cmd/compile: intrinsify math/bits.Add on amd64

name             old time/op  new time/op  delta
Add-8            1.11ns ± 0%  1.18ns ± 0%   +6.31%  (p=0.029 n=4+4)
Add32-8          1.02ns ± 0%  1.02ns ± 1%     ~     (p=0.333 n=4+5)
Add64-8          1.11ns ± 1%  1.17ns ± 0%   +5.79%  (p=0.008 n=5+5)
Add64multiple-8  4.35ns ± 1%  0.86ns ± 0%  -80.22%  (p=0.000 n=5+4)

The individual ops are a bit slower (but still very fast).
Using the ops in carry chains is very fast.

Update #28273

Change-Id: Id975f76df2b930abf0e412911d327b6c5b1befe5
Reviewed-on: https://go-review.googlesource.com/c/144257
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

src/cmd/compile/internal/amd64/ssa.go

@@ -360,6 +360,34 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
 		p.To.Type = obj.TYPE_REG
 		p.To.Reg = r
 
+	case ssa.OpAMD64ADDQcarry, ssa.OpAMD64ADCQ:
+		r := v.Reg0()
+		r0 := v.Args[0].Reg()
+		r1 := v.Args[1].Reg()
+		switch r {
+		case r0:
+			p := s.Prog(v.Op.Asm())
+			p.From.Type = obj.TYPE_REG
+			p.From.Reg = r1
+			p.To.Type = obj.TYPE_REG
+			p.To.Reg = r
+		case r1:
+			p := s.Prog(v.Op.Asm())
+			p.From.Type = obj.TYPE_REG
+			p.From.Reg = r0
+			p.To.Type = obj.TYPE_REG
+			p.To.Reg = r
+		default:
+			v.Fatalf("output not in same register as an input %s", v.LongString())
+		}
+
+	case ssa.OpAMD64ADDQconstcarry, ssa.OpAMD64ADCQconst:
+		p := s.Prog(v.Op.Asm())
+		p.From.Type = obj.TYPE_CONST
+		p.From.Offset = v.AuxInt
+		p.To.Type = obj.TYPE_REG
+		p.To.Reg = v.Reg0()
+
 	case ssa.OpAMD64ADDQconst, ssa.OpAMD64ADDLconst:
 		r := v.Reg()
 		a := v.Args[0].Reg()
@@ -946,6 +974,16 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
 		p := s.Prog(v.Op.Asm())
 		p.To.Type = obj.TYPE_REG
 		p.To.Reg = r
+
+	case ssa.OpAMD64NEGLflags:
+		r := v.Reg0()
+		if r != v.Args[0].Reg() {
+			v.Fatalf("input[0] and output not in same register %s", v.LongString())
+		}
+		p := s.Prog(v.Op.Asm())
+		p.To.Type = obj.TYPE_REG
+		p.To.Reg = r
+
 	case ssa.OpAMD64BSFQ, ssa.OpAMD64BSRQ, ssa.OpAMD64BSFL, ssa.OpAMD64BSRL, ssa.OpAMD64SQRTSD:
 		p := s.Prog(v.Op.Asm())
 		p.From.Type = obj.TYPE_REG

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

@@ -3481,6 +3481,13 @@ func init() {
 		},
 		sys.AMD64, sys.ARM64, sys.PPC64)
 
+	addF("math/bits", "Add64",
+		func(s *state, n *Node, args []*ssa.Value) *ssa.Value {
+			return s.newValue3(ssa.OpAdd64carry, types.NewTuple(types.Types[TUINT64], types.Types[TUINT64]), args[0], args[1], args[2])
+		},
+		sys.AMD64)
+	alias("math/bits", "Add", "math/bits", "Add64", sys.ArchAMD64)
+
 	/******** sync/atomic ********/
 
 	// Note: these are disabled by flag_race in findIntrinsic below.

src/cmd/compile/internal/ssa/gen/AMD64.rules

@@ -29,6 +29,19 @@
 (Div8u x y) -> (Select0 (DIVWU (ZeroExt8to16 x) (ZeroExt8to16 y)))
 (Div(32|64)F x y) -> (DIVS(S|D) x y)
 
+(Select0 (Add64carry x y c)) ->
+	(Select0 <typ.UInt64> (ADCQ x y (Select1 <types.TypeFlags> (NEGLflags c))))
+(Select1 (Add64carry x y c)) ->
+	(NEGQ <typ.UInt64> (SBBQcarrymask <typ.UInt64> (Select1 <types.TypeFlags> (ADCQ x y (Select1 <types.TypeFlags> (NEGLflags c))))))
+
+// Optimize ADCQ and friends
+(ADCQ x (MOVQconst [c]) carry) && is32Bit(c) -> (ADCQconst x [c] carry)
+(ADCQ x y (FlagEQ)) -> (ADDQcarry x y)
+(ADCQconst x [c] (FlagEQ)) -> (ADDQconstcarry x [c])
+(ADDQcarry x (MOVQconst [c])) && is32Bit(c) -> (ADDQconstcarry x [c])
+(Select1 (NEGLflags (MOVQconst [0]))) -> (FlagEQ)
+(Select1 (NEGLflags (NEGQ (SBBQcarrymask x)))) -> x
+
 (Mul64uhilo x y) -> (MULQU2 x y)
 (Div128u xhi xlo y) -> (DIVQU2 xhi xlo y)
 

src/cmd/compile/internal/ssa/gen/AMD64Ops.go

@@ -107,16 +107,18 @@ func init() {
 
 	// Common regInfo
 	var (
-		gp01      = regInfo{inputs: nil, outputs: gponly}
+		gp01           = regInfo{inputs: nil, outputs: gponly}
-		gp11      = regInfo{inputs: []regMask{gp}, outputs: gponly}
+		gp11           = regInfo{inputs: []regMask{gp}, outputs: gponly}
-		gp11sp    = regInfo{inputs: []regMask{gpsp}, outputs: gponly}
+		gp11sp         = regInfo{inputs: []regMask{gpsp}, outputs: gponly}
-		gp11sb    = regInfo{inputs: []regMask{gpspsb}, outputs: gponly}
+		gp11sb         = regInfo{inputs: []regMask{gpspsb}, outputs: gponly}
-		gp21      = regInfo{inputs: []regMask{gp, gp}, outputs: gponly}
+		gp21           = regInfo{inputs: []regMask{gp, gp}, outputs: gponly}
-		gp21sp    = regInfo{inputs: []regMask{gpsp, gp}, outputs: gponly}
+		gp21sp         = regInfo{inputs: []regMask{gpsp, gp}, outputs: gponly}
-		gp21sb    = regInfo{inputs: []regMask{gpspsb, gpsp}, outputs: gponly}
+		gp21sb         = regInfo{inputs: []regMask{gpspsb, gpsp}, outputs: gponly}
-		gp21shift = regInfo{inputs: []regMask{gp, cx}, outputs: []regMask{gp}}
+		gp21shift      = regInfo{inputs: []regMask{gp, cx}, outputs: []regMask{gp}}
-		gp11div   = regInfo{inputs: []regMask{ax, gpsp &^ dx}, outputs: []regMask{ax, dx}}
+		gp11div        = regInfo{inputs: []regMask{ax, gpsp &^ dx}, outputs: []regMask{ax, dx}}
-		gp21hmul  = regInfo{inputs: []regMask{ax, gpsp}, outputs: []regMask{dx}, clobbers: ax}
+		gp21hmul       = regInfo{inputs: []regMask{ax, gpsp}, outputs: []regMask{dx}, clobbers: ax}
+		gp21flags      = regInfo{inputs: []regMask{gp, gp}, outputs: []regMask{gp, 0}}
+		gp2flags1flags = regInfo{inputs: []regMask{gp, gp, 0}, outputs: []regMask{gp, 0}}
 
 		gp2flags     = regInfo{inputs: []regMask{gpsp, gpsp}}
 		gp1flags     = regInfo{inputs: []regMask{gpsp}}
@@ -124,7 +126,8 @@ func init() {
 		gp1flagsLoad = regInfo{inputs: []regMask{gpspsb, gpsp, 0}}
 		flagsgp      = regInfo{inputs: nil, outputs: gponly}
 
-		gp11flags = regInfo{inputs: []regMask{gp}, outputs: []regMask{gp, 0}}
+		gp11flags      = regInfo{inputs: []regMask{gp}, outputs: []regMask{gp, 0}}
+		gp1flags1flags = regInfo{inputs: []regMask{gp, 0}, outputs: []regMask{gp, 0}}
 
 		readflags = regInfo{inputs: nil, outputs: gponly}
 		flagsgpax = regInfo{inputs: nil, clobbers: ax, outputs: []regMask{gp &^ ax}}
@@ -229,6 +232,13 @@ func init() {
 		{name: "DIVLU", argLength: 2, reg: gp11div, typ: "(UInt32,UInt32)", asm: "DIVL", clobberFlags: true}, // [arg0 / arg1, arg0 % arg1]
 		{name: "DIVWU", argLength: 2, reg: gp11div, typ: "(UInt16,UInt16)", asm: "DIVW", clobberFlags: true}, // [arg0 / arg1, arg0 % arg1]
 
+		{name: "NEGLflags", argLength: 1, reg: gp11flags, typ: "(UInt32,Flags)", asm: "NEGL", resultInArg0: true}, // -arg0, flags set for 0-arg0.
+		// The following 4 add opcodes return the low 64 bits of the sum in the first result and
+		// the carry (the 65th bit) in the carry flag.
+		{name: "ADDQcarry", argLength: 2, reg: gp21flags, typ: "(UInt64,Flags)", asm: "ADDQ", commutative: true, resultInArg0: true},                              // r = arg0+arg1
+		{name: "ADCQ", argLength: 3, reg: gp2flags1flags, typ: "(UInt64,Flags)", asm: "ADCQ", commutative: true, resultInArg0: true},                              // r = arg0+arg1+carry(arg2)
+		{name: "ADDQconstcarry", argLength: 1, reg: gp11flags, typ: "(UInt64,Flags)", asm: "ADDQ", aux: "Int32", resultInArg0: true},                              // r = arg0+auxint
+		{name: "ADCQconst", argLength: 2, reg: gp1flags1flags, typ: "(UInt64,Flags)", asm: "ADCQ", aux: "Int32", resultInArg0: true},                              // r = arg0+auxint+carry(arg1)
 		{name: "MULQU2", argLength: 2, reg: regInfo{inputs: []regMask{ax, gpsp}, outputs: []regMask{dx, ax}}, commutative: true, asm: "MULQ", clobberFlags: true}, // arg0 * arg1, returns (hi, lo)
 		{name: "DIVQU2", argLength: 3, reg: regInfo{inputs: []regMask{dx, ax, gpsp}, outputs: []regMask{ax, dx}}, asm: "DIVQ", clobberFlags: true},                // arg0:arg1 / arg2 (128-bit divided by 64-bit), returns (q, r)
 

src/cmd/compile/internal/ssa/gen/genericOps.go

@@ -491,6 +491,8 @@ var genericOps = []opData{
 	{name: "Sub32carry", argLength: 2, typ: "(UInt32,Flags)"}, // arg0 - arg1, returns (value, carry)
 	{name: "Sub32withcarry", argLength: 3},                    // arg0 - arg1 - arg2, arg2=carry (0 or 1)
 
+	{name: "Add64carry", argLength: 3, commutative: true, typ: "(UInt64,UInt64)"}, // arg0 + arg1 + arg2, arg2 must be 0 or 1. returns (value, value>>64)
+
 	{name: "Signmask", argLength: 1, typ: "Int32"},  // 0 if arg0 >= 0, -1 if arg0 < 0
 	{name: "Zeromask", argLength: 1, typ: "UInt32"}, // 0 if arg0 == 0, 0xffffffff if arg0 != 0
 	{name: "Slicemask", argLength: 1},               // 0 if arg0 == 0, -1 if arg0 > 0, undef if arg0<0. Type is native int size.

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

@@ -523,6 +523,11 @@ const (
 	OpAMD64DIVQU
 	OpAMD64DIVLU
 	OpAMD64DIVWU
+	OpAMD64NEGLflags
+	OpAMD64ADDQcarry
+	OpAMD64ADCQ
+	OpAMD64ADDQconstcarry
+	OpAMD64ADCQconst
 	OpAMD64MULQU2
 	OpAMD64DIVQU2
 	OpAMD64ANDQ
@@ -2393,6 +2398,7 @@ const (
 	OpAdd32withcarry
 	OpSub32carry
 	OpSub32withcarry
+	OpAdd64carry
 	OpSignmask
 	OpZeromask
 	OpSlicemask
@@ -6540,6 +6546,87 @@ var opcodeTable = [...]opInfo{
 			},
 		},
 	},
+	{
+		name:         "NEGLflags",
+		argLen:       1,
+		resultInArg0: true,
+		asm:          x86.ANEGL,
+		reg: regInfo{
+			inputs: []inputInfo{
+				{0, 65519}, // AX CX DX BX BP SI DI R8 R9 R10 R11 R12 R13 R14 R15
+			},
+			outputs: []outputInfo{
+				{1, 0},
+				{0, 65519}, // AX CX DX BX BP SI DI R8 R9 R10 R11 R12 R13 R14 R15
+			},
+		},
+	},
+	{
+		name:         "ADDQcarry",
+		argLen:       2,
+		commutative:  true,
+		resultInArg0: true,
+		asm:          x86.AADDQ,
+		reg: regInfo{
+			inputs: []inputInfo{
+				{0, 65519}, // AX CX DX BX BP SI DI R8 R9 R10 R11 R12 R13 R14 R15
+				{1, 65519}, // AX CX DX BX BP SI DI R8 R9 R10 R11 R12 R13 R14 R15
+			},
+			outputs: []outputInfo{
+				{1, 0},
+				{0, 65519}, // AX CX DX BX BP SI DI R8 R9 R10 R11 R12 R13 R14 R15
+			},
+		},
+	},
+	{
+		name:         "ADCQ",
+		argLen:       3,
+		commutative:  true,
+		resultInArg0: true,
+		asm:          x86.AADCQ,
+		reg: regInfo{
+			inputs: []inputInfo{
+				{0, 65519}, // AX CX DX BX BP SI DI R8 R9 R10 R11 R12 R13 R14 R15
+				{1, 65519}, // AX CX DX BX BP SI DI R8 R9 R10 R11 R12 R13 R14 R15
+			},
+			outputs: []outputInfo{
+				{1, 0},
+				{0, 65519}, // AX CX DX BX BP SI DI R8 R9 R10 R11 R12 R13 R14 R15
+			},
+		},
+	},
+	{
+		name:         "ADDQconstcarry",
+		auxType:      auxInt32,
+		argLen:       1,
+		resultInArg0: true,
+		asm:          x86.AADDQ,
+		reg: regInfo{
+			inputs: []inputInfo{
+				{0, 65519}, // AX CX DX BX BP SI DI R8 R9 R10 R11 R12 R13 R14 R15
+			},
+			outputs: []outputInfo{
+				{1, 0},
+				{0, 65519}, // AX CX DX BX BP SI DI R8 R9 R10 R11 R12 R13 R14 R15
+			},
+		},
+	},
+	{
+		name:         "ADCQconst",
+		auxType:      auxInt32,
+		argLen:       2,
+		resultInArg0: true,
+		asm:          x86.AADCQ,
+		reg: regInfo{
+			inputs: []inputInfo{
+				{0, 65519}, // AX CX DX BX BP SI DI R8 R9 R10 R11 R12 R13 R14 R15
+			},
+			outputs: []outputInfo{
+				{1, 0},
+				{0, 65519}, // AX CX DX BX BP SI DI R8 R9 R10 R11 R12 R13 R14 R15
+			},
+		},
+	},
 	{
 		name:         "MULQU2",
 		argLen:       2,
@@ -29629,6 +29716,12 @@ var opcodeTable = [...]opInfo{
 		argLen:  3,
 		generic: true,
 	},
+	{
+		name:        "Add64carry",
+		argLen:      3,
+		commutative: true,
+		generic:     true,
+	},
 	{
 		name:    "Signmask",
 		argLen:  1,

src/cmd/compile/internal/ssa/rewriteAMD64.go

@@ -15,6 +15,10 @@ var _ = types.TypeMem // in case not otherwise used
 
 func rewriteValueAMD64(v *Value) bool {
 	switch v.Op {
+	case OpAMD64ADCQ:
+		return rewriteValueAMD64_OpAMD64ADCQ_0(v)
+	case OpAMD64ADCQconst:
+		return rewriteValueAMD64_OpAMD64ADCQconst_0(v)
 	case OpAMD64ADDL:
 		return rewriteValueAMD64_OpAMD64ADDL_0(v) || rewriteValueAMD64_OpAMD64ADDL_10(v) || rewriteValueAMD64_OpAMD64ADDL_20(v)
 	case OpAMD64ADDLconst:
@@ -27,6 +31,8 @@ func rewriteValueAMD64(v *Value) bool {
 		return rewriteValueAMD64_OpAMD64ADDLmodify_0(v)
 	case OpAMD64ADDQ:
 		return rewriteValueAMD64_OpAMD64ADDQ_0(v) || rewriteValueAMD64_OpAMD64ADDQ_10(v) || rewriteValueAMD64_OpAMD64ADDQ_20(v)
+	case OpAMD64ADDQcarry:
+		return rewriteValueAMD64_OpAMD64ADDQcarry_0(v)
 	case OpAMD64ADDQconst:
 		return rewriteValueAMD64_OpAMD64ADDQconst_0(v) || rewriteValueAMD64_OpAMD64ADDQconst_10(v)
 	case OpAMD64ADDQconstmodify:
@@ -1142,6 +1148,86 @@ func rewriteValueAMD64(v *Value) bool {
 	}
 	return false
 }
+func rewriteValueAMD64_OpAMD64ADCQ_0(v *Value) bool {
+	// match: (ADCQ x (MOVQconst [c]) carry)
+	// cond: is32Bit(c)
+	// result: (ADCQconst x [c] carry)
+	for {
+		_ = v.Args[2]
+		x := v.Args[0]
+		v_1 := v.Args[1]
+		if v_1.Op != OpAMD64MOVQconst {
+			break
+		}
+		c := v_1.AuxInt
+		carry := v.Args[2]
+		if !(is32Bit(c)) {
+			break
+		}
+		v.reset(OpAMD64ADCQconst)
+		v.AuxInt = c
+		v.AddArg(x)
+		v.AddArg(carry)
+		return true
+	}
+	// match: (ADCQ (MOVQconst [c]) x carry)
+	// cond: is32Bit(c)
+	// result: (ADCQconst x [c] carry)
+	for {
+		_ = v.Args[2]
+		v_0 := v.Args[0]
+		if v_0.Op != OpAMD64MOVQconst {
+			break
+		}
+		c := v_0.AuxInt
+		x := v.Args[1]
+		carry := v.Args[2]
+		if !(is32Bit(c)) {
+			break
+		}
+		v.reset(OpAMD64ADCQconst)
+		v.AuxInt = c
+		v.AddArg(x)
+		v.AddArg(carry)
+		return true
+	}
+	// match: (ADCQ x y (FlagEQ))
+	// cond:
+	// result: (ADDQcarry x y)
+	for {
+		_ = v.Args[2]
+		x := v.Args[0]
+		y := v.Args[1]
+		v_2 := v.Args[2]
+		if v_2.Op != OpAMD64FlagEQ {
+			break
+		}
+		v.reset(OpAMD64ADDQcarry)
+		v.AddArg(x)
+		v.AddArg(y)
+		return true
+	}
+	return false
+}
+func rewriteValueAMD64_OpAMD64ADCQconst_0(v *Value) bool {
+	// match: (ADCQconst x [c] (FlagEQ))
+	// cond:
+	// result: (ADDQconstcarry x [c])
+	for {
+		c := v.AuxInt
+		_ = v.Args[1]
+		x := v.Args[0]
+		v_1 := v.Args[1]
+		if v_1.Op != OpAMD64FlagEQ {
+			break
+		}
+		v.reset(OpAMD64ADDQconstcarry)
+		v.AuxInt = c
+		v.AddArg(x)
+		return true
+	}
+	return false
+}
 func rewriteValueAMD64_OpAMD64ADDL_0(v *Value) bool {
 	// match: (ADDL x (MOVLconst [c]))
 	// cond:
@@ -2667,6 +2753,47 @@ func rewriteValueAMD64_OpAMD64ADDQ_20(v *Value) bool {
 	}
 	return false
 }
+func rewriteValueAMD64_OpAMD64ADDQcarry_0(v *Value) bool {
+	// match: (ADDQcarry x (MOVQconst [c]))
+	// cond: is32Bit(c)
+	// result: (ADDQconstcarry x [c])
+	for {
+		_ = v.Args[1]
+		x := v.Args[0]
+		v_1 := v.Args[1]
+		if v_1.Op != OpAMD64MOVQconst {
+			break
+		}
+		c := v_1.AuxInt
+		if !(is32Bit(c)) {
+			break
+		}
+		v.reset(OpAMD64ADDQconstcarry)
+		v.AuxInt = c
+		v.AddArg(x)
+		return true
+	}
+	// match: (ADDQcarry (MOVQconst [c]) x)
+	// cond: is32Bit(c)
+	// result: (ADDQconstcarry x [c])
+	for {
+		_ = v.Args[1]
+		v_0 := v.Args[0]
+		if v_0.Op != OpAMD64MOVQconst {
+			break
+		}
+		c := v_0.AuxInt
+		x := v.Args[1]
+		if !(is32Bit(c)) {
+			break
+		}
+		v.reset(OpAMD64ADDQconstcarry)
+		v.AuxInt = c
+		v.AddArg(x)
+		return true
+	}
+	return false
+}
 func rewriteValueAMD64_OpAMD64ADDQconst_0(v *Value) bool {
 	// match: (ADDQconst [c] (ADDQ x y))
 	// cond:
@@ -64838,6 +64965,31 @@ func rewriteValueAMD64_OpSelect0_0(v *Value) bool {
 		v.AddArg(v0)
 		return true
 	}
+	// match: (Select0 (Add64carry x y c))
+	// cond:
+	// result: (Select0 <typ.UInt64> (ADCQ x y (Select1 <types.TypeFlags> (NEGLflags c))))
+	for {
+		v_0 := v.Args[0]
+		if v_0.Op != OpAdd64carry {
+			break
+		}
+		_ = v_0.Args[2]
+		x := v_0.Args[0]
+		y := v_0.Args[1]
+		c := v_0.Args[2]
+		v.reset(OpSelect0)
+		v.Type = typ.UInt64
+		v0 := b.NewValue0(v.Pos, OpAMD64ADCQ, types.NewTuple(typ.UInt64, types.TypeFlags))
+		v0.AddArg(x)
+		v0.AddArg(y)
+		v1 := b.NewValue0(v.Pos, OpSelect1, types.TypeFlags)
+		v2 := b.NewValue0(v.Pos, OpAMD64NEGLflags, types.NewTuple(typ.UInt32, types.TypeFlags))
+		v2.AddArg(c)
+		v1.AddArg(v2)
+		v0.AddArg(v1)
+		v.AddArg(v0)
+		return true
+	}
 	// match: (Select0 <t> (AddTupleFirst32 val tuple))
 	// cond:
 	// result: (ADDL val (Select0 <t> tuple))
@@ -64923,6 +65075,75 @@ func rewriteValueAMD64_OpSelect1_0(v *Value) bool {
 		v.AddArg(v0)
 		return true
 	}
+	// match: (Select1 (Add64carry x y c))
+	// cond:
+	// result: (NEGQ <typ.UInt64> (SBBQcarrymask <typ.UInt64> (Select1 <types.TypeFlags> (ADCQ x y (Select1 <types.TypeFlags> (NEGLflags c))))))
+	for {
+		v_0 := v.Args[0]
+		if v_0.Op != OpAdd64carry {
+			break
+		}
+		_ = v_0.Args[2]
+		x := v_0.Args[0]
+		y := v_0.Args[1]
+		c := v_0.Args[2]
+		v.reset(OpAMD64NEGQ)
+		v.Type = typ.UInt64
+		v0 := b.NewValue0(v.Pos, OpAMD64SBBQcarrymask, typ.UInt64)
+		v1 := b.NewValue0(v.Pos, OpSelect1, types.TypeFlags)
+		v2 := b.NewValue0(v.Pos, OpAMD64ADCQ, types.NewTuple(typ.UInt64, types.TypeFlags))
+		v2.AddArg(x)
+		v2.AddArg(y)
+		v3 := b.NewValue0(v.Pos, OpSelect1, types.TypeFlags)
+		v4 := b.NewValue0(v.Pos, OpAMD64NEGLflags, types.NewTuple(typ.UInt32, types.TypeFlags))
+		v4.AddArg(c)
+		v3.AddArg(v4)
+		v2.AddArg(v3)
+		v1.AddArg(v2)
+		v0.AddArg(v1)
+		v.AddArg(v0)
+		return true
+	}
+	// match: (Select1 (NEGLflags (MOVQconst [0])))
+	// cond:
+	// result: (FlagEQ)
+	for {
+		v_0 := v.Args[0]
+		if v_0.Op != OpAMD64NEGLflags {
+			break
+		}
+		v_0_0 := v_0.Args[0]
+		if v_0_0.Op != OpAMD64MOVQconst {
+			break
+		}
+		if v_0_0.AuxInt != 0 {
+			break
+		}
+		v.reset(OpAMD64FlagEQ)
+		return true
+	}
+	// match: (Select1 (NEGLflags (NEGQ (SBBQcarrymask x))))
+	// cond:
+	// result: x
+	for {
+		v_0 := v.Args[0]
+		if v_0.Op != OpAMD64NEGLflags {
+			break
+		}
+		v_0_0 := v_0.Args[0]
+		if v_0_0.Op != OpAMD64NEGQ {
+			break
+		}
+		v_0_0_0 := v_0_0.Args[0]
+		if v_0_0_0.Op != OpAMD64SBBQcarrymask {
+			break
+		}
+		x := v_0_0_0.Args[0]
+		v.reset(OpCopy)
+		v.Type = x.Type
+		v.AddArg(x)
+		return true
+	}
 	// match: (Select1 (AddTupleFirst32 _ tuple))
 	// cond:
 	// result: (Select1 tuple)

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

@@ -13,6 +13,7 @@ const (
 	ScoreReadTuple
 	ScoreVarDef
 	ScoreMemory
+	ScoreReadFlags
 	ScoreDefault
 	ScoreFlags
 	ScoreControl // towards bottom of block
@@ -129,13 +130,19 @@ func schedule(f *Func) {
 				// false dependency on the other part of the tuple.
 				// Also ensures tuple is never spilled.
 				score[v.ID] = ScoreReadTuple
-			case v.Type.IsFlags() || v.Type.IsTuple():
+			case v.Type.IsFlags() || v.Type.IsTuple() && v.Type.FieldType(1).IsFlags():
 				// Schedule flag register generation as late as possible.
 				// This makes sure that we only have one live flags
 				// value at a time.
 				score[v.ID] = ScoreFlags
 			default:
 				score[v.ID] = ScoreDefault
+				// If we're reading flags, schedule earlier to keep flag lifetime short.
+				for _, a := range v.Args {
+					if a.Type.IsFlags() {
+						score[v.ID] = ScoreReadFlags
+					}
+				}
 			}
 		}
 	}

src/math/bits/bits_test.go

@@ -899,6 +899,21 @@ func BenchmarkAdd64(b *testing.B) {
 	Output = int(z + c)
 }
 
+func BenchmarkAdd64multiple(b *testing.B) {
+	var z0 = uint64(Input)
+	var z1 = uint64(Input)
+	var z2 = uint64(Input)
+	var z3 = uint64(Input)
+	for i := 0; i < b.N; i++ {
+		var c uint64
+		z0, c = Add64(z0, uint64(i), c)
+		z1, c = Add64(z1, uint64(i), c)
+		z2, c = Add64(z2, uint64(i), c)
+		z3, _ = Add64(z3, uint64(i), c)
+	}
+	Output = int(z0 + z1 + z2 + z3)
+}
+
 func BenchmarkSub(b *testing.B) {
 	var z, c uint
 	for i := 0; i < b.N; i++ {
@@ -923,6 +938,21 @@ func BenchmarkSub64(b *testing.B) {
 	Output = int(z + c)
 }
 
+func BenchmarkSub64multiple(b *testing.B) {
+	var z0 = uint64(Input)
+	var z1 = uint64(Input)
+	var z2 = uint64(Input)
+	var z3 = uint64(Input)
+	for i := 0; i < b.N; i++ {
+		var c uint64
+		z0, c = Sub64(z0, uint64(i), c)
+		z1, c = Sub64(z1, uint64(i), c)
+		z2, c = Sub64(z2, uint64(i), c)
+		z3, _ = Sub64(z3, uint64(i), c)
+	}
+	Output = int(z0 + z1 + z2 + z3)
+}
+
 func BenchmarkMul(b *testing.B) {
 	var hi, lo uint
 	for i := 0; i < b.N; i++ {

test/codegen/mathbits.go

@@ -326,6 +326,66 @@ func IterateBits8(n uint8) int {
 	return i
 }
 
+// --------------- //
+//    bits.Add*    //
+// --------------- //
+
+func Add(x, y, ci uint) (r, co uint) {
+	// amd64:"NEGL","ADCQ","SBBQ","NEGQ"
+	return bits.Add(x, y, ci)
+}
+
+func AddC(x, ci uint) (r, co uint) {
+	// amd64:"NEGL","ADCQ","SBBQ","NEGQ"
+	return bits.Add(x, 7, ci)
+}
+
+func AddZ(x, y uint) (r, co uint) {
+	// amd64:"ADDQ","SBBQ","NEGQ",-"NEGL",-"ADCQ"
+	return bits.Add(x, y, 0)
+}
+
+func AddR(x, y, ci uint) uint {
+	// amd64:"NEGL","ADCQ",-"SBBQ",-"NEGQ"
+	r, _ := bits.Add(x, y, ci)
+	return r
+}
+func AddM(p, q, r *[3]uint) {
+	var c uint
+	r[0], c = bits.Add(p[0], q[0], c)
+	// amd64:"ADCQ",-"NEGL",-"SBBQ",-"NEGQ"
+	r[1], c = bits.Add(p[1], q[1], c)
+	r[2], c = bits.Add(p[2], q[2], c)
+}
+
+func Add64(x, y, ci uint64) (r, co uint64) {
+	// amd64:"NEGL","ADCQ","SBBQ","NEGQ"
+	return bits.Add64(x, y, ci)
+}
+
+func Add64C(x, ci uint64) (r, co uint64) {
+	// amd64:"NEGL","ADCQ","SBBQ","NEGQ"
+	return bits.Add64(x, 7, ci)
+}
+
+func Add64Z(x, y uint64) (r, co uint64) {
+	// amd64:"ADDQ","SBBQ","NEGQ",-"NEGL",-"ADCQ"
+	return bits.Add64(x, y, 0)
+}
+
+func Add64R(x, y, ci uint64) uint64 {
+	// amd64:"NEGL","ADCQ",-"SBBQ",-"NEGQ"
+	r, _ := bits.Add64(x, y, ci)
+	return r
+}
+func Add64M(p, q, r *[3]uint64) {
+	var c uint64
+	r[0], c = bits.Add64(p[0], q[0], c)
+	// amd64:"ADCQ",-"NEGL",-"SBBQ",-"NEGQ"
+	r[1], c = bits.Add64(p[1], q[1], c)
+	r[2], c = bits.Add64(p[2], q[2], c)
+}
+
 // --------------- //
 //    bits.Mul*    //
 // --------------- //