ismailp created this revision.
ismailp added a reviewer: rsmith.
ismailp added a subscriber: cfe-commits.
C++1z 6.4.1/p2:
If the if statement is of the form if constexpr, the value of the
condition shall be a contextually converted constant expression of type
bool [...]
C++1z 5.20/p4:
[...] A contextually converted constant expression of type bool is an
expression, contextually converted to bool (Clause4), where the
converted expression is a constant expression and the conversion
sequence contains only the conversions above. [...]
Contextually converting result of an expression `e` to a Boolean value
requires `bool t(e)` to be well-formed.
An explicit conversion function is only considered as a user-defined
conversion for direct-initialization, which is essentially what
//contextually converted to bool// requires.
Also, fixes PR28470.
https://reviews.llvm.org/D24158
Files:
lib/Sema/SemaOverload.cpp
test/CodeGenCXX/cxx1z-constexpr-if.cpp
Index: test/CodeGenCXX/cxx1z-constexpr-if.cpp
===================================================================
--- test/CodeGenCXX/cxx1z-constexpr-if.cpp
+++ test/CodeGenCXX/cxx1z-constexpr-if.cpp
@@ -2,7 +2,15 @@
void should_be_used_1();
void should_be_used_2();
+void should_be_used_3();
void should_not_be_used();
+
+struct A {
+ constexpr explicit operator bool() const {
+ return true;
+ }
+};
+
void f() {
if constexpr (false)
should_not_be_used();
@@ -15,7 +23,12 @@
goto foo;
foo: should_not_be_used();
}
+ if constexpr (A())
+ should_be_used_3();
+ else
+ should_not_be_used();
}
// CHECK: should_be_used_1
// CHECK: should_be_used_2
+// CHECK: should_be_used_3
Index: lib/Sema/SemaOverload.cpp
===================================================================
--- lib/Sema/SemaOverload.cpp
+++ lib/Sema/SemaOverload.cpp
@@ -5140,12 +5140,18 @@
// implicitly converted to type T, where the converted
// expression is a constant expression and the implicit conversion
// sequence contains only [... list of conversions ...].
+ // C++1z [stmt.if]p2:
+ // If the if statement is of the form if constexpr, the value of the
+ // condition shall be a contextually converted constant expression of type
+ // bool.
ImplicitConversionSequence ICS =
- TryCopyInitialization(S, From, T,
- /*SuppressUserConversions=*/false,
- /*InOverloadResolution=*/false,
- /*AllowObjcWritebackConversion=*/false,
- /*AllowExplicit=*/false);
+ CCE == Sema::CCEK_ConstexprIf
+ ? TryContextuallyConvertToBool(S, From)
+ : TryCopyInitialization(S, From, T,
+ /*SuppressUserConversions=*/false,
+ /*InOverloadResolution=*/false,
+ /*AllowObjcWritebackConversion=*/false,
+ /*AllowExplicit=*/false);
StandardConversionSequence *SCS = nullptr;
switch (ICS.getKind()) {
case ImplicitConversionSequence::StandardConversion:
Index: test/CodeGenCXX/cxx1z-constexpr-if.cpp
===================================================================
--- test/CodeGenCXX/cxx1z-constexpr-if.cpp
+++ test/CodeGenCXX/cxx1z-constexpr-if.cpp
@@ -2,7 +2,15 @@
void should_be_used_1();
void should_be_used_2();
+void should_be_used_3();
void should_not_be_used();
+
+struct A {
+ constexpr explicit operator bool() const {
+ return true;
+ }
+};
+
void f() {
if constexpr (false)
should_not_be_used();
@@ -15,7 +23,12 @@
goto foo;
foo: should_not_be_used();
}
+ if constexpr (A())
+ should_be_used_3();
+ else
+ should_not_be_used();
}
// CHECK: should_be_used_1
// CHECK: should_be_used_2
+// CHECK: should_be_used_3
Index: lib/Sema/SemaOverload.cpp
===================================================================
--- lib/Sema/SemaOverload.cpp
+++ lib/Sema/SemaOverload.cpp
@@ -5140,12 +5140,18 @@
// implicitly converted to type T, where the converted
// expression is a constant expression and the implicit conversion
// sequence contains only [... list of conversions ...].
+ // C++1z [stmt.if]p2:
+ // If the if statement is of the form if constexpr, the value of the
+ // condition shall be a contextually converted constant expression of type
+ // bool.
ImplicitConversionSequence ICS =
- TryCopyInitialization(S, From, T,
- /*SuppressUserConversions=*/false,
- /*InOverloadResolution=*/false,
- /*AllowObjcWritebackConversion=*/false,
- /*AllowExplicit=*/false);
+ CCE == Sema::CCEK_ConstexprIf
+ ? TryContextuallyConvertToBool(S, From)
+ : TryCopyInitialization(S, From, T,
+ /*SuppressUserConversions=*/false,
+ /*InOverloadResolution=*/false,
+ /*AllowObjcWritebackConversion=*/false,
+ /*AllowExplicit=*/false);
StandardConversionSequence *SCS = nullptr;
switch (ICS.getKind()) {
case ImplicitConversionSequence::StandardConversion:
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