compiler, reflect, runtime: remove zero field from type descriptor

    
    Type descriptors picked up a zero field because the gc map
    implementation used it.  However, it's since been dropped by the gc
    library.  It was never used by gccgo.  Drop it now in preparation for
    upgrading to the Go 1.5 library.
    
    Reviewed-on: https://go-review.googlesource.com/16486


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@229546 138bc75d-0d04-0410-961f-82ee72b054a4

8 files changed, 7 insertions, 143 deletions

diff --git a/gcc/go/gofrontend/MERGE b/gcc/go/gofrontend/MERGE
index 8d3547b3295..987bd684c59 100644
--- a/gcc/go/gofrontend/MERGE
+++ b/gcc/go/gofrontend/MERGE
@@ -1,4 +1,4 @@
-57da43e8159bfe1a31e49683c371cf36e2fb6051
+85994dd0a88d1b24b2ddfc9c9ab22ee16c9e8b54
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.
diff --git a/gcc/go/gofrontend/gogo.cc b/gcc/go/gofrontend/gogo.cc
index 363fd5cff18..6708be93cf7 100644
--- a/gcc/go/gofrontend/gogo.cc
+++ b/gcc/go/gofrontend/gogo.cc
@@ -42,9 +42,6 @@ Gogo::Gogo(Backend* backend, Linemap* linemap, int, int pointer_size)
     pkgpath_(),
     pkgpath_symbol_(),
     prefix_(),
-    zero_value_(NULL),
-    zero_value_size_(0),
-    zero_value_align_(0),
     pkgpath_set_(false),
     pkgpath_from_option_(false),
     prefix_from_option_(false),
@@ -638,87 +635,6 @@ Gogo::current_bindings() const
     return this->globals_;
 }
 
-// Return the special variable used as the zero value of types.
-
-Named_object*
-Gogo::zero_value(Type *type)
-{
-  if (this->zero_value_ == NULL)
-    {
-      Location bloc = Linemap::predeclared_location();
-
-      // We will change the type later, when we know the size.
-      Type* byte_type = this->lookup_global("byte")->type_value();
-
-      Expression* zero = Expression::make_integer_ul(0, NULL, bloc);
-      Type* array_type = Type::make_array_type(byte_type, zero);
-
-      Variable* var = new Variable(array_type, NULL, true, false, false, bloc);
-      this->zero_value_ = Named_object::make_variable("go$zerovalue", NULL,
-						      var);
-    }
-
-  // The zero value will be the maximum required size.
-  int64_t size;
-  bool ok = type->backend_type_size(this, &size);
-  if (!ok) {
-    go_assert(saw_errors());
-    size = 4;
-  }
-  if (size > this->zero_value_size_)
-    this->zero_value_size_ = size;
-
-  int64_t align;
-  ok = type->backend_type_align(this, &align);
-  if (!ok) {
-    go_assert(saw_errors());
-    align = 4;
-  }
-  if (align > this->zero_value_align_)
-    this->zero_value_align_ = align;
-
-  return this->zero_value_;
-}
-
-// Return whether V is the zero value variable.
-
-bool
-Gogo::is_zero_value(Variable* v) const
-{
-  return this->zero_value_ != NULL && this->zero_value_->var_value() == v;
-}
-
-// Return the backend variable for the special zero value, or NULL if
-// it is not needed.
-
-Bvariable*
-Gogo::backend_zero_value()
-{
-  if (this->zero_value_ == NULL)
-    return NULL;
-
-  Type* byte_type = this->lookup_global("byte")->type_value();
-  Btype* bbtype_type = byte_type->get_backend(this);
-
-  Type* int_type = this->lookup_global("int")->type_value();
-
-  Expression* e = Expression::make_integer_int64(this->zero_value_size_,
-						 int_type,
-						 Linemap::unknown_location());
-  Translate_context context(this, NULL, NULL, NULL);
-  Bexpression* blength = e->get_backend(&context);
-
-  Btype* barray_type = this->backend()->array_type(bbtype_type, blength);
-
-  std::string zname = this->zero_value_->name();
-  Bvariable* zvar =
-    this->backend()->implicit_variable(zname, barray_type, false,
-				       true, true, this->zero_value_align_);
-  this->backend()->implicit_variable_set_init(zvar, zname, barray_type,
-					      false, true, true, NULL);
-  return zvar;
-}
-
 // Add statements to INIT_STMTS which run the initialization
 // functions for imported packages.  This is only used for the "main"
 // package.
@@ -6534,9 +6450,7 @@ Variable::get_backend_variable(Gogo* gogo, Named_object* function,
 	  Btype* btype = type->get_backend(gogo);
 
 	  Bvariable* bvar;
-	  if (gogo->is_zero_value(this))
-	    bvar = gogo->backend_zero_value();
-	  else if (this->is_global_)
+	  if (this->is_global_)
 	    bvar = backend->global_variable((package == NULL
 					     ? gogo->package_name()
 					     : package->package_name()),
diff --git a/gcc/go/gofrontend/gogo.h b/gcc/go/gofrontend/gogo.h
index 6333c834c35..0b1f8ef3ca3 100644
--- a/gcc/go/gofrontend/gogo.h
+++ b/gcc/go/gofrontend/gogo.h
@@ -653,20 +653,6 @@ class Gogo
   named_types_are_converted() const
   { return this->named_types_are_converted_; }
 
-  // Return the variable to use for the zero value of TYPE.  All types
-  // shared the same zero value, and we make sure that it is large
-  // enough.
-  Named_object*
-  zero_value(Type *type);
-
-  // Return whether a variable is the zero value variable.
-  bool
-  is_zero_value(Variable* v) const;
-
-  // Create the zero value variable.
-  Bvariable*
-  backend_zero_value();
-
   // Write out the global values.
   void
   write_globals();
@@ -821,12 +807,6 @@ class Gogo
   std::string pkgpath_symbol_;
   // The prefix to use for symbols, from the -fgo-prefix option.
   std::string prefix_;
-  // The special zero value variable.
-  Named_object* zero_value_;
-  // The size of the zero value variable.
-  int64_t zero_value_size_;
-  // The alignment of the zero value variable, in bytes.
-  int64_t zero_value_align_;
   // Whether pkgpath_ has been set.
   bool pkgpath_set_;
   // Whether an explicit package path was set by -fgo-pkgpath.
diff --git a/gcc/go/gofrontend/types.cc b/gcc/go/gofrontend/types.cc
index 5c8950a028b..b4620ff0c86 100644
--- a/gcc/go/gofrontend/types.cc
+++ b/gcc/go/gofrontend/types.cc
@@ -1529,7 +1529,7 @@ Type::make_type_descriptor_type()
       // The type descriptor type.
 
       Struct_type* type_descriptor_type =
-	Type::make_builtin_struct_type(12,
+	Type::make_builtin_struct_type(11,
 				       "kind", uint8_type,
 				       "align", uint8_type,
 				       "fieldAlign", uint8_type,
@@ -1541,8 +1541,7 @@ Type::make_type_descriptor_type()
 				       "string", pointer_string_type,
 				       "", pointer_uncommon_type,
 				       "ptrToThis",
-				       pointer_type_descriptor_type,
-				       "zero", unsafe_pointer_type);
+				       pointer_type_descriptor_type);
 
       Named_type* named = Type::make_builtin_named_type("commonType",
 							type_descriptor_type);
@@ -2074,15 +2073,6 @@ Type::type_descriptor_constructor(Gogo* gogo, int runtime_type_kind,
     }
 
   ++p;
-  go_assert(p->is_field_name("zero"));
-  Expression* z = Expression::make_var_reference(gogo->zero_value(this), bloc);
-  z = Expression::make_unary(OPERATOR_AND, z, bloc);
-  Type* void_type = Type::make_void_type();
-  Type* unsafe_pointer_type = Type::make_pointer_type(void_type);
-  z = Expression::make_cast(unsafe_pointer_type, z, bloc);
-  vals->push_back(z);
-
-  ++p;
   go_assert(p == fields->end());
 
   return Expression::make_struct_composite_literal(td_type, vals, bloc);
diff --git a/libgo/go/reflect/type.go b/libgo/go/reflect/type.go
index 61b195563b6..5cdfba55648 100644
--- a/libgo/go/reflect/type.go
+++ b/libgo/go/reflect/type.go
@@ -262,7 +262,6 @@ type rtype struct {
 	string        *string        // string form; unnecessary  but undeniably useful
 	*uncommonType                // (relatively) uncommon fields
 	ptrToThis     *rtype         // type for pointer to this type, if used in binary or has methods
-	zero          unsafe.Pointer // pointer to zero value
 }
 
 // Method on non-interface type
@@ -1129,7 +1128,6 @@ func (t *rtype) ptrTo() *rtype {
 
 	p.uncommonType = nil
 	p.ptrToThis = nil
-	p.zero = unsafe.Pointer(&make([]byte, p.size)[0])
 	p.elem = t
 
 	if t.kind&kindNoPointers != 0 {
@@ -1505,7 +1503,6 @@ func ChanOf(dir ChanDir, t Type) Type {
 	ch.elem = typ
 	ch.uncommonType = nil
 	ch.ptrToThis = nil
-	ch.zero = unsafe.Pointer(&make([]byte, ch.size)[0])
 
 	ch.gc = unsafe.Pointer(&chanGC{
 		width: ch.size,
@@ -1561,7 +1558,6 @@ func MapOf(key, elem Type) Type {
 	mt.elem = etyp
 	mt.uncommonType = nil
 	mt.ptrToThis = nil
-	mt.zero = unsafe.Pointer(&make([]byte, mt.size)[0])
 	// mt.gc = unsafe.Pointer(&ptrGC{
 	// 	width:  unsafe.Sizeof(uintptr(0)),
 	// 	op:     _GC_PTR,
@@ -1848,7 +1844,6 @@ func SliceOf(t Type) Type {
 	slice.elem = typ
 	slice.uncommonType = nil
 	slice.ptrToThis = nil
-	slice.zero = unsafe.Pointer(&make([]byte, slice.size)[0])
 
 	if typ.size == 0 {
 		slice.gc = unsafe.Pointer(&sliceEmptyGCProg)
@@ -1920,7 +1915,6 @@ func arrayOf(count int, elem Type) Type {
 	// TODO:
 	array.uncommonType = nil
 	array.ptrToThis = nil
-	array.zero = unsafe.Pointer(&make([]byte, array.size)[0])
 	array.len = uintptr(count)
 	array.slice = slice.(*rtype)
 
diff --git a/libgo/runtime/go-type.h b/libgo/runtime/go-type.h
index 72c9f56986e..eb063ec6789 100644
--- a/libgo/runtime/go-type.h
+++ b/libgo/runtime/go-type.h
@@ -108,11 +108,6 @@ struct __go_type_descriptor
   /* The descriptor for the type which is a pointer to this type.
      This may be NULL.  */
   const struct __go_type_descriptor *__pointer_to_this;
-
-  /* A pointer to a zero value for this type.  All types will point to
-     the same zero value, go$zerovalue, which is a common variable so
-     that it will be large enough.  */
-  void *__zero;
 };
 
 /* The information we store for each method of a type.  */
diff --git a/libgo/runtime/go-unsafe-pointer.c b/libgo/runtime/go-unsafe-pointer.c
index a59ae852185..ce82fcd4070 100644
--- a/libgo/runtime/go-unsafe-pointer.c
+++ b/libgo/runtime/go-unsafe-pointer.c
@@ -10,9 +10,6 @@
 #include "go-type.h"
 #include "mgc0.h"
 
-/* A pointer with a zero value.  */
-static void *zero_pointer;
-
 /* This file provides the type descriptor for the unsafe.Pointer type.
    The unsafe package is defined by the compiler itself, which means
    that there is no package to compile to define the type
@@ -64,9 +61,7 @@ const struct __go_type_descriptor unsafe_Pointer =
   /* __uncommon */
   NULL,
   /* __pointer_to_this */
-  NULL,
-  /* __zero */
-  &zero_pointer
+  NULL
 };
 
 /* We also need the type descriptor for the pointer to unsafe.Pointer,
@@ -109,9 +104,7 @@ const struct __go_ptr_type pointer_unsafe_Pointer =
     /* __uncommon */
     NULL,
     /* __pointer_to_this */
-    NULL,
-    /* __zero */
-    &zero_pointer
+    NULL
   },
   /* __element_type */
   &unsafe_Pointer
diff --git a/libgo/runtime/proc.c b/libgo/runtime/proc.c
index db8b94f28f7..8f82f5b9cc4 100644
--- a/libgo/runtime/proc.c
+++ b/libgo/runtime/proc.c
@@ -538,9 +538,7 @@ static struct __go_channel_type chan_bool_type_descriptor =
       /* __uncommon */
       NULL,
       /* __pointer_to_this */
-      NULL,
-      /* __zero */
-      NULL /* This value doesn't matter */
+      NULL
     },
     /* __element_type */
     &bool_type_descriptor,