1 files changed, 35 insertions, 26 deletions

diff --git a/src/cmd/6g/ggen.c b/src/cmd/6g/ggen.c
index 9665d831b..363620769 100644
--- a/src/cmd/6g/ggen.c
+++ b/src/cmd/6g/ggen.c
@@ -175,7 +175,6 @@ fixautoused(Prog *p)
 void
 ginscall(Node *f, int proc)
 {
-	int32 arg;
 	Prog *p;
 	Node reg, con;
 	Node r1;
@@ -183,21 +182,6 @@ ginscall(Node *f, int proc)
 	if(f->type != T)
 		setmaxarg(f->type);
 
-	arg = -1;
-	// Most functions have a fixed-size argument block, so traceback uses that during unwind.
-	// Not all, though: there are some variadic functions in package runtime,
-	// and for those we emit call-specific metadata recorded by caller.
-	// Reflect generates functions with variable argsize (see reflect.methodValueCall/makeFuncStub),
-	// so we do this for all indirect calls as well.
-	if(f->type != T && (f->sym == S || (f->sym != S && f->sym->pkg == runtimepkg) || proc == 1 || proc == 2)) {
-		arg = f->type->argwid;
-		if(proc == 1 || proc == 2)
-			arg += 2*widthptr;
-	}
-
-	if(arg != -1)
-		gargsize(arg);
-
 	switch(proc) {
 	default:
 		fatal("ginscall: bad proc %d", proc);
@@ -275,9 +259,6 @@ ginscall(Node *f, int proc)
 		}
 		break;
 	}
-
-	if(arg != -1)
-		gargsize(-1);
 }
 
 /*
@@ -1121,26 +1102,54 @@ clearfat(Node *nl)
 	c = w % 8;	// bytes
 	q = w / 8;	// quads
 
+	if(q < 4) {
+		// Write sequence of MOV 0, off(base) instead of using STOSQ.
+		// The hope is that although the code will be slightly longer,
+		// the MOVs will have no dependencies and pipeline better
+		// than the unrolled STOSQ loop.
+		// NOTE: Must use agen, not igen, so that optimizer sees address
+		// being taken. We are not writing on field boundaries.
+		agenr(nl, &n1, N);
+		n1.op = OINDREG;
+		nodconst(&z, types[TUINT64], 0);
+		while(q-- > 0) {
+			n1.type = z.type;
+			gins(AMOVQ, &z, &n1);
+			n1.xoffset += 8;
+		}
+		if(c >= 4) {
+			nodconst(&z, types[TUINT32], 0);
+			n1.type = z.type;
+			gins(AMOVL, &z, &n1);
+			n1.xoffset += 4;
+			c -= 4;
+		}
+		nodconst(&z, types[TUINT8], 0);
+		while(c-- > 0) {
+			n1.type = z.type;
+			gins(AMOVB, &z, &n1);
+			n1.xoffset++;
+		}
+		regfree(&n1);
+		return;
+	}
+
 	savex(D_DI, &n1, &oldn1, N, types[tptr]);
 	agen(nl, &n1);
 
 	savex(D_AX, &ax, &oldax, N, types[tptr]);
 	gconreg(AMOVL, 0, D_AX);
 
-	if(q > 128 || (q >= 4 && nacl)) {
+	if(q > 128 || nacl) {
 		gconreg(movptr, q, D_CX);
 		gins(AREP, N, N);	// repeat
 		gins(ASTOSQ, N, N);	// STOQ AL,*(DI)+
-	} else if(q >= 4) {
+	} else {
 		p = gins(ADUFFZERO, N, N);
 		p->to.type = D_ADDR;
 		p->to.sym = linksym(pkglookup("duffzero", runtimepkg));
-		// 2 and 128 = magic constants: see ../../pkg/runtime/asm_amd64.s
+		// 2 and 128 = magic constants: see ../../runtime/asm_amd64.s
 		p->to.offset = 2*(128-q);
-	} else
-	while(q > 0) {
-		gins(ASTOSQ, N, N);	// STOQ AL,*(DI)+
-		q--;
 	}
 
 	z = ax;