)
go/parser.(*parser).parseFuncDecl 917 -> 914  (-0.33%)
go/parser.(*parser).error 1061 -> 1054  (-0.66%)
go/parser.(*parser).parseElement 506 -> 504  (-0.40%)
go/parser.(*parser).parseFuncType 465 -> 463  (-0.43%)
go/parser.(*parser).parsePointerType 393 -> 391  (-0.51%)
go/parser.(*parser).parseTypeName 537 -> 532  (-0.93%)
go/parser.(*parser).parseExpr 307 -> 305  (-0.65%)
go/parser.(*parser).parseFuncTypeOrLit 498 -> 495  (-0.60%)
go/parser.(*parser).parseStructType 741 -> 735  (-0.81%)
go/parser.(*parser).parseOperand 1221 -> 1199  (-1.80%)
go/parser.(*parser).parseIndexOrSliceOrInstance 2713 -> 2694  (-0.70%)
go/parser.(*parser).parseForStmt 2168 -> 2159  (-0.42%)
go/parser.(*parser).parseParameterList 4212 -> 4189  (-0.55%)
go/parser.(*parser).parseArrayFieldOrTypeInstance 1865 -> 1861  (-0.21%)
go/parser.(*parser).parseSelector 427 -> 425  (-0.47%)
go/parser.(*parser).parseCallOrConversion 1093 -> 1087  (-0.55%)
go/parser.(*parser).embeddedTerm 657 -> 649  (-1.22%)

crypto/tls
crypto/tls.(*Conn).clientHandshake 3430 -> 3421  (-0.26%)

cmd/internal/obj/mips [cmd/compile]
cmd/internal/obj/mips.(*ctxt0).oplook 1428 -> 1400  (-1.96%)

cmd/internal/obj/loong64 [cmd/compile]
cmd/internal/obj/loong64.(*ctxt0).oplook 1829 -> 1813  (-0.87%)

cmd/compile/internal/types2
cmd/compile/internal/types2.(*typeWriter).signature 605 -> 601  (-0.66%)
cmd/compile/internal/types2.(*Checker).infer 10646 -> 10614  (-0.30%)
cmd/compile/internal/types2.(*Checker).instantiateSignature 1567 -> 1561  (-0.38%)

cmd/compile/internal/types2 [cmd/compile]
cmd/compile/internal/types2.(*Checker).instantiateSignature 1567 -> 1561  (-0.38%)
cmd/compile/internal/types2.(*typeWriter).signature 605 -> 601  (-0.66%)
cmd/compile/internal/types2.(*Checker).infer 10718 -> 10654  (-0.60%)

cmd/vendor/golang.org/x/arch/s390x/s390xasm
cmd/vendor/golang.org/x/arch/s390x/s390xasm.GoSyntax 36778 -> 36682  (-0.26%)

net/http
net/http.(*Client).do 4202 -> 4170  (-0.76%)
net/http.(*http2clientStream).writeRequest 3692 -> 3686  (-0.16%)

cmd/vendor/github.com/ianlancetaylor/demangle
cmd/vendor/github.com/ianlancetaylor/demangle.(*rustState).genericArgs 466 -> 463  (-0.64%)

cmd/compile/internal/devirtualize
cmd/compile/internal/devirtualize.ProfileGuided.func1 1364 -> 1357  (-0.51%)

cmd/compile/internal/inline/interleaved
cmd/compile/internal/inline/interleaved.DevirtualizeAndInlinePackage.func2 533 -> 526  (-1.31%)

cmd/compile/internal/devirtualize [cmd/compile]
cmd/compile/internal/devirtualize.ProfileGuided.func1 1343 -> 1332  (-0.82%)

cmd/compile/internal/inline/interleaved [cmd/compile]
cmd/compile/internal/inline/interleaved.DevirtualizeAndInlinePackage.func2 533 -> 526  (-1.31%)

cmd/link/internal/ld
cmd/link/internal/ld.mustLinkExternal 2739 -> 2674  (-2.37%)

cmd/compile/internal/ssa
cmd/compile/internal/ssa.(*poset).Ordered 391 -> 389  (-0.51%)
cmd/compile/internal/ssa.(*poset).Equal 318 -> 313  (-1.57%)
cmd/compile/internal/ssa.(*poset).Undo 1842 -> 1832  (-0.54%)
cmd/compile/internal/ssa.(*expandState).decomposeAsNecessary 4587 -> 4555  (-0.70%)
cmd/compile/internal/ssa.(*poset).OrderedOrEqual 390 -> 389  (-0.26%)
cmd/compile/internal/ssa.(*poset).NonEqual 613 -> 606  (-1.14%)

cmd/compile/internal/ssa [cmd/compile]
cmd/compile/internal/ssa.(*poset).OrderedOrEqual 368 -> 365  (-0.82%)
cmd/compile/internal/ssa.(*poset).Equal 318 -> 313  (-1.57%)
cmd/compile/internal/ssa.(*expandState).decomposeAsNecessary 4952 -> 4938  (-0.28%)
cmd/compile/internal/ssa.(*poset).NonEqual 613 -> 606  (-1.14%)
cmd/compile/internal/ssa.(*poset).SetEqual 2533 -> 2505  (-1.11%)
cmd/compile/internal/ssa.(*poset).SetNonEqual 785 -> 777  (-1.02%)
cmd/compile/internal/ssa.(*poset).Ordered 370 -> 366  (-1.08%)

cmd/compile/internal/gc [cmd/compile]
cmd/compile/internal/gc.Main.DevirtualizeAndInlinePackage.func2 492 -> 489  (-0.61%)

file                                                    before   after    Δ       %
crypto/internal/sysrand.s                               1553     1545     -8      -0.515%
internal/zstd.s                                         49179    49190    +11     +0.022%
testing.s                                               115197   115188   -9      -0.008%
image/png.s                                             36109    36107    -2      -0.006%
vendor/golang.org/x/crypto/cryptobyte.s                 30980    30978    -2      -0.006%
crypto/internal/sysrand [cmd/compile].s                 1553     1545     -8      -0.515%
go/parser.s                                             112638   112354   -284    -0.252%
cmd/internal/objfile.s                                  49994    49969    -25     -0.050%
net.s                                                   299558   299546   -12     -0.004%
cmd/internal/obj/loong64.s                              71651    71635    -16     -0.022%
cmd/internal/obj/mips.s                                 59681    59653    -28     -0.047%
go/types.s                                              558839   558833   -6      -0.001%
cmd/compile/internal/types.s                            71305    71306    +1      +0.001%
go/parser [cmd/compile].s                               112749   112465   -284    -0.252%
crypto/tls.s                                            388859   388850   -9      -0.002%
cmd/internal/obj/mips [cmd/compile].s                   59792    59764    -28     -0.047%
cmd/internal/obj/loong64 [cmd/compile].s                71762    71746    -16     -0.022%
cmd/compile/internal/types2.s                           540608   540566   -42     -0.008%
cmd/compile/internal/types2 [cmd/compile].s             577428   577354   -74     -0.013%
cmd/vendor/golang.org/x/arch/s390x/s390xasm.s           267664   267568   -96     -0.036%
net/http.s                                              620704   620666   -38     -0.006%
cmd/vendor/github.com/ianlancetaylor/demangle.s         299991   299988   -3      -0.001%
cmd/compile/internal/devirtualize.s                     21452    21445    -7      -0.033%
cmd/compile/internal/inline/interleaved.s               8358     8351     -7      -0.084%
cmd/compile/internal/devirtualize [cmd/compile].s       20994    20983    -11     -0.052%
cmd/compile/internal/inline/interleaved [cmd/compile].s 8328     8321     -7      -0.084%
cmd/link/internal/ld.s                                  641802   641737   -65     -0.010%
cmd/compile/internal/ssa.s                              3552939  3552957  +18     +0.001%
cmd/compile/internal/ssa [cmd/compile].s                3752191  3752197  +6      +0.000%
cmd/compile/internal/ssagen.s                           405780   405786   +6      +0.001%
cmd/compile/internal/ssagen [cmd/compile].s             434472   434496   +24     +0.006%
cmd/compile/internal/gc [cmd/compile].s                 38499    38496    -3      -0.008%
total                                                   36185267 36184243 -1024   -0.003%

Change-Id: I867222b0f907b29d32b2676e55c6b5789ec56511
Reviewed-on: https://go-review.googlesource.com/c/go/+/642716
Reviewed-by: Keith Randall <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>
Reviewed-by: Keith Randall <[email protected]>

Author: jake-ciolek

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

@@ -1653,6 +1653,10 @@ func initLimit(v *Value) limit {
 	case OpCtz8, OpBitLen8:
 		lim = lim.unsignedMax(8)
 
+	// bool to uint8 conversion
+	case OpCvtBoolToUint8:
+		lim = lim.unsignedMax(1)
+
 	// length operations
 	case OpStringLen, OpSliceLen, OpSliceCap:
 		lim = lim.signedMin(0)

test/prove.go

@@ -1712,6 +1712,24 @@ func clampedIdx2(x []int, i int) int {
 	return x[max(min(i, len(x)-1), 0)] // TODO: can't get rid of this bounds check yet
 }
 
+func cvtBoolToUint8Disprove(b bool) byte {
+	var c byte
+	if b {
+		c = 1
+	}
+	if c == 2 { // ERROR "Disproved Eq8"
+		c = 3
+	}
+	return c
+}
+func cvtBoolToUint8BCE(b bool, a [2]int64) int64 {
+	c := byte(0)
+	if b {
+		c = 1
+	}
+	return a[c] // ERROR "Proved IsInBounds$"
+}
+
 //go:noinline
 func useInt(a int) {
 }