cmd/compile: better job of naming compound types

Compound AUTO types weren't named previously.  That was because live
variable analysis (plive.go) doesn't handle spilling to compound types.
It can't handle them because there is no valid place to put VARDEFs when
regalloc is spilling compound types.

compound types = multiword builtin types: complex, string, slice, and
interface.

Instead, we split named AUTOs into individual one-word variables.  For
example, a string s gets split into a byte ptr s.ptr and an integer
s.len.  Those two variables can be spilled to / restored from
independently.  As a result, live variable analysis can handle them
because they are one-word objects.

This CL will change how AUTOs are described in DWARF information.
Consider the code:

func f(s string, i int) int {
    x := s[i:i+5]
    g()
    return lookup(x)
}

The old compiler would spill x to two consecutive slots on the stack,
both named x (at offsets 0 and 8).  The new compiler spills the pointer
of x to a slot named x.ptr.  It doesn't spill x.len at all, as it is a
constant (5) and can be rematerialized for the call to lookup.

So compound objects may not be spilled in their entirety, and even if
they are they won't necessarily be contiguous.  Such is the price of
optimization.

Re-enable live variable analysis tests.  One test remains disabled, it
fails because of #14904.

Change-Id: I8ef2b5ab91e43a0d2136bfc231c05d100ec0b801
Reviewed-on: https://go-review.googlesource.com/21233
Run-TryBot: Keith Randall <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: David Chase <[email protected]>

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

@@ -3762,12 +3762,6 @@ func (s *state) addNamedValue(n *Node, v *ssa.Value) {
 		// Don't track autotmp_ variables.
 		return
 	}
-	if n.Class == PAUTO && (v.Type.IsString() || v.Type.IsSlice() || v.Type.IsInterface()) {
-		// TODO: can't handle auto compound objects with pointers yet.
-		// The live variable analysis barfs because we don't put VARDEF
-		// pseudos in the right place when we spill to these nodes.
-		return
-	}
 	if n.Class == PPARAMOUT {
 		// Don't track named output values.  This prevents return values
 		// from being assigned too early. See #14591 and #14762. TODO: allow this.
@@ -4175,6 +4169,96 @@ func (e *ssaExport) Auto(t ssa.Type) ssa.GCNode {
 	return n
 }
 
+func (e *ssaExport) SplitString(name ssa.LocalSlot) (ssa.LocalSlot, ssa.LocalSlot) {
+	n := name.N.(*Node)
+	ptrType := Ptrto(Types[TUINT8])
+	lenType := Types[TINT]
+	if n.Class == PAUTO && !n.Addrtaken {
+		// Split this string up into two separate variables.
+		p := e.namedAuto(n.Sym.Name+".ptr", ptrType)
+		l := e.namedAuto(n.Sym.Name+".len", lenType)
+		return ssa.LocalSlot{p, ptrType, 0}, ssa.LocalSlot{l, lenType, 0}
+	}
+	// Return the two parts of the larger variable.
+	return ssa.LocalSlot{n, ptrType, name.Off}, ssa.LocalSlot{n, lenType, name.Off + int64(Widthptr)}
+}
+
+func (e *ssaExport) SplitInterface(name ssa.LocalSlot) (ssa.LocalSlot, ssa.LocalSlot) {
+	n := name.N.(*Node)
+	t := Ptrto(Types[TUINT8])
+	if n.Class == PAUTO && !n.Addrtaken {
+		// Split this interface up into two separate variables.
+		f := ".itab"
+		if isnilinter(n.Type) {
+			f = ".type"
+		}
+		c := e.namedAuto(n.Sym.Name+f, t)
+		d := e.namedAuto(n.Sym.Name+".data", t)
+		return ssa.LocalSlot{c, t, 0}, ssa.LocalSlot{d, t, 0}
+	}
+	// Return the two parts of the larger variable.
+	return ssa.LocalSlot{n, t, name.Off}, ssa.LocalSlot{n, t, name.Off + int64(Widthptr)}
+}
+
+func (e *ssaExport) SplitSlice(name ssa.LocalSlot) (ssa.LocalSlot, ssa.LocalSlot, ssa.LocalSlot) {
+	n := name.N.(*Node)
+	ptrType := Ptrto(n.Type.Type)
+	lenType := Types[TINT]
+	if n.Class == PAUTO && !n.Addrtaken {
+		// Split this slice up into three separate variables.
+		p := e.namedAuto(n.Sym.Name+".ptr", ptrType)
+		l := e.namedAuto(n.Sym.Name+".len", lenType)
+		c := e.namedAuto(n.Sym.Name+".cap", lenType)
+		return ssa.LocalSlot{p, ptrType, 0}, ssa.LocalSlot{l, lenType, 0}, ssa.LocalSlot{c, lenType, 0}
+	}
+	// Return the three parts of the larger variable.
+	return ssa.LocalSlot{n, ptrType, name.Off},
+		ssa.LocalSlot{n, lenType, name.Off + int64(Widthptr)},
+		ssa.LocalSlot{n, lenType, name.Off + int64(2*Widthptr)}
+}
+
+func (e *ssaExport) SplitComplex(name ssa.LocalSlot) (ssa.LocalSlot, ssa.LocalSlot) {
+	n := name.N.(*Node)
+	s := name.Type.Size() / 2
+	var t *Type
+	if s == 8 {
+		t = Types[TFLOAT64]
+	} else {
+		t = Types[TFLOAT32]
+	}
+	if n.Class == PAUTO && !n.Addrtaken {
+		// Split this complex up into two separate variables.
+		c := e.namedAuto(n.Sym.Name+".real", t)
+		d := e.namedAuto(n.Sym.Name+".imag", t)
+		return ssa.LocalSlot{c, t, 0}, ssa.LocalSlot{d, t, 0}
+	}
+	// Return the two parts of the larger variable.
+	return ssa.LocalSlot{n, t, name.Off}, ssa.LocalSlot{n, t, name.Off + s}
+}
+
+// namedAuto returns a new AUTO variable with the given name and type.
+func (e *ssaExport) namedAuto(name string, typ ssa.Type) ssa.GCNode {
+	t := typ.(*Type)
+	s := Lookup(name)
+	n := Nod(ONAME, nil, nil)
+	s.Def = n
+	s.Def.Used = true
+	n.Sym = s
+	n.Type = t
+	n.Class = PAUTO
+	n.Addable = true
+	n.Ullman = 1
+	n.Esc = EscNever
+	n.Xoffset = 0
+	n.Name.Curfn = Curfn
+	Curfn.Func.Dcl = append(Curfn.Func.Dcl, n)
+
+	dowidth(t)
+	e.mustImplement = true
+
+	return n
+}
+
 func (e *ssaExport) CanSSA(t ssa.Type) bool {
 	return canSSAType(t.(*Type))
 }

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

@@ -97,6 +97,13 @@ type Frontend interface {
 	// The SSA compiler uses this function to allocate space for spills.
 	Auto(Type) GCNode
 
+	// Given the name for a compound type, returns the name we should use
+	// for the parts of that compound type.
+	SplitString(LocalSlot) (LocalSlot, LocalSlot)
+	SplitInterface(LocalSlot) (LocalSlot, LocalSlot)
+	SplitSlice(LocalSlot) (LocalSlot, LocalSlot, LocalSlot)
+	SplitComplex(LocalSlot) (LocalSlot, LocalSlot)
+
 	// Line returns a string describing the given line number.
 	Line(int32) string
 }

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

@@ -31,8 +31,7 @@ func decomposeBuiltIn(f *Func) {
 			} else {
 				elemType = f.Config.fe.TypeFloat32()
 			}
-			rName := LocalSlot{name.N, elemType, name.Off}
-			iName := LocalSlot{name.N, elemType, name.Off + elemType.Size()}
+			rName, iName := f.Config.fe.SplitComplex(name)
 			f.Names = append(f.Names, rName, iName)
 			for _, v := range f.NamedValues[name] {
 				r := v.Block.NewValue1(v.Line, OpComplexReal, elemType, v)
@@ -43,8 +42,7 @@ func decomposeBuiltIn(f *Func) {
 		case t.IsString():
 			ptrType := f.Config.fe.TypeBytePtr()
 			lenType := f.Config.fe.TypeInt()
-			ptrName := LocalSlot{name.N, ptrType, name.Off}
-			lenName := LocalSlot{name.N, lenType, name.Off + f.Config.PtrSize}
+			ptrName, lenName := f.Config.fe.SplitString(name)
 			f.Names = append(f.Names, ptrName, lenName)
 			for _, v := range f.NamedValues[name] {
 				ptr := v.Block.NewValue1(v.Line, OpStringPtr, ptrType, v)
@@ -55,9 +53,7 @@ func decomposeBuiltIn(f *Func) {
 		case t.IsSlice():
 			ptrType := f.Config.fe.TypeBytePtr()
 			lenType := f.Config.fe.TypeInt()
-			ptrName := LocalSlot{name.N, ptrType, name.Off}
-			lenName := LocalSlot{name.N, lenType, name.Off + f.Config.PtrSize}
-			capName := LocalSlot{name.N, lenType, name.Off + 2*f.Config.PtrSize}
+			ptrName, lenName, capName := f.Config.fe.SplitSlice(name)
 			f.Names = append(f.Names, ptrName, lenName, capName)
 			for _, v := range f.NamedValues[name] {
 				ptr := v.Block.NewValue1(v.Line, OpSlicePtr, ptrType, v)
@@ -69,8 +65,7 @@ func decomposeBuiltIn(f *Func) {
 			}
 		case t.IsInterface():
 			ptrType := f.Config.fe.TypeBytePtr()
-			typeName := LocalSlot{name.N, ptrType, name.Off}
-			dataName := LocalSlot{name.N, ptrType, name.Off + f.Config.PtrSize}
+			typeName, dataName := f.Config.fe.SplitInterface(name)
 			f.Names = append(f.Names, typeName, dataName)
 			for _, v := range f.NamedValues[name] {
 				typ := v.Block.NewValue1(v.Line, OpITab, ptrType, v)

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

@@ -31,6 +31,23 @@ func (DummyFrontend) StringData(s string) interface{} {
 func (DummyFrontend) Auto(t Type) GCNode {
 	return nil
 }
+func (d DummyFrontend) SplitString(s LocalSlot) (LocalSlot, LocalSlot) {
+	return LocalSlot{s.N, d.TypeBytePtr(), s.Off}, LocalSlot{s.N, d.TypeInt(), s.Off + 8}
+}
+func (d DummyFrontend) SplitInterface(s LocalSlot) (LocalSlot, LocalSlot) {
+	return LocalSlot{s.N, d.TypeBytePtr(), s.Off}, LocalSlot{s.N, d.TypeBytePtr(), s.Off + 8}
+}
+func (d DummyFrontend) SplitSlice(s LocalSlot) (LocalSlot, LocalSlot, LocalSlot) {
+	return LocalSlot{s.N, s.Type.ElemType().PtrTo(), s.Off},
+		LocalSlot{s.N, d.TypeInt(), s.Off + 8},
+		LocalSlot{s.N, d.TypeInt(), s.Off + 16}
+}
+func (d DummyFrontend) SplitComplex(s LocalSlot) (LocalSlot, LocalSlot) {
+	if s.Type.Size() == 16 {
+		return LocalSlot{s.N, d.TypeFloat64(), s.Off}, LocalSlot{s.N, d.TypeFloat64(), s.Off + 8}
+	}
+	return LocalSlot{s.N, d.TypeFloat32(), s.Off}, LocalSlot{s.N, d.TypeFloat32(), s.Off + 4}
+}
 func (DummyFrontend) Line(line int32) string {
 	return "unknown.go:0"
 }

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

@@ -1,6 +1,92 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file contains rules to decompose builtin compound types
+// (complex,string,slice,interface) into their constituent
+// types.  These rules work together with the decomposeBuiltIn
+// pass which handles phis of these types.
+
+// complex ops
+(ComplexReal (ComplexMake real _  )) -> real
+(ComplexImag (ComplexMake _ imag )) -> imag
+
+(Load <t> ptr mem) && t.IsComplex() && t.Size() == 8 ->
+  (ComplexMake
+    (Load <config.fe.TypeFloat32()> ptr mem)
+    (Load <config.fe.TypeFloat32()>
+      (OffPtr <config.fe.TypeFloat32().PtrTo()> [4] ptr)
+      mem)
+    )
+(Store [8] dst (ComplexMake real imag) mem) ->
+  (Store [4]
+    (OffPtr <config.fe.TypeFloat32().PtrTo()> [4] dst)
+    imag
+    (Store [4] dst real mem))
+(Load <t> ptr mem) && t.IsComplex() && t.Size() == 16 ->
+  (ComplexMake
+    (Load <config.fe.TypeFloat64()> ptr mem)
+    (Load <config.fe.TypeFloat64()>
+      (OffPtr <config.fe.TypeFloat64().PtrTo()> [8] ptr)
+      mem)
+    )
+(Store [16] dst (ComplexMake real imag) mem) ->
+  (Store [8]
+    (OffPtr <config.fe.TypeFloat64().PtrTo()> [8] dst)
+    imag
+    (Store [8] dst real mem))
+
+// string ops
 (StringPtr (StringMake ptr _)) -> ptr
 (StringLen (StringMake _ len)) -> len
 
+(Load <t> ptr mem) && t.IsString() ->
+  (StringMake
+    (Load <config.fe.TypeBytePtr()> ptr mem)
+    (Load <config.fe.TypeInt()>
+      (OffPtr <config.fe.TypeInt().PtrTo()> [config.PtrSize] ptr)
+      mem))
+(Store [2*config.PtrSize] dst (StringMake ptr len) mem) ->
+  (Store [config.PtrSize]
+    (OffPtr <config.fe.TypeInt().PtrTo()> [config.PtrSize] dst)
+    len
+    (Store [config.PtrSize] dst ptr mem))
+
+// slice ops
 (SlicePtr (SliceMake ptr _ _ )) -> ptr
 (SliceLen (SliceMake _ len _)) -> len
 (SliceCap (SliceMake _ _ cap)) -> cap
+
+(Load <t> ptr mem) && t.IsSlice() ->
+  (SliceMake
+    (Load <t.ElemType().PtrTo()> ptr mem)
+    (Load <config.fe.TypeInt()>
+      (OffPtr <config.fe.TypeInt().PtrTo()> [config.PtrSize] ptr)
+      mem)
+    (Load <config.fe.TypeInt()>
+      (OffPtr <config.fe.TypeInt().PtrTo()> [2*config.PtrSize] ptr)
+      mem))
+(Store [3*config.PtrSize] dst (SliceMake ptr len cap) mem) ->
+  (Store [config.PtrSize]
+    (OffPtr <config.fe.TypeInt().PtrTo()> [2*config.PtrSize] dst)
+    cap
+    (Store [config.PtrSize]
+      (OffPtr <config.fe.TypeInt().PtrTo()> [config.PtrSize] dst)
+      len
+      (Store [config.PtrSize] dst ptr mem)))
+
+// interface ops
+(ITab (IMake itab _)) -> itab
+(IData (IMake _ data)) -> data
+
+(Load <t> ptr mem) && t.IsInterface() ->
+  (IMake
+    (Load <config.fe.TypeBytePtr()> ptr mem)
+    (Load <config.fe.TypeBytePtr()>
+      (OffPtr <config.fe.TypeBytePtr().PtrTo()> [config.PtrSize] ptr)
+      mem))
+(Store [2*config.PtrSize] dst (IMake itab data) mem) ->
+  (Store [config.PtrSize]
+    (OffPtr <config.fe.TypeBytePtr().PtrTo()> [config.PtrSize] dst)
+    data
+    (Store [config.PtrSize] dst itab mem))