cmd/6g: extend componentgen to small arrays and structs.

Fixes #4092.

R=golang-dev, dave, rsc
CC=golang-dev
https://golang.org/cl/6819083

src/cmd/6g/cgen.c

@@ -1458,6 +1458,8 @@ cadable(Node *n)
 /*
  * copy a composite value by moving its individual components.
  * Slices, strings and interfaces are supported.
+ * Small structs or arrays with elements of basic type are
+ * also supported.
  * nr is N when assigning a zero value.
  * return 1 if can do, 0 if cant.
  */
@@ -1465,7 +1467,10 @@ int
 componentgen(Node *nr, Node *nl)
 {
 	Node nodl, nodr;
+	Type *t;
 	int freel, freer;
+	vlong fldcount;
+	vlong loffset, roffset;
 
 	freel = 0;
 	freer = 0;
@@ -1475,8 +1480,33 @@ componentgen(Node *nr, Node *nl)
 		goto no;
 
 	case TARRAY:
-		if(!isslice(nl->type))
+		t = nl->type;
+
+		// Slices are ok.
+		if(isslice(t))
+			break;
+		// Small arrays are ok.
+		if(t->bound > 0 && t->bound <= 3 && !isfat(t->type))
+			break;
+
+		goto no;
+
+	case TSTRUCT:
+		// Small structs with non-fat types are ok.
+		// Zero-sized structs are treated separately elsewhere.
+		fldcount = 0;
+		for(t=nl->type->type; t; t=t->down) {
+			if(isfat(t->type))
+				goto no;
+			if(t->etype != TFIELD)
+				fatal("componentgen: not a TFIELD: %lT", t);
+			fldcount++;
+		}
+		if(fldcount == 0 || fldcount > 3)
 			goto no;
+
+		break;
+
 	case TSTRING:
 	case TINTER:
 		break;
@@ -1500,6 +1530,23 @@ componentgen(Node *nr, Node *nl)
 
 	switch(nl->type->etype) {
 	case TARRAY:
+		// componentgen for arrays.
+		t = nl->type;
+		if(!isslice(t)) {
+			nodl.type = t->type;
+			nodr.type = nodl.type;
+			for(fldcount=0; fldcount < t->bound; fldcount++) {
+				if(nr == N)
+					clearslim(&nodl);
+				else
+					gmove(&nodr, &nodl);
+				nodl.xoffset += t->type->width;
+				nodr.xoffset += t->type->width;
+			}
+			goto yes;
+		}
+
+		// componentgen for slices.
 		nodl.xoffset += Array_array;
 		nodl.type = ptrto(nl->type->type);
 
@@ -1577,6 +1624,23 @@ componentgen(Node *nr, Node *nl)
 		gmove(&nodr, &nodl);
 
 		goto yes;
+
+	case TSTRUCT:
+		loffset = nodl.xoffset;
+		roffset = nodr.xoffset;
+		for(t=nl->type->type; t; t=t->down) {
+			nodl.xoffset = loffset + t->width;
+			nodl.type = t->type;
+
+			if(nr == N)
+				clearslim(&nodl);
+			else {
+				nodr.xoffset = roffset + t->width;
+				nodr.type = nodl.type;
+				gmove(&nodr, &nodl);
+			}
+		}
+		goto yes;
 	}
 
 no:

src/cmd/6g/gg.h

@@ -79,6 +79,7 @@ void	allocparams(void);
 void	checklabels();
 void	ginscall(Node*, int);
 int	gen_as_init(Node*);
+void	clearslim(Node*);
 
 /*
  * cgen.c

src/cmd/gc/gen.c

@@ -632,6 +632,67 @@ cgen_discard(Node *nr)
 	}
 }
 
+/*
+ * clearslim generates code to zero a slim node.
+ */
+void
+clearslim(Node *n)
+{
+	Node z;
+	Mpflt zero;
+
+	memset(&z, 0, sizeof(z));
+	z.op = OLITERAL;
+	z.type = n->type;
+	z.addable = 1;
+
+	switch(simtype[n->type->etype]) {
+	case TCOMPLEX64:
+	case TCOMPLEX128:
+		z.val.u.cval = mal(sizeof(z.val.u.cval));
+		mpmovecflt(&z.val.u.cval->real, 0.0);
+		mpmovecflt(&z.val.u.cval->imag, 0.0);
+		break;
+
+	case TFLOAT32:
+	case TFLOAT64:
+		mpmovecflt(&zero, 0.0);
+		z.val.ctype = CTFLT;
+		z.val.u.fval = &zero;
+		break;
+
+	case TPTR32:
+	case TPTR64:
+	case TCHAN:
+	case TMAP:
+		z.val.ctype = CTNIL;
+		break;
+
+	case TBOOL:
+		z.val.ctype = CTBOOL;
+		break;
+
+	case TINT8:
+	case TINT16:
+	case TINT32:
+	case TINT64:
+	case TUINT8:
+	case TUINT16:
+	case TUINT32:
+	case TUINT64:
+		z.val.ctype = CTINT;
+		z.val.u.xval = mal(sizeof(z.val.u.xval));
+		mpmovecfix(z.val.u.xval, 0);
+		break;
+
+	default:
+		fatal("clearslim called on type %T", n->type);
+	}
+
+	ullmancalc(&z);
+	cgen(&z, n);
+}
+
 /*
  * generate assignment:
  *	nl = nr
@@ -640,9 +701,7 @@ cgen_discard(Node *nr)
 void
 cgen_as(Node *nl, Node *nr)
 {
-	Node nc;
 	Type *tl;
-	int iszer;
 
 	if(debug['g']) {
 		dump("cgen_as", nl);
@@ -657,7 +716,6 @@ cgen_as(Node *nl, Node *nr)
 		return;
 	}
 
-	iszer = 0;
 	if(nr == N || isnil(nr)) {
 		// externals and heaps should already be clear
 		if(nr == N) {
@@ -672,59 +730,12 @@ cgen_as(Node *nl, Node *nr)
 			return;
 		if(isfat(tl)) {
 			clearfat(nl);
-			goto ret;
-		}
-
-		/* invent a "zero" for the rhs */
-		iszer = 1;
-		nr = &nc;
-		memset(nr, 0, sizeof(*nr));
-		switch(simtype[tl->etype]) {
-		default:
-			fatal("cgen_as: tl %T", tl);
-			break;
-
-		case TINT8:
-		case TUINT8:
-		case TINT16:
-		case TUINT16:
-		case TINT32:
-		case TUINT32:
-		case TINT64:
-		case TUINT64:
-			nr->val.u.xval = mal(sizeof(*nr->val.u.xval));
-			mpmovecfix(nr->val.u.xval, 0);
-			nr->val.ctype = CTINT;
-			break;
-
-		case TFLOAT32:
-		case TFLOAT64:
-			nr->val.u.fval = mal(sizeof(*nr->val.u.fval));
-			mpmovecflt(nr->val.u.fval, 0.0);
-			nr->val.ctype = CTFLT;
-			break;
-
-		case TBOOL:
-			nr->val.u.bval = 0;
-			nr->val.ctype = CTBOOL;
-			break;
-
-		case TPTR32:
-		case TPTR64:
-			nr->val.ctype = CTNIL;
-			break;
-
-		case TCOMPLEX64:
-		case TCOMPLEX128:
-			nr->val.u.cval = mal(sizeof(*nr->val.u.cval));
-			mpmovecflt(&nr->val.u.cval->real, 0.0);
-			mpmovecflt(&nr->val.u.cval->imag, 0.0);
-			break;
+			return;
 		}
-		nr->op = OLITERAL;
-		nr->type = tl;
-		nr->addable = 1;
-		ullmancalc(nr);
+		clearslim(nl);
+		if(nl->addable)
+			gused(nl);
+		return;
 	}
 
 	tl = nl->type;
@@ -732,11 +743,6 @@ cgen_as(Node *nl, Node *nr)
 		return;
 
 	cgen(nr, nl);
-	if(iszer && nl->addable)
-		gused(nl);
-
-ret:
-	;
 }
 
 /*