shafik created this revision.
shafik added reviewers: aaron.ballman, erichkeane.
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shafik requested review of this revision.
DR2338 <https://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#2338>
clarified that it was undefined behavior to set the value outside the range of
the enumerations values for an enum without a fixed underlying type.
We should diagnose this with a constant expression context. This PR adds this
diagnosis for C++20 since the DR status was CD5 and a test to verify the
behavior.
https://reviews.llvm.org/D130058
Files:
clang/include/clang/Basic/DiagnosticASTKinds.td
clang/lib/AST/ExprConstant.cpp
clang/test/SemaCXX/constant-expression-cxx2a.cpp
Index: clang/test/SemaCXX/constant-expression-cxx2a.cpp
===================================================================
--- clang/test/SemaCXX/constant-expression-cxx2a.cpp
+++ clang/test/SemaCXX/constant-expression-cxx2a.cpp
@@ -1473,3 +1473,10 @@
}
static_assert(g()); // expected-error {{constant expression}} expected-note
{{in call}}
}
+
+enum E { e1=-4, e2=4};
+void testValueInRangeOfEnumerationValues() {
+ constexpr E x1 = static_cast<E>(8); // expected-error {{must be initialized
by a constant expression}}
+ // expected-note@-1 {{store of value outside of the range of unscoped enum,
valid values -8 to 7}}
+ constexpr E x2 = static_cast<E>(-8);
+}
Index: clang/lib/AST/ExprConstant.cpp
===================================================================
--- clang/lib/AST/ExprConstant.cpp
+++ clang/lib/AST/ExprConstant.cpp
@@ -13509,6 +13509,46 @@
return Info.Ctx.getTypeSize(DestType) == Info.Ctx.getTypeSize(SrcType);
}
+ if (Info.Ctx.getLangOpts().CPlusPlus20)
+ if (const EnumType *ET = dyn_cast<EnumType>(DestType)) {
+ const EnumDecl *ED = ET->getDecl();
+ // Check that the value is within the range of the enumeration values.
+ //
+ // This corressponds to [expr.static.cast]p10 which says:
+ // A value of integral or enumeration type can be explicitly converted
+ // to a complete enumeration type ... If the enumeration type does not
+ // have a fixed underlying type, the value is unchanged if the original
+ // value is within the range of the enumeration values ([dcl.enum]),
and
+ // otherwise, the behavior is undefined.
+ //
+ // This was resolved as part of DR2338 which has CD5 status.
+ if (!ED->isFixed()) {
+ llvm::APInt Min;
+ llvm::APInt End;
+
+ unsigned Bitwidth = Info.Ctx.getIntWidth(DestType);
+ unsigned NumNegativeBits = ED->getNumNegativeBits();
+ unsigned NumPositiveBits = ED->getNumPositiveBits();
+
+ if (NumNegativeBits) {
+ unsigned NumBits = std::max(NumNegativeBits, NumPositiveBits + 1);
+ End = llvm::APInt(Bitwidth, 1) << (NumBits - 1);
+ Min = -End;
+ } else {
+ End = llvm::APInt(Bitwidth, 1) << NumPositiveBits;
+ Min = llvm::APInt::getZero(Bitwidth);
+ }
+
+ if (NumNegativeBits &&
+ (End.sle(Result.getInt()) || Min.sgt(Result.getInt())))
+ CCEDiag(E, diag::note_constexpr_unscoped_enum_out_of_range)
+ << Min.getSExtValue() << (End.getSExtValue() - 1);
+ else if (!NumNegativeBits && End.ule(Result.getInt()))
+ CCEDiag(E, diag::note_constexpr_unscoped_enum_out_of_range)
+ << Min.getZExtValue() << (End.getZExtValue() - 1);
+ }
+ }
+
return Success(HandleIntToIntCast(Info, E, DestType, SrcType,
Result.getInt()), E);
}
Index: clang/include/clang/Basic/DiagnosticASTKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticASTKinds.td
+++ clang/include/clang/Basic/DiagnosticASTKinds.td
@@ -366,6 +366,8 @@
"type %0 has unexpected layout">;
def note_constexpr_unsupported_flexible_array : Note<
"flexible array initialization is not yet supported">;
+def note_constexpr_unscoped_enum_out_of_range : Note<
+ "store of value outside of the range of unscoped enum, valid values %0 to
%1">;
def err_experimental_clang_interp_failed : Error<
"the experimental clang interpreter failed to evaluate an expression">;
Index: clang/test/SemaCXX/constant-expression-cxx2a.cpp
===================================================================
--- clang/test/SemaCXX/constant-expression-cxx2a.cpp
+++ clang/test/SemaCXX/constant-expression-cxx2a.cpp
@@ -1473,3 +1473,10 @@
}
static_assert(g()); // expected-error {{constant expression}} expected-note {{in call}}
}
+
+enum E { e1=-4, e2=4};
+void testValueInRangeOfEnumerationValues() {
+ constexpr E x1 = static_cast<E>(8); // expected-error {{must be initialized by a constant expression}}
+ // expected-note@-1 {{store of value outside of the range of unscoped enum, valid values -8 to 7}}
+ constexpr E x2 = static_cast<E>(-8);
+}
Index: clang/lib/AST/ExprConstant.cpp
===================================================================
--- clang/lib/AST/ExprConstant.cpp
+++ clang/lib/AST/ExprConstant.cpp
@@ -13509,6 +13509,46 @@
return Info.Ctx.getTypeSize(DestType) == Info.Ctx.getTypeSize(SrcType);
}
+ if (Info.Ctx.getLangOpts().CPlusPlus20)
+ if (const EnumType *ET = dyn_cast<EnumType>(DestType)) {
+ const EnumDecl *ED = ET->getDecl();
+ // Check that the value is within the range of the enumeration values.
+ //
+ // This corressponds to [expr.static.cast]p10 which says:
+ // A value of integral or enumeration type can be explicitly converted
+ // to a complete enumeration type ... If the enumeration type does not
+ // have a fixed underlying type, the value is unchanged if the original
+ // value is within the range of the enumeration values ([dcl.enum]), and
+ // otherwise, the behavior is undefined.
+ //
+ // This was resolved as part of DR2338 which has CD5 status.
+ if (!ED->isFixed()) {
+ llvm::APInt Min;
+ llvm::APInt End;
+
+ unsigned Bitwidth = Info.Ctx.getIntWidth(DestType);
+ unsigned NumNegativeBits = ED->getNumNegativeBits();
+ unsigned NumPositiveBits = ED->getNumPositiveBits();
+
+ if (NumNegativeBits) {
+ unsigned NumBits = std::max(NumNegativeBits, NumPositiveBits + 1);
+ End = llvm::APInt(Bitwidth, 1) << (NumBits - 1);
+ Min = -End;
+ } else {
+ End = llvm::APInt(Bitwidth, 1) << NumPositiveBits;
+ Min = llvm::APInt::getZero(Bitwidth);
+ }
+
+ if (NumNegativeBits &&
+ (End.sle(Result.getInt()) || Min.sgt(Result.getInt())))
+ CCEDiag(E, diag::note_constexpr_unscoped_enum_out_of_range)
+ << Min.getSExtValue() << (End.getSExtValue() - 1);
+ else if (!NumNegativeBits && End.ule(Result.getInt()))
+ CCEDiag(E, diag::note_constexpr_unscoped_enum_out_of_range)
+ << Min.getZExtValue() << (End.getZExtValue() - 1);
+ }
+ }
+
return Success(HandleIntToIntCast(Info, E, DestType, SrcType,
Result.getInt()), E);
}
Index: clang/include/clang/Basic/DiagnosticASTKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticASTKinds.td
+++ clang/include/clang/Basic/DiagnosticASTKinds.td
@@ -366,6 +366,8 @@
"type %0 has unexpected layout">;
def note_constexpr_unsupported_flexible_array : Note<
"flexible array initialization is not yet supported">;
+def note_constexpr_unscoped_enum_out_of_range : Note<
+ "store of value outside of the range of unscoped enum, valid values %0 to %1">;
def err_experimental_clang_interp_failed : Error<
"the experimental clang interpreter failed to evaluate an expression">;
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