[dev.ssa] cmd/compile/internal/ssa: Initial implementation of memory zeroing

This will make it possible for us to start implementing interfaces
and other stack allocated types which are more than one machine word.

Change-Id: I52b187a791cf1919cb70ed6dabdc9f57b317ea83
Reviewed-on: https://go-review.googlesource.com/11631Reviewed-by: Keith Randall <khr@golang.org>

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

@@ -223,6 +223,11 @@ func (s *state) newValue2(op ssa.Op, t ssa.Type, arg0, arg1 *ssa.Value) *ssa.Val
 	return s.curBlock.NewValue2(s.peekLine(), op, t, arg0, arg1)
 }
 
+// newValue2I adds a new value with two arguments and an auxint value to the current block.
+func (s *state) newValue2I(op ssa.Op, t ssa.Type, aux int64, arg0, arg1 *ssa.Value) *ssa.Value {
+	return s.curBlock.NewValue2I(s.peekLine(), op, t, aux, arg0, arg1)
+}
+
 // newValue3 adds a new value with three arguments to the current block.
 func (s *state) newValue3(op ssa.Op, t ssa.Type, arg0, arg1, arg2 *ssa.Value) *ssa.Value {
 	return s.curBlock.NewValue3(s.peekLine(), op, t, arg0, arg1, arg2)
@@ -554,6 +559,12 @@ func (s *state) assign(op uint8, left *Node, right *Node) {
 	if right == nil {
 		// right == nil means use the zero value of the assigned type.
 		t := left.Type
+		if !canSSA(left) {
+			// if we can't ssa this memory, treat it as just zeroing out the backing memory
+			addr := s.addr(left)
+			s.vars[&memvar] = s.newValue2I(ssa.OpZero, ssa.TypeMem, t.Size(), addr, s.mem())
+			return
+		}
 		switch {
 		case t.IsString():
 			val = s.entryNewValue0A(ssa.OpConst, left.Type, "")
@@ -624,7 +635,7 @@ func (s *state) addr(n *Node) *ssa.Value {
 // n must be an ONAME.
 func canSSA(n *Node) bool {
 	if n.Op != ONAME {
-		Fatal("canSSA passed a non-ONAME %s %v", Oconv(int(n.Op), 0), n)
+		return false
 	}
 	if n.Addrtaken {
 		return false
@@ -638,6 +649,9 @@ func canSSA(n *Node) bool {
 	if n.Class == PPARAMOUT {
 		return false
 	}
+	if Isfat(n.Type) {
+		return false
+	}
 	return true
 	// TODO: try to make more variables SSAable.
 }
@@ -1062,6 +1076,22 @@ func genValue(v *ssa.Value) {
 		p.From.Reg = regnum(v.Args[0])
 		p.To.Type = obj.TYPE_REG
 		p.To.Reg = regnum(v)
+	case ssa.OpAMD64MOVXzero:
+		nb := v.AuxInt
+		offset := int64(0)
+		reg := regnum(v.Args[0])
+		for nb >= 8 {
+			nb, offset = movZero(x86.AMOVQ, 8, nb, offset, reg)
+		}
+		for nb >= 4 {
+			nb, offset = movZero(x86.AMOVL, 4, nb, offset, reg)
+		}
+		for nb >= 2 {
+			nb, offset = movZero(x86.AMOVW, 2, nb, offset, reg)
+		}
+		for nb >= 1 {
+			nb, offset = movZero(x86.AMOVB, 1, nb, offset, reg)
+		}
 	case ssa.OpCopy: // TODO: lower to MOVQ earlier?
 		if v.Type.IsMemory() {
 			return
@@ -1121,6 +1151,20 @@ func genValue(v *ssa.Value) {
 	}
 }
 
+// movZero generates a register indirect move with a 0 immediate and keeps track of bytes left and next offset
+func movZero(as int, width int64, nbytes int64, offset int64, regnum int16) (nleft int64, noff int64) {
+	p := Prog(as)
+	// TODO: use zero register on archs that support it.
+	p.From.Type = obj.TYPE_CONST
+	p.From.Offset = 0
+	p.To.Type = obj.TYPE_MEM
+	p.To.Reg = regnum
+	p.To.Offset = offset
+	offset += width
+	nleft = nbytes - width
+	return nleft, offset
+}
+
 func genBlock(b, next *ssa.Block, branches []branch) []branch {
 	lineno = b.Line
 	switch b.Kind {

src/cmd/compile/internal/ssa/TODO

@@ -59,3 +59,5 @@ Other
    checkOpcodeCounts.  Michael Matloob suggests using a similar
    pattern matcher to the rewrite engine to check for certain
    expression subtrees in the output.
+ - Implement memory zeroing with REPSTOSQ and DuffZero
+ - make deadstore work with zeroing.

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

@@ -188,6 +188,23 @@ func (b *Block) NewValue2(line int32, op Op, t Type, arg0, arg1 *Value) *Value {
 	return v
 }
 
+// NewValue2I returns a new value in the block with two arguments and an auxint value.
+func (b *Block) NewValue2I(line int32, op Op, t Type, aux int64, arg0, arg1 *Value) *Value {
+	v := &Value{
+		ID:     b.Func.vid.get(),
+		Op:     op,
+		Type:   t,
+		AuxInt: aux,
+		Block:  b,
+		Line:   line,
+	}
+	v.Args = v.argstorage[:2]
+	v.Args[0] = arg0
+	v.Args[1] = arg1
+	b.Values = append(b.Values, v)
+	return v
+}
+
 // NewValue3 returns a new value in the block with three arguments and zero aux values.
 func (b *Block) NewValue3(line int32, op Op, t Type, arg0, arg1, arg2 *Value) *Value {
 	v := &Value{

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

@@ -137,6 +137,18 @@
 
 (ADDQconst [0] x) -> (Copy x)
 
+// lower Zero instructions with word sizes
+(Zero [0] _ mem) -> (Copy mem)
+(Zero [1] destptr mem) -> (MOVBstore destptr (Const <TypeInt8> [0]) mem)
+(Zero [2] destptr mem) -> (MOVWstore destptr (Const <TypeInt16> [0]) mem)
+(Zero [4] destptr mem) -> (MOVLstore destptr (Const <TypeInt32> [0]) mem)
+(Zero [8] destptr mem) -> (MOVQstore destptr (Const <TypeInt64> [0]) mem)
+
+// rewrite anything less than 4 words into a series of MOV[BWLQ] $0, ptr(off) instructions
+(Zero [size] destptr mem) && size < 4*8 -> (MOVXzero [size] destptr mem)
+// Use STOSQ to zero memory. Rewrite this into storing the words with REPSTOSQ and then filling in the remainder with linear moves
+(Zero [size] destptr mem) && size >= 4*8 -> (Zero [size%8] (OffPtr <TypeUInt64> [size-(size%8)] destptr) (REPSTOSQ  <TypeMem> destptr (Const <TypeUInt64> [size/8]) mem))
+
 // Absorb InvertFlags into branches.
 (LT (InvertFlags cmp) yes no) -> (GT cmp yes no)
 (GT (InvertFlags cmp) yes no) -> (LT cmp yes no)

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

@@ -86,6 +86,7 @@ func init() {
 	gpload := regInfo{[]regMask{gpspsb, 0}, 0, []regMask{gp}}
 	gploadidx := regInfo{[]regMask{gpspsb, gpsp, 0}, 0, []regMask{gp}}
 	gpstore := regInfo{[]regMask{gpspsb, gpsp, 0}, 0, nil}
+	gpstoreconst := regInfo{[]regMask{gpspsb, 0}, 0, nil}
 	gpstoreidx := regInfo{[]regMask{gpspsb, gpsp, gpsp, 0}, 0, nil}
 	flagsgp := regInfo{[]regMask{flags}, 0, []regMask{gp}}
 	cmov := regInfo{[]regMask{flags, gp, gp}, 0, []regMask{gp}}
@@ -153,6 +154,10 @@ func init() {
 		{name: "MOVQstore", reg: gpstore, asm: "MOVQ"},      // store 8 bytes in arg1 to arg0+auxint. arg2=mem
 		{name: "MOVQstoreidx8", reg: gpstoreidx},            // store 8 bytes in arg2 to arg0+8*arg1+auxint. arg3=mem
 
+		{name: "MOVXzero", reg: gpstoreconst}, // store auxint 0 bytes into arg0 using a series of MOV instructions. arg1=mem.
+		// TODO: implement this when register clobbering works
+		{name: "REPSTOSQ", reg: regInfo{[]regMask{buildReg("DI"), buildReg("CX")}, buildReg("DI AX CX"), nil}}, // store arg1 8-byte words containing zero into arg0 using STOSQ. arg2=mem.
+
 		// Load/store from global. Same as the above loads, but arg0 is missing and
 		// aux is a GlobalOffset instead of an int64.
 		{name: "MOVQloadglobal"},  // Load from aux.(GlobalOffset).  arg0 = memory

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

@@ -51,6 +51,7 @@ var genericOps = []opData{
 	{name: "Load"},  // Load from arg0.  arg1=memory
 	{name: "Store"}, // Store arg1 to arg0.  arg2=memory.  Returns memory.
 	{name: "Move"},  // arg0=destptr, arg1=srcptr, arg2=mem, auxint=size.  Returns memory.
+	{name: "Zero"},  // arg0=destptr, arg1=mem, auxint=size. Returns memory.
 
 	// Function calls.  Arguments to the call have already been written to the stack.
 	// Return values appear on the stack.  The method receiver, if any, is treated

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

@@ -98,6 +98,8 @@ const (
 	OpAMD64MOVLstore
 	OpAMD64MOVQstore
 	OpAMD64MOVQstoreidx8
+	OpAMD64MOVXzero
+	OpAMD64REPSTOSQ
 	OpAMD64MOVQloadglobal
 	OpAMD64MOVQstoreglobal
 	OpAMD64CALLstatic
@@ -130,6 +132,7 @@ const (
 	OpLoad
 	OpStore
 	OpMove
+	OpZero
 	OpClosureCall
 	OpStaticCall
 	OpConvert
@@ -794,6 +797,28 @@ var opcodeTable = [...]opInfo{
 			outputs:  []regMask{},
 		},
 	},
+	{
+		name: "MOVXzero",
+		reg: regInfo{
+			inputs: []regMask{
+				4295032831, // .AX .CX .DX .BX .SP .BP .SI .DI .R8 .R9 .R10 .R11 .R12 .R13 .R14 .R15 .SB
+				0,
+			},
+			clobbers: 0,
+			outputs:  []regMask{},
+		},
+	},
+	{
+		name: "REPSTOSQ",
+		reg: regInfo{
+			inputs: []regMask{
+				128, // .DI
+				2,   // .CX
+			},
+			clobbers: 131, // .AX .CX .DI
+			outputs:  []regMask{},
+		},
+	},
 	{
 		name: "MOVQloadglobal",
 		reg: regInfo{
@@ -1091,6 +1116,15 @@ var opcodeTable = [...]opInfo{
 		},
 		generic: true,
 	},
+	{
+		name: "Zero",
+		reg: regInfo{
+			inputs:   []regMask{},
+			clobbers: 0,
+			outputs:  []regMask{},
+		},
+		generic: true,
+	},
 	{
 		name: "ClosureCall",
 		reg: regInfo{

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

@@ -1647,6 +1647,177 @@ func rewriteValueAMD64(v *Value, config *Config) bool {
 		}
 		goto ende6ef29f885a8ecf3058212bb95917323
 	ende6ef29f885a8ecf3058212bb95917323:
+		;
+	case OpZero:
+		// match: (Zero [0] _ mem)
+		// cond:
+		// result: (Copy mem)
+		{
+			if v.AuxInt != 0 {
+				goto endb85a34a7d102b0e0d801454f437db5bf
+			}
+			mem := v.Args[1]
+			v.Op = OpCopy
+			v.AuxInt = 0
+			v.Aux = nil
+			v.resetArgs()
+			v.AddArg(mem)
+			return true
+		}
+		goto endb85a34a7d102b0e0d801454f437db5bf
+	endb85a34a7d102b0e0d801454f437db5bf:
+		;
+		// match: (Zero [1] destptr mem)
+		// cond:
+		// result: (MOVBstore destptr (Const <TypeInt8> [0]) mem)
+		{
+			if v.AuxInt != 1 {
+				goto end09ec7b1fc5ad40534e0e25c896323f5c
+			}
+			destptr := v.Args[0]
+			mem := v.Args[1]
+			v.Op = OpAMD64MOVBstore
+			v.AuxInt = 0
+			v.Aux = nil
+			v.resetArgs()
+			v.AddArg(destptr)
+			v0 := v.Block.NewValue0(v.Line, OpConst, TypeInvalid)
+			v0.Type = TypeInt8
+			v0.AuxInt = 0
+			v.AddArg(v0)
+			v.AddArg(mem)
+			return true
+		}
+		goto end09ec7b1fc5ad40534e0e25c896323f5c
+	end09ec7b1fc5ad40534e0e25c896323f5c:
+		;
+		// match: (Zero [2] destptr mem)
+		// cond:
+		// result: (MOVWstore destptr (Const <TypeInt16> [0]) mem)
+		{
+			if v.AuxInt != 2 {
+				goto end2dee246789dbd305bb1eaec768bdae14
+			}
+			destptr := v.Args[0]
+			mem := v.Args[1]
+			v.Op = OpAMD64MOVWstore
+			v.AuxInt = 0
+			v.Aux = nil
+			v.resetArgs()
+			v.AddArg(destptr)
+			v0 := v.Block.NewValue0(v.Line, OpConst, TypeInvalid)
+			v0.Type = TypeInt16
+			v0.AuxInt = 0
+			v.AddArg(v0)
+			v.AddArg(mem)
+			return true
+		}
+		goto end2dee246789dbd305bb1eaec768bdae14
+	end2dee246789dbd305bb1eaec768bdae14:
+		;
+		// match: (Zero [4] destptr mem)
+		// cond:
+		// result: (MOVLstore destptr (Const <TypeInt32> [0]) mem)
+		{
+			if v.AuxInt != 4 {
+				goto ende2bf4ecf21bc9e76700a9c5f62546e78
+			}
+			destptr := v.Args[0]
+			mem := v.Args[1]
+			v.Op = OpAMD64MOVLstore
+			v.AuxInt = 0
+			v.Aux = nil
+			v.resetArgs()
+			v.AddArg(destptr)
+			v0 := v.Block.NewValue0(v.Line, OpConst, TypeInvalid)
+			v0.Type = TypeInt32
+			v0.AuxInt = 0
+			v.AddArg(v0)
+			v.AddArg(mem)
+			return true
+		}
+		goto ende2bf4ecf21bc9e76700a9c5f62546e78
+	ende2bf4ecf21bc9e76700a9c5f62546e78:
+		;
+		// match: (Zero [8] destptr mem)
+		// cond:
+		// result: (MOVQstore destptr (Const <TypeInt64> [0]) mem)
+		{
+			if v.AuxInt != 8 {
+				goto enda65d5d60783daf9b9405f04c44f7adaf
+			}
+			destptr := v.Args[0]
+			mem := v.Args[1]
+			v.Op = OpAMD64MOVQstore
+			v.AuxInt = 0
+			v.Aux = nil
+			v.resetArgs()
+			v.AddArg(destptr)
+			v0 := v.Block.NewValue0(v.Line, OpConst, TypeInvalid)
+			v0.Type = TypeInt64
+			v0.AuxInt = 0
+			v.AddArg(v0)
+			v.AddArg(mem)
+			return true
+		}
+		goto enda65d5d60783daf9b9405f04c44f7adaf
+	enda65d5d60783daf9b9405f04c44f7adaf:
+		;
+		// match: (Zero [size] destptr mem)
+		// cond: size < 4*8
+		// result: (MOVXzero [size] destptr mem)
+		{
+			size := v.AuxInt
+			destptr := v.Args[0]
+			mem := v.Args[1]
+			if !(size < 4*8) {
+				goto endf0a22f1506977610ac0a310eee152075
+			}
+			v.Op = OpAMD64MOVXzero
+			v.AuxInt = 0
+			v.Aux = nil
+			v.resetArgs()
+			v.AuxInt = size
+			v.AddArg(destptr)
+			v.AddArg(mem)
+			return true
+		}
+		goto endf0a22f1506977610ac0a310eee152075
+	endf0a22f1506977610ac0a310eee152075:
+		;
+		// match: (Zero [size] destptr mem)
+		// cond: size >= 4*8
+		// result: (Zero [size%8] (OffPtr <TypeUInt64> [size-(size%8)] destptr) (REPSTOSQ  <TypeMem> destptr (Const <TypeUInt64> [size/8]) mem))
+		{
+			size := v.AuxInt
+			destptr := v.Args[0]
+			mem := v.Args[1]
+			if !(size >= 4*8) {
+				goto end7a358169d20d6834b21f2e03fbf351b2
+			}
+			v.Op = OpZero
+			v.AuxInt = 0
+			v.Aux = nil
+			v.resetArgs()
+			v.AuxInt = size % 8
+			v0 := v.Block.NewValue0(v.Line, OpOffPtr, TypeInvalid)
+			v0.Type = TypeUInt64
+			v0.AuxInt = size - (size % 8)
+			v0.AddArg(destptr)
+			v.AddArg(v0)
+			v1 := v.Block.NewValue0(v.Line, OpAMD64REPSTOSQ, TypeInvalid)
+			v1.Type = TypeMem
+			v1.AddArg(destptr)
+			v2 := v.Block.NewValue0(v.Line, OpConst, TypeInvalid)
+			v2.Type = TypeUInt64
+			v2.AuxInt = size / 8
+			v1.AddArg(v2)
+			v1.AddArg(mem)
+			v.AddArg(v1)
+			return true
+		}
+		goto end7a358169d20d6834b21f2e03fbf351b2
+	end7a358169d20d6834b21f2e03fbf351b2:
 	}
 	return false
 }