From 26ea20d88fb1b201546e29058ac4aa5d4760a577 Mon Sep 17 00:00:00 2001
From: Andrew Kelley <superjoe30@gmail.com>
Date: Sun, 7 Feb 2016 15:11:20 -0700
Subject: [PATCH] implement @const_eval

closes #73
---
 src/all_types.hpp    |  1 +
 src/analyze.cpp      | 20 +++++++++++++++++++-
 src/codegen.cpp      |  2 ++
 test/run_tests.cpp   |  7 +++++++
 test/self_hosted.zig |  7 +++++++
 5 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/src/all_types.hpp b/src/all_types.hpp
index 7378e4d6e4..e7e925f42f 100644
--- a/src/all_types.hpp
+++ b/src/all_types.hpp
@@ -1033,6 +1033,7 @@ enum BuiltinFnId {
     BuiltinFnIdCDefine,
     BuiltinFnIdCUndef,
     BuiltinFnIdCompileVar,
+    BuiltinFnIdConstEval,
 };
 
 struct BuiltinFnEntry {
diff --git a/src/analyze.cpp b/src/analyze.cpp
index d6485d0312..2b8119ed48 100644
--- a/src/analyze.cpp
+++ b/src/analyze.cpp
@@ -4127,8 +4127,26 @@ static TypeTableEntry *analyze_builtin_fn_call_expr(CodeGen *g, ImportTableEntry
                         buf_sprintf("unrecognized compile variable: '%s'", buf_ptr(&var_name)));
                     return g->builtin_types.entry_invalid;
                 }
+            }
+        case BuiltinFnIdConstEval:
+            {
+                AstNode **expr_node = node->data.fn_call_expr.params.at(0)->parent_field;
+                TypeTableEntry *resolved_type = analyze_expression(g, import, context, expected_type, *expr_node);
+                if (resolved_type->id == TypeTableEntryIdInvalid) {
+                    return resolved_type;
+                }
 
-                break;
+                ConstExprValue *const_expr_val = &get_resolved_expr(*expr_node)->const_val;
+
+                if (!const_expr_val->ok) {
+                    add_node_error(g, *expr_node, buf_sprintf("unable to evaluate constant expression"));
+                    return resolved_type;
+                }
+
+                ConstExprValue *const_val = &get_resolved_expr(node)->const_val;
+                *const_val = *const_expr_val;
+
+                return resolved_type;
             }
 
     }
diff --git a/src/codegen.cpp b/src/codegen.cpp
index 6ef2a92158..43e78ce194 100644
--- a/src/codegen.cpp
+++ b/src/codegen.cpp
@@ -310,6 +310,7 @@ static LLVMValueRef gen_builtin_fn_call_expr(CodeGen *g, AstNode *node) {
         case BuiltinFnIdMaxValue:
         case BuiltinFnIdMemberCount:
         case BuiltinFnIdCompileVar:
+        case BuiltinFnIdConstEval:
             // caught by constant expression eval codegen
             zig_unreachable();
     }
@@ -3513,6 +3514,7 @@ static void define_builtin_fns(CodeGen *g) {
     create_builtin_fn_with_arg_count(g, BuiltinFnIdCDefine, "c_define", 2);
     create_builtin_fn_with_arg_count(g, BuiltinFnIdCUndef, "c_undef", 1);
     create_builtin_fn_with_arg_count(g, BuiltinFnIdCompileVar, "compile_var", 1);
+    create_builtin_fn_with_arg_count(g, BuiltinFnIdConstEval, "const_eval", 1);
 }
 
 
diff --git a/test/run_tests.cpp b/test/run_tests.cpp
index 4d9de75bfa..318ba36f94 100644
--- a/test/run_tests.cpp
+++ b/test/run_tests.cpp
@@ -2020,6 +2020,13 @@ fn func() -> bogus {}
     add_compile_fail_case("bogus compile var", R"SOURCE(
 const x = @compile_var("bogus");
     )SOURCE", 1, ".tmp_source.zig:2:24: error: unrecognized compile variable: 'bogus'");
+
+
+    add_compile_fail_case("@const_eval", R"SOURCE(
+fn a(x: i32) {
+    const y = @const_eval(x);
+}
+    )SOURCE", 1, ".tmp_source.zig:3:27: error: unable to evaluate constant expression");
 }
 
 //////////////////////////////////////////////////////////////////////////////
diff --git a/test/self_hosted.zig b/test/self_hosted.zig
index 86beb173b0..2ea44adaaa 100644
--- a/test/self_hosted.zig
+++ b/test/self_hosted.zig
@@ -233,3 +233,10 @@ fn const_expr_eval_on_single_expr_blocks_fn(x: i32, b: bool) -> i32 {
 
     return result;
 }
+
+
+#attribute("test")
+fn builtin_const_eval() {
+    const x : i32 = @const_eval(1 + 2 + 3);
+    if (x != @const_eval(6)) unreachable{};
+}