prog: refactor bitfields representation

All callers of BitfieldMiddle just want static size (0 for middle).
Make it so: Size for middle bitfields just returns 0. Removes lots of if's.
Introduce Type.UnitSize, which now holds the underlying type for bitfields.
This will be needed to fix #1542 b/c even if UnitSize=4 for last bitfield
Size can be anywhere from 0 to 4 (not necessary equal to UnitSize due to overlapping).

6 files changed, 42 insertions, 32 deletions

diff --git a/prog/analysis.go b/prog/analysis.go
index f8330ed1c..519d5ba84 100644
--- a/prog/analysis.go
+++ b/prog/analysis.go
@@ -134,11 +134,9 @@ func foreachArgImpl(arg Arg, ctx ArgCtx, f func(Arg, *ArgCtx)) {
 		var totalSize uint64
 		for _, arg1 := range a.Inner {
 			foreachArgImpl(arg1, ctx, f)
-			if !arg1.Type().BitfieldMiddle() {
-				size := arg1.Size()
-				ctx.Offset += size
-				totalSize += size
-			}
+			size := arg1.Size()
+			ctx.Offset += size
+			totalSize += size
 		}
 		claimedSize := a.Size()
 		varlen := a.Type().Varlen()
diff --git a/prog/any.go b/prog/any.go
index 3f0cb4825..582f00195 100644
--- a/prog/any.go
+++ b/prog/any.go
@@ -331,9 +331,7 @@ func (target *Target) squashGroup(arg *GroupArg, elems *[]Arg) {
 	if typ, ok := arg.Type().(*StructType); ok && typ.Varlen() && typ.AlignAttr != 0 {
 		var fieldsSize uint64
 		for _, fld := range arg.Inner {
-			if !fld.Type().BitfieldMiddle() {
-				fieldsSize += fld.Size()
-			}
+			fieldsSize += fld.Size()
 		}
 		if fieldsSize%typ.AlignAttr != 0 {
 			pad = typ.AlignAttr - fieldsSize%typ.AlignAttr
@@ -342,7 +340,8 @@ func (target *Target) squashGroup(arg *GroupArg, elems *[]Arg) {
 	var bitfield uint64
 	for _, fld := range arg.Inner {
 		// Squash bitfields separately.
-		if bfLen := fld.Type().BitfieldLength(); bfLen != 0 {
+		if fld.Type().IsBitfield() {
+			bfLen := fld.Type().BitfieldLength()
 			bfOff := fld.Type().BitfieldOffset()
 			// Note: we can have a ResultArg here as well,
 			// but it is unsupported at the moment.
@@ -351,7 +350,7 @@ func (target *Target) squashGroup(arg *GroupArg, elems *[]Arg) {
 				panic(fmt.Sprintf("bitfield has bad format %v", bf))
 			}
 			bitfield |= (v & ((1 << bfLen) - 1)) << bfOff
-			if !fld.Type().BitfieldMiddle() {
+			if fld.Size() != 0 {
 				elem := target.ensureDataElem(elems)
 				for i := uint64(0); i < fld.Size(); i++ {
 					elem.data = append(elem.Data(), byte(bitfield))
@@ -370,8 +369,9 @@ func (target *Target) squashGroup(arg *GroupArg, elems *[]Arg) {
 }
 
 func (target *Target) squashedValue(arg *ConstArg) (uint64, BinaryFormat) {
-	bf := arg.Type().Format()
-	if _, ok := arg.Type().(*CsumType); ok {
+	typ := arg.Type()
+	bf := typ.Format()
+	if _, ok := typ.(*CsumType); ok {
 		// We can't compute value for the checksum here,
 		// but at least leave something recognizable by hints code.
 		// TODO: hints code won't recognize this, because it won't find
@@ -383,7 +383,7 @@ func (target *Target) squashedValue(arg *ConstArg) (uint64, BinaryFormat) {
 	v, _ := arg.Value()
 	if bf == FormatBigEndian {
 		bf = FormatNative
-		switch arg.Size() {
+		switch typ.UnitSize() {
 		case 2:
 			v = uint64(swap16(uint16(v)))
 		case 4:
diff --git a/prog/encodingexec.go b/prog/encodingexec.go
index 2d2f02e57..2e69f2116 100644
--- a/prog/encodingexec.go
+++ b/prog/encodingexec.go
@@ -133,7 +133,7 @@ func (w *execContext) writeCopyin(c *Call) {
 			return
 		}
 		typ := arg.Type()
-		if typ.Dir() == DirOut || IsPad(typ) || arg.Size() == 0 {
+		if typ.Dir() == DirOut || IsPad(typ) || (arg.Size() == 0 && !typ.IsBitfield()) {
 			return
 		}
 		w.write(execInstrCopyin)
@@ -236,7 +236,7 @@ func (w *execContext) writeArg(arg Arg) {
 	case *ConstArg:
 		val, pidStride := a.Value()
 		typ := a.Type()
-		w.writeConstArg(a.Size(), val, typ.BitfieldOffset(), typ.BitfieldLength(), pidStride, typ.Format())
+		w.writeConstArg(typ.UnitSize(), val, typ.BitfieldOffset(), typ.BitfieldLength(), pidStride, typ.Format())
 	case *ResultArg:
 		if a.Res == nil {
 			w.writeConstArg(a.Size(), a.Val, 0, 0, 0, a.Type().Format())
diff --git a/prog/prog.go b/prog/prog.go
index 83e5991d8..575f0da9b 100644
--- a/prog/prog.go
+++ b/prog/prog.go
@@ -193,9 +193,7 @@ func (arg *GroupArg) Size() uint64 {
 	case *StructType:
 		var size uint64
 		for _, fld := range arg.Inner {
-			if !fld.Type().BitfieldMiddle() {
-				size += fld.Size()
-			}
+			size += fld.Size()
 		}
 		if typ.AlignAttr != 0 && size%typ.AlignAttr != 0 {
 			size += typ.AlignAttr - size%typ.AlignAttr
diff --git a/prog/size.go b/prog/size.go
index 0f3435bbd..2ebf9fc29 100644
--- a/prog/size.go
+++ b/prog/size.go
@@ -45,9 +45,7 @@ func (target *Target) assignSize(dst *ConstArg, pos Arg, path []string, args []A
 	var offset uint64
 	for _, buf := range args {
 		if elem != buf.Type().FieldName() {
-			if !buf.Type().BitfieldMiddle() {
-				offset += buf.Size()
-			}
+			offset += buf.Size()
 			continue
 		}
 		buf = InnerArg(buf)
diff --git a/prog/types.go b/prog/types.go
index 2eec68a4d..6b2d37e07 100644
--- a/prog/types.go
+++ b/prog/types.go
@@ -60,7 +60,11 @@ type Type interface {
 	Format() BinaryFormat
 	BitfieldOffset() uint64
 	BitfieldLength() uint64
-	BitfieldMiddle() bool // returns true for all but last bitfield in a group
+	IsBitfield() bool
+	// For most of the types UnitSize is equal to Size.
+	// These are different only for all but last bitfield in the group,
+	// where Size == 0 and UnitSize equals to the underlying bitfield type size.
+	UnitSize() uint64
 
 	DefaultArg() Arg
 	isDefaultArg(arg Arg) bool
@@ -78,9 +82,10 @@ func IsPad(t Type) bool {
 }
 
 type TypeCommon struct {
-	TypeName   string
-	FldName    string // for struct fields and named args
-	TypeSize   uint64 // static size of the type, or 0 for variable size types
+	TypeName string
+	FldName  string // for struct fields and named args
+	// Static size of the type, or 0 for variable size types and all but last bitfields in the group.
+	TypeSize   uint64
 	ArgDir     Dir
 	IsOptional bool
 	IsVarlen   bool
@@ -125,7 +130,11 @@ func (t *TypeCommon) BitfieldLength() uint64 {
 	return 0
 }
 
-func (t *TypeCommon) BitfieldMiddle() bool {
+func (t *TypeCommon) UnitSize() uint64 {
+	return t.Size()
+}
+
+func (t *TypeCommon) IsBitfield() bool {
 	return false
 }
 
@@ -180,10 +189,10 @@ func (t *ResourceType) Format() BinaryFormat {
 
 type IntTypeCommon struct {
 	TypeCommon
-	ArgFormat   BinaryFormat
-	BitfieldOff uint64
-	BitfieldLen uint64
-	BitfieldMdl bool
+	ArgFormat    BinaryFormat
+	BitfieldOff  uint64
+	BitfieldLen  uint64
+	BitfieldUnit uint64
 }
 
 func (t *IntTypeCommon) String() string {
@@ -215,8 +224,15 @@ func (t *IntTypeCommon) BitfieldLength() uint64 {
 	return t.BitfieldLen
 }
 
-func (t *IntTypeCommon) BitfieldMiddle() bool {
-	return t.BitfieldMdl
+func (t *IntTypeCommon) UnitSize() uint64 {
+	if t.BitfieldLen != 0 {
+		return t.BitfieldUnit
+	}
+	return t.Size()
+}
+
+func (t *IntTypeCommon) IsBitfield() bool {
+	return t.BitfieldLen != 0
 }
 
 type ConstType struct {