From fef26071240711e8f7305715b5f22cfc7ad04bfe Mon Sep 17 00:00:00 2001
From: Mark de Wever <koraq@xs4all.nl>
Date: Sun, 16 Aug 2020 18:40:08 +0200
Subject: [PATCH] [Sema] Use the proper cast for a fixed bool enum.

When casting an enumerate with a fixed bool type the casting should use
an IntegralToBoolean instead of an IntegralCast as is required per Core
Issue 2338.

Fixes PR47055: Incorrect codegen for enum with bool underlying type

Differential Revision: https://reviews.llvm.org/D85612
---
 clang/lib/Sema/SemaCast.cpp      |  8 ++++++-
 clang/test/CXX/drs/dr23xx.cpp    | 13 +++++++++++
 clang/test/CodeGen/enum-bool.cpp | 49 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 69 insertions(+), 1 deletion(-)
 create mode 100644 clang/test/CodeGen/enum-bool.cpp

diff --git a/clang/lib/Sema/SemaCast.cpp b/clang/lib/Sema/SemaCast.cpp
index 9375276..726900c 100644
--- a/clang/lib/Sema/SemaCast.cpp
+++ b/clang/lib/Sema/SemaCast.cpp
@@ -1243,7 +1243,13 @@ static TryCastResult TryStaticCast(Sema &Self, ExprResult &SrcExpr,
       return TC_Failed;
     }
     if (SrcType->isIntegralOrEnumerationType()) {
-      Kind = CK_IntegralCast;
+      // [expr.static.cast]p10 If the enumeration type has a fixed underlying
+      // type, the value is first converted to that type by integral conversion
+      const EnumType *Enum = DestType->getAs<EnumType>();
+      Kind = Enum->getDecl()->isFixed() &&
+                     Enum->getDecl()->getIntegerType()->isBooleanType()
+                 ? CK_IntegralToBoolean
+                 : CK_IntegralCast;
       return TC_Success;
     } else if (SrcType->isRealFloatingType())   {
       Kind = CK_FloatingToIntegral;
diff --git a/clang/test/CXX/drs/dr23xx.cpp b/clang/test/CXX/drs/dr23xx.cpp
index c265ebb..a7ff2a5 100644
--- a/clang/test/CXX/drs/dr23xx.cpp
+++ b/clang/test/CXX/drs/dr23xx.cpp
@@ -4,6 +4,19 @@
 // RUN: %clang_cc1 -std=c++17 %s -verify -fexceptions -fcxx-exceptions -pedantic-errors 2>&1 | FileCheck %s
 // RUN: %clang_cc1 -std=c++2a %s -verify -fexceptions -fcxx-exceptions -pedantic-errors 2>&1 | FileCheck %s
 
+#if __cplusplus >= 201103L
+namespace dr2338 { // dr2338: 12
+namespace B {
+enum E : bool { Zero, One };
+static_assert((int)(E)2 == 1, "");
+} // namespace B
+namespace D {
+enum class E : bool { Zero, One };
+static_assert((int)(E)2 == 1, "");
+} // namespace D
+} // namespace dr2338
+#endif
+
 namespace dr2346 { // dr2346: 11
   void test() {
     const int i2 = 0;
diff --git a/clang/test/CodeGen/enum-bool.cpp b/clang/test/CodeGen/enum-bool.cpp
new file mode 100644
index 0000000..220baa3
--- /dev/null
+++ b/clang/test/CodeGen/enum-bool.cpp
@@ -0,0 +1,49 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown -S -emit-llvm -o - %s | FileCheck %s
+
+namespace dr2338 {
+namespace A {
+enum E { Zero, One };
+E a(int x) { return static_cast<E>(x); }
+// CHECK-LABEL: define i32 @_ZN6dr23381A1aEi
+// CHECK: ret i32 %0
+
+E b(int x) { return (E)x; }
+// CHECK-LABEL: define i32 @_ZN6dr23381A1bEi
+// CHECK: ret i32 %0
+
+} // namespace A
+namespace B {
+enum E : bool { Zero, One };
+E a(int x) { return static_cast<E>(x); }
+// CHECK-LABEL: define zeroext i1 @_ZN6dr23381B1aEi
+// CHECK: ret i1 %tobool
+
+E b(int x) { return (E)x; }
+// CHECK-LABEL: define zeroext i1 @_ZN6dr23381B1bEi
+// CHECK: ret i1 %tobool
+
+} // namespace B
+namespace C {
+enum class E { Zero, One };
+E a(int x) { return static_cast<E>(x); }
+// CHECK-LABEL: define i32 @_ZN6dr23381C1aEi
+// CHECK: ret i32 %0
+
+E b(int x) { return (E)x; }
+// CHECK-LABEL: define i32 @_ZN6dr23381C1bEi
+// CHECK: ret i32 %0
+
+} // namespace C
+namespace D {
+enum class E : bool { Zero, One };
+E a(int x) { return static_cast<E>(x); }
+// CHECK-LABEL: define zeroext i1 @_ZN6dr23381D1aEi
+// CHECK: ret i1 %tobool
+
+E b(int x) { return (E)x; }
+
+// CHECK-LABEL: define zeroext i1 @_ZN6dr23381D1bEi
+// CHECK: ret i1 %tobool
+
+} // namespace D
+} // namespace dr2338
-- 
2.7.4