Allow unions with one variant to be constant

4 files changed, 82 insertions, 4 deletions

diff --git a/src/check_decl.cpp b/src/check_decl.cpp
index 092222d3c..bda1059fb 100644
--- a/src/check_decl.cpp
+++ b/src/check_decl.cpp
@@ -1565,7 +1565,7 @@ gb_internal void check_proc_decl(CheckerContext *ctx, Entity *e, DeclInfo *d) {
 	}
 }
 
-gb_internal void check_global_variable_decl(CheckerContext *ctx, Entity *&e, Ast *type_expr, Ast *init_expr) {
+gb_internal void check_global_variable_decl(CheckerContext *ctx, Entity *e, Ast *type_expr, Ast *init_expr) {
 	GB_ASSERT(e->type == nullptr);
 	GB_ASSERT(e->kind == Entity_Variable);
 
diff --git a/src/check_expr.cpp b/src/check_expr.cpp
index d863d6cf6..0ea0952f9 100644
--- a/src/check_expr.cpp
+++ b/src/check_expr.cpp
@@ -3500,6 +3500,21 @@ gb_internal bool check_is_castable_to(CheckerContext *c, Operand *operand, Type
 	return false;
 }
 
+gb_internal bool is_type_union_constantable(Type *type) {
+	Type *bt = base_type(type);
+	GB_ASSERT(bt->kind == Type_Union);
+
+
+	if (bt->Union.variants.count <= 1) {
+		return true;
+	}
+
+	// for (Type *v : bt->Union.variants) {
+
+	// }
+	return false;
+}
+
 gb_internal bool check_cast_internal(CheckerContext *c, Operand *x, Type *type) {
 	bool is_const_expr = x->mode == Addressing_Constant;
 
@@ -3524,6 +3539,9 @@ gb_internal bool check_cast_internal(CheckerContext *c, Operand *x, Type *type)
 		} else if (is_type_slice(type) && is_type_string(x->type)) {
 			x->mode = Addressing_Value;
 		} else if (is_type_union(type)) {
+			if (is_type_union_constantable(type)) {
+				return true;
+			}
 			x->mode = Addressing_Value;
 		}
 		if (x->mode == Addressing_Value) {
@@ -3582,7 +3600,11 @@ gb_internal void check_cast(CheckerContext *c, Operand *x, Type *type, bool forb
 		Type *final_type = type;
 		if (is_const_expr && !is_type_constant_type(type)) {
 			if (is_type_union(type)) {
-				convert_to_typed(c, x, type);
+				if (is_type_union_constantable(type)) {
+
+				} else {
+					convert_to_typed(c, x, type);
+				}
 			}
 			final_type = default_type(x->type);
 		}
@@ -8151,7 +8173,11 @@ gb_internal ExprKind check_call_expr(CheckerContext *c, Operand *operand, Ast *c
 					} else {
 						// NOTE(bill): Otherwise the compiler can override the polymorphic type
 						// as it assumes it is determining the type
+						AddressingMode old_mode = operand->mode;
 						check_cast(c, operand, t);
+						if (old_mode == Addressing_Constant && old_mode != operand->mode) {
+							gb_printf_err("HERE: %d -> %d %s\n", old_mode, operand->mode, expr_to_string(operand->expr));
+						}
 					}
 				}
 				operand->type = t;
diff --git a/src/llvm_backend_const.cpp b/src/llvm_backend_const.cpp
index e64be49f2..98e50dd78 100644
--- a/src/llvm_backend_const.cpp
+++ b/src/llvm_backend_const.cpp
@@ -168,7 +168,7 @@ gb_internal LLVMValueRef llvm_const_named_struct(lbModule *m, Type *t, LLVMValue
 		return llvm_const_named_struct_internal(struct_type, values, value_count_);
 	}
 	Type *bt = base_type(t);
-	GB_ASSERT(bt->kind == Type_Struct);
+	GB_ASSERT(bt->kind == Type_Struct || bt->kind == Type_Union);
 	
 	GB_ASSERT(value_count_ == bt->Struct.fields.count);
 	
@@ -585,6 +585,47 @@ gb_internal lbValue lb_const_value(lbModule *m, Type *type, ExactValue value, lb
 
 	bool is_local = cc.allow_local && m->curr_procedure != nullptr;
 
+	if (is_type_union(type) && is_type_union_constantable(type)) {
+		Type *bt = base_type(type);
+		GB_ASSERT(bt->kind == Type_Union);
+		GB_ASSERT(bt->Union.variants.count <= 1);
+		if (bt->Union.variants.count == 0) {
+			return lb_const_nil(m, original_type);
+		} else if (bt->Union.variants.count == 1) {
+			Type *t = bt->Union.variants[0];
+			lbValue cv =  lb_const_value(m, t, value, cc);
+			GB_ASSERT(LLVMIsConstant(cv.value));
+
+			LLVMTypeRef llvm_type = lb_type(m, original_type);
+
+			if (is_type_union_maybe_pointer(type)) {
+				LLVMValueRef values[1] = {cv.value};
+				res.value = llvm_const_named_struct_internal(llvm_type, values, 1);
+				res.type = original_type;
+				return res;
+			} else {
+
+				unsigned tag_value = 1;
+				if (bt->Union.kind == UnionType_no_nil) {
+					tag_value = 0;
+				}
+				LLVMValueRef tag = LLVMConstInt(LLVMStructGetTypeAtIndex(llvm_type, 1), tag_value, false);
+				LLVMValueRef padding = nullptr;
+				LLVMValueRef values[3] = {cv.value, tag, padding};
+
+				isize value_count = 2;
+				if (LLVMCountStructElementTypes(llvm_type) > 2) {
+					value_count = 3;
+					padding = LLVMConstNull(LLVMStructGetTypeAtIndex(llvm_type, 2));
+				}
+				res.value = llvm_const_named_struct_internal(llvm_type, values, value_count);
+				res.type = original_type;
+				return res;
+			}
+		}
+
+	}
+
 	// GB_ASSERT_MSG(is_type_typed(type), "%s", type_to_string(type));
 
 	if (is_type_slice(type)) {
diff --git a/src/llvm_backend_general.cpp b/src/llvm_backend_general.cpp
index 57eb869fa..cae08ec2f 100644
--- a/src/llvm_backend_general.cpp
+++ b/src/llvm_backend_general.cpp
@@ -2226,6 +2226,18 @@ gb_internal LLVMTypeRef lb_type_internal(lbModule *m, Type *type) {
 			if (is_type_union_maybe_pointer(type)) {
 				LLVMTypeRef variant = lb_type(m, type->Union.variants[0]);
 				array_add(&fields, variant);
+			} else if (type->Union.variants.count == 1) {
+				LLVMTypeRef block_type = lb_type(m, type->Union.variants[0]);
+
+				LLVMTypeRef tag_type = lb_type(m, union_tag_type(type));
+				array_add(&fields, block_type);
+				array_add(&fields, tag_type);
+				i64 used_size = lb_sizeof(block_type) + lb_sizeof(tag_type);
+				i64 padding = size - used_size;
+				if (padding > 0) {
+					LLVMTypeRef padding_type = lb_type_padding_filler(m, padding, align);
+					array_add(&fields, padding_type);
+				}
 			} else {
 				LLVMTypeRef block_type = nullptr;
 
@@ -3131,7 +3143,6 @@ gb_internal lbValue lb_generate_anonymous_proc_lit(lbModule *m, String const &pr
 		lbValue *found = map_get(&target_module->values, e);
 		rw_mutex_shared_unlock(&target_module->values_mutex);
 		if (found == nullptr) {
-			// THIS IS THE RACE CONDITION
 			lbProcedure *missing_proc_in_target_module = lb_create_procedure(target_module, e, false);
 			array_add(&target_module->missing_procedures_to_check, missing_proc_in_target_module);
 		}