From a05150e92d5925f14591d96220de3bb341be1154 Mon Sep 17 00:00:00 2001
From: Andrew Kelley <andrew@ziglang.org>
Date: Mon, 30 Dec 2019 19:08:57 -0500
Subject: [PATCH] fix comparing comptime_int against undefined literal

closes #4004
---
 src/analyze.cpp               | 2 +-
 src/ir.cpp                    | 4 +++-
 test/compile_errors.zig       | 8 ++++++++
 test/stage1/behavior/math.zig | 7 +++++++
 4 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/src/analyze.cpp b/src/analyze.cpp
index dacb1d2b70f0219e2c8d75fb71eb4bdad8128fd6..8be25b759251c41ec0d33c63b63df270564d14b4 100644
--- a/src/analyze.cpp
+++ b/src/analyze.cpp
@@ -9243,6 +9243,7 @@ bool type_is_numeric(ZigType *ty) {
         case ZigTypeIdComptimeInt:
         case ZigTypeIdInt:
         case ZigTypeIdFloat:
+        case ZigTypeIdUndefined:
             return true;
 
         case ZigTypeIdVector:
@@ -9255,7 +9256,6 @@ bool type_is_numeric(ZigType *ty) {
         case ZigTypeIdPointer:
         case ZigTypeIdArray:
         case ZigTypeIdStruct:
-        case ZigTypeIdUndefined:
         case ZigTypeIdNull:
         case ZigTypeIdOptional:
         case ZigTypeIdErrorUnion:
diff --git a/src/ir.cpp b/src/ir.cpp
index 149c41dfec222f6628c3ff40458ad285a187eea5..bf5a297a811c05aab40e89ff62e012a99263ef4d 100644
--- a/src/ir.cpp
+++ b/src/ir.cpp
@@ -14647,7 +14647,9 @@ never_mind_just_calculate_it_normally:
     }
 
 
-    if (op1_val->special == ConstValSpecialUndef || op2_val->special == ConstValSpecialUndef) {
+    if (op1_val->special == ConstValSpecialUndef || op2_val->special == ConstValSpecialUndef ||
+        op1_val->type->id == ZigTypeIdUndefined || op2_val->type->id == ZigTypeIdUndefined)
+    {
         out_val->special = ConstValSpecialUndef;
         return nullptr;
     }
diff --git a/test/compile_errors.zig b/test/compile_errors.zig
index a653e1662ec3af7094d92faa27b7e9d32cd6d9f2..1c09ed9edf87697565b1b04b0e1a64caba428819 100644
--- a/test/compile_errors.zig
+++ b/test/compile_errors.zig
@@ -2,6 +2,14 @@ const tests = @import("tests.zig");
 const builtin = @import("builtin");
 
 pub fn addCases(cases: *tests.CompileErrorContext) void {
+    cases.add("comparing against undefined produces undefined value",
+        \\export fn entry() void {
+        \\    if (2 == undefined) {}
+        \\}
+    , &[_][]const u8{
+        "tmp.zig:2:11: error: use of undefined value here causes undefined behavior",
+    });
+
     cases.add("comptime ptrcast of zero-sized type",
         \\fn foo() void {
         \\    const node: struct {} = undefined;
diff --git a/test/stage1/behavior/math.zig b/test/stage1/behavior/math.zig
index 3a73e776eb1cf35578fcf36c9d809efc73b835be..90260d4e021a439837b95ecf21f1b78044a2cacf 100644
--- a/test/stage1/behavior/math.zig
+++ b/test/stage1/behavior/math.zig
@@ -671,3 +671,10 @@ test "vector comparison" {
     S.doTheTest();
     comptime S.doTheTest();
 }
+
+test "compare undefined literal with comptime_int" {
+    var x = undefined == 1;
+    // x is now undefined with type bool
+    x = true;
+    expect(x);
+}
-- 
2.54.0