r280838 - Try contextually converting condition of constexpr if to Boolean value
Ismail Pazarbasi via cfe-commits
cfe-commits at lists.llvm.org
Wed Sep 7 11:24:54 PDT 2016
Author: ismailp
Date: Wed Sep 7 13:24:54 2016
New Revision: 280838
URL: http://llvm.org/viewvc/llvm-project?rev=280838&view=rev
Log:
Try contextually converting condition of constexpr if to Boolean value
Summary:
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.
Reviewers: rsmith
Subscribers: cfe-commits
Differential Revision: https://reviews.llvm.org/D24158
Modified:
cfe/trunk/lib/Sema/SemaOverload.cpp
cfe/trunk/test/CXX/stmt.stmt/stmt.select/stmt.if/p2.cpp
cfe/trunk/test/CodeGenCXX/cxx1z-constexpr-if.cpp
Modified: cfe/trunk/lib/Sema/SemaOverload.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaOverload.cpp?rev=280838&r1=280837&r2=280838&view=diff
==============================================================================
--- cfe/trunk/lib/Sema/SemaOverload.cpp (original)
+++ cfe/trunk/lib/Sema/SemaOverload.cpp Wed Sep 7 13:24:54 2016
@@ -5164,12 +5164,18 @@ static ExprResult CheckConvertedConstant
// 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:
Modified: cfe/trunk/test/CXX/stmt.stmt/stmt.select/stmt.if/p2.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CXX/stmt.stmt/stmt.select/stmt.if/p2.cpp?rev=280838&r1=280837&r2=280838&view=diff
==============================================================================
--- cfe/trunk/test/CXX/stmt.stmt/stmt.select/stmt.if/p2.cpp (original)
+++ cfe/trunk/test/CXX/stmt.stmt/stmt.select/stmt.if/p2.cpp Wed Sep 7 13:24:54 2016
@@ -46,6 +46,11 @@ namespace ccce {
if constexpr (N) {} // expected-error {{cannot be narrowed}}
}
template void g<5>(); // expected-note {{instantiation of}}
+ void h() {
+ if constexpr (4.3) {} // expected-error{{conversion from 'double' to 'bool' is not allowed in a converted constant expression}}
+ constexpr void *p = nullptr;
+ if constexpr (p) {} // expected-error{{conversion from 'void *const' to 'bool' is not allowed in a converted constant expression}}
+ }
}
namespace generic_lambda {
Modified: cfe/trunk/test/CodeGenCXX/cxx1z-constexpr-if.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGenCXX/cxx1z-constexpr-if.cpp?rev=280838&r1=280837&r2=280838&view=diff
==============================================================================
--- cfe/trunk/test/CodeGenCXX/cxx1z-constexpr-if.cpp (original)
+++ cfe/trunk/test/CodeGenCXX/cxx1z-constexpr-if.cpp Wed Sep 7 13:24:54 2016
@@ -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 @@ void f() {
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
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