cmd/gc: handle variable initialization by block move in liveness

Any initialization of a variable by a block copy or block zeroing
or by multiple assignments (componentwise copying or zeroing
of a multiword variable) needs to emit a VARDEF. These cases were not.

Fixes #7205.

TBR=iant
CC=golang-codereviews
https://golang.org/cl/63650044

src/cmd/5g/cgen.c

@@ -1414,6 +1414,7 @@ sgen(Node *n, Node *res, int64 w)
 	int32 c, odst, osrc;
 	int dir, align, op;
 	Prog *p, *ploop;
+	NodeList *l;
 
 	if(debug['g']) {
 		print("\nsgen w=%lld\n", w);
@@ -1439,6 +1440,17 @@ sgen(Node *n, Node *res, int64 w)
 		return;
 	}
 
+	// Record site of definition of ns for liveness analysis.
+	if(res->op == ONAME && res->class != PEXTERN)
+		gvardef(res);
+	
+	// If copying .args, that's all the results, so record definition sites
+	// for them for the liveness analysis.
+	if(res->op == ONAME && strcmp(res->sym->name, ".args") == 0)
+		for(l = curfn->dcl; l != nil; l = l->next)
+			if(l->n->class == PPARAMOUT)
+				gvardef(l->n);
+
 	// Avoid taking the address for simple enough types.
 	if(componentgen(n, res))
 		return;

src/cmd/6g/cgen.c

@@ -1337,6 +1337,7 @@ sgen(Node *n, Node *ns, int64 w)
 {
 	Node nodl, nodr, nodsi, noddi, cx, oldcx, tmp;
 	vlong c, q, odst, osrc;
+	NodeList *l;
 
 	if(debug['g']) {
 		print("\nsgen w=%lld\n", w);
@@ -1349,6 +1350,17 @@ sgen(Node *n, Node *ns, int64 w)
 
 	if(w < 0)
 		fatal("sgen copy %lld", w);
+	
+	// Record site of definition of ns for liveness analysis.
+	if(ns->op == ONAME && ns->class != PEXTERN)
+		gvardef(ns);
+	
+	// If copying .args, that's all the results, so record definition sites
+	// for them for the liveness analysis.
+	if(ns->op == ONAME && strcmp(ns->sym->name, ".args") == 0)
+		for(l = curfn->dcl; l != nil; l = l->next)
+			if(l->n->class == PPARAMOUT)
+				gvardef(l->n);
 
 	// Avoid taking the address for simple enough types.
 	if(componentgen(n, ns))

src/cmd/8g/cgen.c

@@ -1203,6 +1203,7 @@ sgen(Node *n, Node *res, int64 w)
 {
 	Node dst, src, tdst, tsrc;
 	int32 c, q, odst, osrc;
+	NodeList *l;
 
 	if(debug['g']) {
 		print("\nsgen w=%lld\n", w);
@@ -1223,6 +1224,17 @@ sgen(Node *n, Node *res, int64 w)
 		return;
 	}
 
+	// Record site of definition of ns for liveness analysis.
+	if(res->op == ONAME && res->class != PEXTERN)
+		gvardef(res);
+	
+	// If copying .args, that's all the results, so record definition sites
+	// for them for the liveness analysis.
+	if(res->op == ONAME && strcmp(res->sym->name, ".args") == 0)
+		for(l = curfn->dcl; l != nil; l = l->next)
+			if(l->n->class == PPARAMOUT)
+				gvardef(l->n);
+
 	// Avoid taking the address for simple enough types.
 	if(componentgen(n, res))
 		return;

src/cmd/gc/pgen.c

@@ -34,8 +34,8 @@ makefuncdatasym(char *namefmt, int64 funcdatakind)
 void
 gvardef(Node *n)
 {
-	if(n == N || !isfat(n->type))
+	if(n == N)
-		fatal("gvardef: node is not fat");
+		fatal("gvardef nil");
 	switch(n->class) {
 	case PAUTO:
 	case PPARAM:

src/cmd/gc/plive.c

@@ -621,7 +621,7 @@ freecfg(Array *cfg)
 static int
 isfunny(Node *node)
 {
-	char *names[] = { ".fp", ".args", "_", nil };
+	char *names[] = { ".fp", ".args", nil };
 	int i;
 
 	if(node->sym != nil && node->sym->name != nil)
@@ -696,8 +696,8 @@ progeffects(Prog *prog, Array *vars, Bvec *uevar, Bvec *varkill, Bvec *avarinit)
 	}
 	if(info.flags & (LeftRead | LeftWrite | LeftAddr)) {
 		from = &prog->from;
-		if (from->node != nil && !isfunny(from->node) && from->sym != nil) {
+		if (from->node != nil && from->sym != nil) {
-			switch(prog->from.node->class & ~PHEAP) {
+			switch(from->node->class & ~PHEAP) {
 			case PAUTO:
 			case PPARAM:
 			case PPARAMOUT:
@@ -710,7 +710,7 @@ progeffects(Prog *prog, Array *vars, Bvec *uevar, Bvec *varkill, Bvec *avarinit)
 					if(info.flags & (LeftRead | LeftAddr))
 						bvset(uevar, pos);
 					if(info.flags & LeftWrite)
-						if(from->node != nil && (!isfat(from->node->type) || prog->as == AVARDEF))
+						if(from->node != nil && !isfat(from->node->type))
 							bvset(varkill, pos);
 				}
 			}
@@ -719,8 +719,8 @@ progeffects(Prog *prog, Array *vars, Bvec *uevar, Bvec *varkill, Bvec *avarinit)
 Next:
 	if(info.flags & (RightRead | RightWrite | RightAddr)) {
 		to = &prog->to;
-		if (to->node != nil && to->sym != nil && !isfunny(to->node)) {
+		if (to->node != nil && to->sym != nil) {
-			switch(prog->to.node->class & ~PHEAP) {
+			switch(to->node->class & ~PHEAP) {
 			case PAUTO:
 			case PPARAM:
 			case PPARAMOUT:
@@ -728,10 +728,9 @@ Next:
 				if(pos == -1)
 					goto Next1;
 				if(to->node->addrtaken) {
-					//if(prog->as == AKILL)
+					bvset(avarinit, pos);
-					//	bvset(varkill, pos);
+					if(prog->as == AVARDEF)
-					//else
+						bvset(varkill, pos);
-						bvset(avarinit, pos);
 				} else {
 					if(info.flags & (RightRead | RightAddr))
 						bvset(uevar, pos);

test/live.go

@@ -95,3 +95,21 @@ func f7() (x string) {
 	return
 }
 
+// ignoring block returns used to cause "live at entry to f8: x, y".
+
+func f8() (x, y string) {
+	return g8()
+}
+
+func g8() (string, string)
+
+// ignoring block assignments used to cause "live at entry to f9: x"
+// issue 7205
+
+var i9 interface{}
+
+func f9() bool {
+	g8()
+	x := i9
+	return x != 99
+}