Allow structs with no members.

Issue #289.

parse.yy

@@ -909,11 +909,21 @@ struct_or_union_specifier
       }
     | struct_or_union '{' '}' 
       {
-          Error(@1, "Empty struct definitions not allowed."); 
+          llvm::SmallVector<const Type *, 8> elementTypes;
+          llvm::SmallVector<std::string, 8> elementNames;
+          llvm::SmallVector<SourcePos, 8> elementPositions;
+          $$ = new StructType("", elementTypes, elementNames, elementPositions,
+                              false, Variability::Unbound, @1);
       }
     | struct_or_union struct_or_union_name '{' '}' 
       {
-          Error(@1, "Empty struct definitions not allowed."); 
+          llvm::SmallVector<const Type *, 8> elementTypes;
+          llvm::SmallVector<std::string, 8> elementNames;
+          llvm::SmallVector<SourcePos, 8> elementPositions;
+          StructType *st = new StructType($2, elementTypes, elementNames, elementPositions,
+                                          false, Variability::Unbound, @1);
+          m->symbolTable->AddType($2, st, @2);
+          $$ = st;
       }
     | struct_or_union struct_or_union_name
       { 

tests/empty-struct.ispc

@@ -0,0 +1,13 @@
+
+export uniform int width() { return programCount; }
+
+struct Foo { };
+
+export void f_f(uniform float RET[], uniform float aFOO[]) {
+    uniform Foo f;
+    RET[programIndex] = sizeof(f); 
+}
+
+export void result(uniform float RET[]) {
+    RET[programIndex] = 1;
+}

type.cpp

@@ -1828,19 +1828,25 @@ StructType::StructType(const std::string &n, const llvm::SmallVector<const Type
 
         // Actually make the LLVM struct
         std::vector<llvm::Type *> elementTypes;
-        for (int i = 0; i < GetElementCount(); ++i) {
+        int nElements = GetElementCount();
-            const Type *type = GetElementType(i);
+        if (nElements == 0) {
-            if (type == NULL) {
+            elementTypes.push_back(LLVMTypes::Int8Type);
-                Assert(m->errorCount > 0);
+        }
-                return;
+        else {
+            for (int i = 0; i < nElements; ++i) {
+                const Type *type = GetElementType(i);
+                if (type == NULL) {
+                    Assert(m->errorCount > 0);
+                    return;
+                }
+                else if (CastType<FunctionType>(type) != NULL) {
+                    Error(elementPositions[i], "Method declarations are not "
+                          "supported.");
+                    return;
+                }
+                else
+                    elementTypes.push_back(type->LLVMType(g->ctx));
             }
-            else if (CastType<FunctionType>(type) != NULL) {
-                Error(elementPositions[i], "Method declarations are not "
-                      "supported.");
-                return;
-            }
-            else
-                elementTypes.push_back(type->LLVMType(g->ctx));
         }
 
         if (lStructTypeMap.find(mname) == lStructTypeMap.end()) {