Add experimental @noalias attribute.

releasenotes.md

@@ -20,6 +20,7 @@
 - `$expand` macro, to expand a string into code.
 - && doesn't work correctly with lambdas #1279.
 - Fix incorrect override of optimization levels when using projects.
+- Add experimental `@noalias` attribute.
 
 ### Fixes
 

src/compiler/compiler_internal.h

@@ -472,6 +472,7 @@ typedef struct VarDecl_
 	bool is_addr : 1;
 	bool is_threadlocal : 1;
 	bool no_init : 1;
+	bool no_alias : 1;
 	bool bit_is_expr : 1;
 	TypeInfoId type_info;
 	union

src/compiler/enums.h

@@ -824,6 +824,7 @@ typedef enum
 	ATTRIBUTE_LOCAL,
 	ATTRIBUTE_MAYDISCARD,
 	ATTRIBUTE_NAKED,
+	ATTRIBUTE_NOALIAS,
 	ATTRIBUTE_NODISCARD,
 	ATTRIBUTE_NOINIT,
 	ATTRIBUTE_NOINLINE,

src/compiler/llvm_codegen.c

@@ -1069,7 +1069,8 @@ LLVMValueRef llvm_get_opt_ref(GenContext *c, Decl *decl)
 	return decl->var.optional_ref;
 }
 
-static void llvm_emit_param_attributes(GenContext *c, LLVMValueRef function, ABIArgInfo *info, bool is_return, int index, int last_index)
+static void llvm_emit_param_attributes(GenContext *c, LLVMValueRef function, ABIArgInfo *info, bool is_return,
+                                       int index, int last_index, Decl *decl)
 {
 	assert(last_index == index || info->kind == ABI_ARG_DIRECT_PAIR || info->kind == ABI_ARG_IGNORE
 		   || info->kind == ABI_ARG_EXPAND || info->kind == ABI_ARG_DIRECT || info->kind == ABI_ARG_DIRECT_COERCE
@@ -1094,13 +1095,18 @@ static void llvm_emit_param_attributes(GenContext *c, LLVMValueRef function, ABI
 	}
 	switch (info->kind)
 	{
+		case ABI_ARG_DIRECT:
+			if (decl && decl->var.no_alias)
+			{
+				llvm_attribute_add(c, function, attribute_id.noalias, 1);
+			}
+			break;
 		case ABI_ARG_EXPAND:
 		case ABI_ARG_IGNORE:
 		case ABI_ARG_DIRECT_SPLIT_STRUCT_I32:
 		case ABI_ARG_DIRECT_COERCE:
 		case ABI_ARG_DIRECT_COERCE_INT:
 		case ABI_ARG_DIRECT_PAIR:
-		case ABI_ARG_DIRECT:
 		case ABI_ARG_EXPAND_COERCE:
 			break;
 		case ABI_ARG_INDIRECT:
@@ -1127,7 +1133,7 @@ void llvm_append_function_attributes(GenContext *c, Decl *decl)
 
 	LLVMValueRef function = decl->backend_ref;
 	ABIArgInfo *ret_abi_info = prototype->ret_abi_info;
-	llvm_emit_param_attributes(c, function, ret_abi_info, true, 0, 0);
+	llvm_emit_param_attributes(c, function, ret_abi_info, true, 0, 0, NULL);
 	unsigned params = vec_size(prototype->param_types);
 	if (c->debug.enable_stacktrace)
 	{
@@ -1140,12 +1146,13 @@ void llvm_append_function_attributes(GenContext *c, Decl *decl)
 	if (prototype->ret_by_ref)
 	{
 		ABIArgInfo *info = prototype->ret_by_ref_abi_info;
-		llvm_emit_param_attributes(c, function, prototype->ret_by_ref_abi_info, false, info->param_index_start + 1, info->param_index_end);
+		llvm_emit_param_attributes(c, function, prototype->ret_by_ref_abi_info, false, info->param_index_start + 1,
+		                           info->param_index_end, NULL);
 	}
 	for (unsigned i = 0; i < params; i++)
 	{
 		ABIArgInfo *info = prototype->abi_args[i];
-		llvm_emit_param_attributes(c, function, info, false, info->param_index_start + 1, info->param_index_end);
+		llvm_emit_param_attributes(c, function, info, false, info->param_index_start + 1, info->param_index_end, decl->func_decl.signature.params[i]);
 	}
 	// We ignore decl->func_decl.attr_inline and place it in every call instead.
 	if (decl->func_decl.attr_noinline)

src/compiler/sema_decls.c

@@ -1200,12 +1200,17 @@ static inline bool sema_analyse_signature(SemaContext *context, Signature *sig,
 			                                     : RESOLVE_TYPE_DEFAULT)) return decl_poison(param);
 			param->type = type_info->type;
 		}
+		if (type_info && param->var.no_alias && !type_is_pointer(param->type) && type_flatten(param->type)->type_kind != TYPE_SLICE)
+		{
+			SEMA_ERROR(param, "The parameter was set to @noalias, but it was neither a slice nor a pointer. You need to either remove '@noalias' or use pointer/slice type.");
+			return decl_poison(param);
+		}
 		switch (var_kind)
 		{
 			case VARDECL_PARAM_REF:
 				if (type_info && !type_is_pointer(param->type))
 				{
-					RETURN_SEMA_ERROR(type_info, "A pointer type was expected for a ref argument, did you mean %s?",
+					SEMA_ERROR(type_info, "A pointer type was expected for a ref argument, did you mean %s?",
 							   type_quoted_error_string(type_get_ptr(param->type)));
 					return decl_poison(param);
 				}
@@ -2359,6 +2364,7 @@ static bool sema_analyse_attribute(SemaContext *context, Decl *decl, Attr *attr,
 			[ATTRIBUTE_LOCAL] = ATTR_FUNC | ATTR_MACRO | ATTR_GLOBAL | ATTR_CONST | USER_DEFINED_TYPES | ATTR_DEF | ATTR_INTERFACE,
 			[ATTRIBUTE_MAYDISCARD] = CALLABLE_TYPE,
 			[ATTRIBUTE_NAKED] = ATTR_FUNC,
+			[ATTRIBUTE_NOALIAS] = ATTR_PARAM,
 			[ATTRIBUTE_NODISCARD] = CALLABLE_TYPE,
 			[ATTRIBUTE_NOINIT] = ATTR_GLOBAL | ATTR_LOCAL,
 			[ATTRIBUTE_NOINLINE] = ATTR_FUNC | ATTR_CALL,
@@ -2519,6 +2525,9 @@ static bool sema_analyse_attribute(SemaContext *context, Decl *decl, Attr *attr,
 		case ATTRIBUTE_NOSTRIP:
 			decl->no_strip = true;
 			return true;
+		case ATTRIBUTE_NOALIAS:
+			decl->var.no_alias = true;
+			return true;
 		case ATTRIBUTE_IF:
 			if (!expr) RETURN_SEMA_ERROR(attr, "'@if' requires a boolean argument.");
 			if (!sema_analyse_expr(context, expr)) return false;

src/compiler/symtab.c

@@ -326,6 +326,7 @@ void symtab_init(uint32_t capacity)
 	attribute_list[ATTRIBUTE_LOCAL] = KW_DEF("@local");
 	attribute_list[ATTRIBUTE_MAYDISCARD] = KW_DEF("@maydiscard");
 	attribute_list[ATTRIBUTE_NAKED] = KW_DEF("@naked");
+	attribute_list[ATTRIBUTE_NOALIAS] = KW_DEF("@noalias");
 	attribute_list[ATTRIBUTE_NODISCARD] = KW_DEF("@nodiscard");
 	attribute_list[ATTRIBUTE_NOINIT] = KW_DEF("@noinit");
 	attribute_list[ATTRIBUTE_NOINLINE] = KW_DEF("@noinline");