bruno created this revision.
bruno added reviewers: rsmith, ahatanak, erik.pilkington.
Herald added subscribers: dexonsmith, jkorous.
Implement support for try-catch blocks in constexpr functions, as
proposed in http://wg21.link/P1002 and voted in San Diego for c++20.
The idea is that we can still never throw inside constexpr, so the catch
block is never entered. A try-catch block like this:
try { f(); } catch (...) { }
is then morally equivalent to just
{ f(); }
Same idea should apply for function/constructor try blocks.
rdar://problem/45530773
https://reviews.llvm.org/D55097
Files:
lib/AST/ExprConstant.cpp
lib/Sema/SemaDeclCXX.cpp
test/CXX/dcl.dcl/dcl.spec/dcl.constexpr/p3.cpp
test/CXX/dcl.dcl/dcl.spec/dcl.constexpr/p4.cpp
test/CXX/drs/dr6xx.cpp
www/cxx_status.html
Index: www/cxx_status.html
===================================================================
--- www/cxx_status.html
+++ www/cxx_status.html
@@ -953,13 +953,15 @@
<tr>
<td rowspan=4>Relaxations of <tt>constexpr</tt> restrictions</td>
<td><a href="http://wg21.link/p1064r0";>P1064R0</a></td>
- <td rowspan=4 class="none" align="center">No</td>
+ <td class="none" align="center">No</td>
</tr>
<tr> <!-- from San Diego -->
<td><a href="http://wg21.link/p1002r1";>P1002R1</a></td>
+ <td class="full" align="center">Clang 8</td>
</tr>
<tr>
<td><a href="http://wg21.link/p1327r1";>P1327R1</a></td>
+ <td rowspan=2 class="none" align="center">No</td>
</tr>
<tr>
<td><a href="http://wg21.link/p1330r0";>P1330R0</a></td>
Index: test/CXX/drs/dr6xx.cpp
===================================================================
--- test/CXX/drs/dr6xx.cpp
+++ test/CXX/drs/dr6xx.cpp
@@ -492,7 +492,10 @@
struct C {
constexpr C(NonLiteral);
constexpr C(NonLiteral, int) {} // expected-error {{not a literal type}}
- constexpr C() try {} catch (...) {} // expected-error {{function try block}}
+ constexpr C() try {} catch (...) {}
+#if __cplusplus <= 201703L
+ // expected-error@-2 {{function try block}}
+#endif
};
struct D {
Index: test/CXX/dcl.dcl/dcl.spec/dcl.constexpr/p4.cpp
===================================================================
--- test/CXX/dcl.dcl/dcl.spec/dcl.constexpr/p4.cpp
+++ test/CXX/dcl.dcl/dcl.spec/dcl.constexpr/p4.cpp
@@ -1,5 +1,6 @@
// RUN: %clang_cc1 -verify -std=c++11 -fcxx-exceptions -Werror=c++1y-extensions %s
// RUN: %clang_cc1 -verify -std=c++1y -fcxx-exceptions -DCXX1Y %s
+// RUN: %clang_cc1 -verify -std=c++2a -fcxx-exceptions -DCXX1Y -DCXX2A %s
namespace N {
typedef char C;
@@ -49,7 +50,10 @@
// - its function-body shall not be a function-try-block;
struct U {
constexpr U()
- try // expected-error {{function try block not allowed in constexpr constructor}}
+ try
+#ifndef CXX2A
+ // expected-error@-2 {{function try block not allowed in constexpr constructor}}
+#endif
: u() {
} catch (...) {
throw;
Index: test/CXX/dcl.dcl/dcl.spec/dcl.constexpr/p3.cpp
===================================================================
--- test/CXX/dcl.dcl/dcl.spec/dcl.constexpr/p3.cpp
+++ test/CXX/dcl.dcl/dcl.spec/dcl.constexpr/p3.cpp
@@ -1,5 +1,6 @@
// RUN: %clang_cc1 -verify -fcxx-exceptions -triple=x86_64-linux-gnu -std=c++11 -Werror=c++1y-extensions %s
// RUN: %clang_cc1 -verify -fcxx-exceptions -triple=x86_64-linux-gnu -std=c++1y -DCXX1Y %s
+// RUN: %clang_cc1 -verify -fcxx-exceptions -triple=x86_64-linux-gnu -std=c++2a -DCXX1Y -DCXX2A %s
namespace N {
typedef char C;
@@ -78,7 +79,12 @@
};
struct T3 {
constexpr T3 &operator=(const T3&) const = default;
- // expected-error@-1 {{an explicitly-defaulted copy assignment operator may not have 'const' or 'volatile' qualifiers}}
+#ifndef CXX2A
+ // expected-error@-2 {{an explicitly-defaulted copy assignment operator may not have 'const' or 'volatile' qualifiers}}
+#else
+ // expected-warning@-4 {{explicitly defaulted copy assignment operator is implicitly deleted}}
+ // expected-note@-5 {{function is implicitly deleted because its declared type does not match the type of an implicit copy assignment operator}}
+#endif
};
#endif
struct U {
@@ -131,7 +137,10 @@
}
constexpr int DisallowedStmtsCXX1Y_3() {
// - a try-block,
- try {} catch (...) {} // expected-error {{statement not allowed in constexpr function}}
+ try {} catch (...) {}
+#ifndef CXX2A
+ // expected-error@-2 {{statement not allowed in constexpr function}}
+#endif
return 0;
}
constexpr int DisallowedStmtsCXX1Y_4() {
Index: lib/Sema/SemaDeclCXX.cpp
===================================================================
--- lib/Sema/SemaDeclCXX.cpp
+++ lib/Sema/SemaDeclCXX.cpp
@@ -1900,6 +1900,27 @@
return false;
return true;
+ case Stmt::CXXTryStmtClass:
+ if (!SemaRef.getLangOpts().CPlusPlus2a)
+ break;
+ if (!Cxx1yLoc.isValid())
+ Cxx1yLoc = S->getBeginLoc();
+ for (Stmt *SubStmt : S->children())
+ if (SubStmt &&
+ !CheckConstexprFunctionStmt(SemaRef, Dcl, SubStmt, ReturnStmts,
+ Cxx1yLoc))
+ return false;
+ return true;
+
+ case Stmt::CXXCatchStmtClass:
+ if (!SemaRef.getLangOpts().CPlusPlus2a)
+ break;
+ if (!Cxx1yLoc.isValid())
+ Cxx1yLoc = S->getBeginLoc();
+ // In case we got a valid constexpr try block, the catch block can be
+ // ignored since it will never be evaluated in a constexpr context.
+ return true;
+
default:
if (!isa<Expr>(S))
break;
@@ -1920,6 +1941,8 @@
///
/// \return true if the body is OK, false if we have diagnosed a problem.
bool Sema::CheckConstexprFunctionBody(const FunctionDecl *Dcl, Stmt *Body) {
+ SmallVector<SourceLocation, 4> ReturnStmts;
+
if (isa<CXXTryStmt>(Body)) {
// C++11 [dcl.constexpr]p3:
// The definition of a constexpr function shall satisfy the following
@@ -1930,12 +1953,25 @@
// C++11 [dcl.constexpr]p4:
// In the definition of a constexpr constructor, [...]
// - its function-body shall not be a function-try-block;
- Diag(Body->getBeginLoc(), diag::err_constexpr_function_try_block)
- << isa<CXXConstructorDecl>(Dcl);
- return false;
- }
+ if (!getLangOpts().CPlusPlus2a) {
+ Diag(Body->getBeginLoc(), diag::err_constexpr_function_try_block)
+ << isa<CXXConstructorDecl>(Dcl);
+ return false;
+ }
- SmallVector<SourceLocation, 4> ReturnStmts;
+ // constexpr function try blocks are allowed in c++2a, assuming that the
+ // inner statements do also apply to general constexpr rules.
+ SourceLocation Cxx1yLoc;
+ for (Stmt *SubStmt : Body->children())
+ if (SubStmt &&
+ !CheckConstexprFunctionStmt(*this, Dcl, SubStmt, ReturnStmts,
+ Cxx1yLoc))
+ return false;
+ if (Cxx1yLoc.isValid())
+ Diag(Cxx1yLoc, diag::warn_cxx11_compat_constexpr_body_invalid_stmt)
+ << isa<CXXConstructorDecl>(Dcl);
+ return true;
+ }
// - its function-body shall be [...] a compound-statement that contains only
// [... list of cases ...]
Index: lib/AST/ExprConstant.cpp
===================================================================
--- lib/AST/ExprConstant.cpp
+++ lib/AST/ExprConstant.cpp
@@ -4274,6 +4274,23 @@
case Stmt::CaseStmtClass:
case Stmt::DefaultStmtClass:
return EvaluateStmt(Result, Info, cast<SwitchCase>(S)->getSubStmt(), Case);
+ case Stmt::CXXTryStmtClass: {
+ // Evaluate try blocks by evaluating all sub statements and keep track
+ // whether there's a return.
+ EvalStmtResult ESR = ESR_Succeeded;
+ for (const Stmt *SubStmt : S->children()) {
+ EvalStmtResult SubStmtESR = EvaluateStmt(Result, Info, SubStmt, Case);
+ if (SubStmtESR != ESR_Succeeded && SubStmtESR != ESR_Returned)
+ return ESR_Failed;
+ if (SubStmtESR == ESR_Returned)
+ ESR = SubStmtESR;
+ }
+ return ESR;
+ }
+ case Stmt::CXXCatchStmtClass:
+ // No need to evaluate catch since it will be ignored in case the try block
+ // is successfully evaluated.
+ return ESR_Succeeded;
}
}
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