5g: defer vs optimizer bug

Fixes #1924.

R=ken2
CC=golang-dev
https://golang.org/cl/4802063

src/cmd/5g/reg.c

@@ -728,13 +728,19 @@ addsplits(void)
 void
 addmove(Reg *r, int bn, int rn, int f)
 {
-	Prog *p, *p1;
+	Prog *p, *p1, *p2;
 	Adr *a;
 	Var *v;
 
 	p1 = mal(sizeof(*p1));
 	*p1 = zprog;
 	p = r->prog;
+	
+	// If there's a stack fixup coming (after BL newproc or BL deferproc),
+	// delay the load until after the fixup.
+	p2 = p->link;
+	if(p2 && p2->as == AMOVW && p2->from.type == D_CONST && p2->from.reg == REGSP && p2->to.reg == REGSP && p2->to.type == D_REG)
+		p = p2;
 
 	p1->link = p->link;
 	p->link = p1;

test/fixedbugs/bug364.go

+package main
+
+import "fmt"
+
+var s string
+
+func accum(args ...interface{}) {
+	s += fmt.Sprintln(args...)
+}
+
+func f(){
+	v := 0.0
+	for i := 0; i < 3; i++ {
+		v += 0.1
+		defer accum(v)
+	}
+}
+
+func main() {
+	f()
+	if s != "0.30000000000000004\n0.2\n0.1\n" {
+		println("BUG: defer")
+		print(s)
+	}
+}