cmd/gc: do not generate code for var _ = ... unless necessary

Fixes #2443.

R=ken2
CC=golang-dev
https://golang.org/cl/6997048

diff --git a/src/cmd/gc/go.h b/src/cmd/gc/go.h
index 071422367c5cdc3ba0b9e5d603d107dc5b938f95..accb19cd99dfb851939143455ddb2df8c8f2f9e9 100644 (file)
--- a/src/cmd/gc/go.h
+++ b/src/cmd/gc/go.h
@@ -1375,6 +1375,7 @@ void      walkexprlistsafe(NodeList *l, NodeList **init);
 void   walkstmt(Node **np);
 void   walkstmtlist(NodeList *l);
 Node*  conv(Node*, Type*);
+int    candiscard(Node*);
 
 /*
  *     arch-specific ggen.c/gsubr.c/gobj.c/pgen.c

diff --git a/src/cmd/gc/init.c b/src/cmd/gc/init.c
index be402cc0cec3f566822eb5cc7823d8d933f77bd4..918d37180b5f35d424283815be1a9329805007de 100644 (file)
--- a/src/cmd/gc/init.c
+++ b/src/cmd/gc/init.c
@@ -55,6 +55,10 @@ anyinit(NodeList *n)
                case ODCLTYPE:
                case OEMPTY:
                        break;
+               case OAS:
+                       if(isblank(l->n->left) && candiscard(l->n->right))
+                               break;
+                       // fall through
                default:
                        return 1;
                }

diff --git a/src/cmd/gc/sinit.c b/src/cmd/gc/sinit.c
index e8010099d211e60cf1d034e4c50be172d4562306..e1a0758da17496f0f2836e45e187c702872fec35 100644 (file)
--- a/src/cmd/gc/sinit.c
+++ b/src/cmd/gc/sinit.c
@@ -108,6 +108,13 @@ init1(Node *n, NodeList **out)
                case OAS:
                        if(n->defn->left != n)
                                goto bad;
+                       if(isblank(n->defn->left) && candiscard(n->defn->right)) {
+                               n->defn->op = OEMPTY;
+                               n->defn->left = N;
+                               n->defn->right = N;
+                               break;
+                       }
+
                /*
                        n->defn->dodata = 1;
                        init1(n->defn->right, out);

diff --git a/src/cmd/gc/walk.c b/src/cmd/gc/walk.c
index 98b2a4fa74421758a9bbe9533f5b2edaa03eae5b..3a2152b0924a9a18cb78ed466a0177397a542035 100644 (file)
--- a/src/cmd/gc/walk.c
+++ b/src/cmd/gc/walk.c
@@ -183,8 +183,8 @@ walkstmt(Node **np)
                dump("nottop", n);
                break;
 
-       case OASOP:
        case OAS:
+       case OASOP:
        case OAS2:
        case OAS2DOTTYPE:
        case OAS2RECV:
@@ -3226,3 +3226,112 @@ usefield(Node *n)
        curfn->paramfld = l;
 }
 
+static int
+candiscardlist(NodeList *l)
+{
+       for(; l; l=l->next)
+               if(!candiscard(l->n))
+                       return 0;
+       return 1;
+}
+
+int
+candiscard(Node *n)
+{
+       if(n == N)
+               return 1;
+       
+       switch(n->op) {
+       default:
+               return 0;
+
+       case ONAME:
+       case ONONAME:
+       case OTYPE:
+       case OPACK:
+       case OLITERAL:
+       case OADD:
+       case OSUB:
+       case OOR:
+       case OXOR:
+       case OADDSTR:
+       case OADDR:
+       case OANDAND:
+       case OARRAYBYTESTR:
+       case OARRAYRUNESTR:
+       case OSTRARRAYBYTE:
+       case OSTRARRAYRUNE:
+       case OCAP:
+       case OCMPIFACE:
+       case OCMPSTR:
+       case OCOMPLIT:
+       case OMAPLIT:
+       case OSTRUCTLIT:
+       case OARRAYLIT:
+       case OPTRLIT:
+       case OCONV:
+       case OCONVIFACE:
+       case OCONVNOP:
+       case ODOT:
+       case OEQ:
+       case ONE:
+       case OLT:
+       case OLE:
+       case OGT:
+       case OGE:
+       case OKEY:
+       case OLEN:
+       case OMUL:
+       case OLSH:
+       case ORSH:
+       case OAND:
+       case OANDNOT:
+       case ONEW:
+       case ONOT:
+       case OCOM:
+       case OPLUS:
+       case OMINUS:
+       case OOROR:
+       case OPAREN:
+       case ORUNESTR:
+       case OREAL:
+       case OIMAG:
+       case OCOMPLEX:
+               // Discardable as long as the subpieces are.
+               break;
+
+       case ODIV:
+       case OMOD:
+               // Discardable as long as we know it's not division by zero.
+               if(isconst(n->right, CTINT) && mpcmpfixc(n->right->val.u.xval, 0) != 0)
+                       break;
+               if(isconst(n->right, CTFLT) && mpcmpfltc(n->right->val.u.fval, 0) != 0)
+                       break;
+               return 0;
+
+       case OMAKECHAN:
+       case OMAKEMAP:
+               // Discardable as long as we know it won't fail because of a bad size.
+               if(isconst(n->left, CTINT) && mpcmpfixc(n->left->val.u.xval, 0) == 0)
+                       break;
+               return 0;
+       
+       case OMAKESLICE:
+               // Difficult to tell what sizes are okay.
+               return 0;               
+       }
+       
+       if(!candiscard(n->left) ||
+          !candiscard(n->right) ||
+          !candiscard(n->ntest) ||
+          !candiscard(n->nincr) ||
+          !candiscardlist(n->ninit) ||
+          !candiscardlist(n->nbody) ||
+          !candiscardlist(n->nelse) ||
+          !candiscardlist(n->list) ||
+          !candiscardlist(n->rlist)) {
+               return 0;
+       }
+       
+       return 1;
+}

diff --git a/test/golden.out b/test/golden.out
index 3e44e04c6aae814feb2f6c250598009124f92699..742a5d3f6344c4d42a004a83abbd80e9415f6efd 100644 (file)
--- a/test/golden.out
+++ b/test/golden.out
@@ -16,13 +16,9 @@
 == fixedbugs/
 
 =========== fixedbugs/bug429.go
-throw: all goroutines are asleep - deadlock!
+fatal error: all goroutines are asleep - deadlock!
 
 == bugs/
 
 =========== bugs/bug395.go
 bug395 is broken
-
-=========== bugs/bug434.go
-bugs/bug434.dir/two.go:10: one.t.int undefined (cannot refer to unexported field or method one.int)
-BUG:bug434

diff --git a/test/sinit.go b/test/sinit.go
index ffb8ef75110b4e280a0f76a66c7ca82ca5866a82..5e50e1100a873754d69f20c1b8ee33ced287efc7 100644 (file)
--- a/test/sinit.go
+++ b/test/sinit.go
@@ -259,3 +259,13 @@ var copy_pt0a = pt0a
 var copy_pt0b = pt0b
 var copy_pt1 = pt1
 var copy_pt1a = pt1a
+
+var _ interface{} = 1
+
+type T1 int
+
+func (t *T1) M() {}
+
+type Mer interface { M() }
+
+var _ Mer = (*T1)(nil)