[clang] 8de5137 - [Clang] Tighten restrictions on enum out of range diagnostic to avoid constant initialization

[Shafik Yaghmour via cfe-commits]

Author: Shafik Yaghmour
Date: 2022-08-17T14:14:00-07:00
New Revision: 8de51375f12d91675a18d17f262276e65f43fbe0

URL: https://github.com/llvm/llvm-project/commit/8de51375f12d91675a18d17f262276e65f43fbe0
DIFF: https://github.com/llvm/llvm-project/commit/8de51375f12d91675a18d17f262276e65f43fbe0.diff

LOG: [Clang] Tighten restrictions on enum out of range diagnostic to avoid constant initialization

The restrictions added in D131704 were not sufficient to avoid all non-constant
expression contexts. In particular constant initialization cases.

We need to check EvaluatingDecl to detect if the variable we are initializing is
constexpr or not.

At this point it looks like this is the remaining case affecting various projects
with this diagnostic.

Differential Revision: https://reviews.llvm.org/D131874

Added: 
    

Modified: 
    clang/lib/AST/ExprConstant.cpp
    clang/test/SemaCXX/constant-expression-cxx11.cpp
    clang/test/SemaCXX/cxx2a-consteval.cpp

Removed: 
    


################################################################################
diff  --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index f8de0f28d1840..3df0e4292b6ca 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -13536,6 +13536,18 @@ bool IntExprEvaluator::VisitCastExpr(const CastExpr *E) {
     if (Info.Ctx.getLangOpts().CPlusPlus && Info.InConstantContext &&
         Info.EvalMode == EvalInfo::EM_ConstantExpression &&
         DestType->isEnumeralType()) {
+
+      bool ConstexprVar = true;
+
+      // We know if we are here that we are in a context that we might require
+      // a constant expression or a context that requires a constant
+      // value. But if we are initializing a value we don't know if it is a
+      // constexpr variable or not. We can check the EvaluatingDecl to determine
+      // if it constexpr or not. If not then we don't want to emit a diagnostic.
+      if (const auto *VD = dyn_cast_or_null<VarDecl>(
+              Info.EvaluatingDecl.dyn_cast<const ValueDecl *>()))
+        ConstexprVar = VD->isConstexpr();
+
       const EnumType *ET = dyn_cast<EnumType>(DestType.getCanonicalType());
       const EnumDecl *ED = ET->getDecl();
       // Check that the value is within the range of the enumeration values.
@@ -13555,13 +13567,14 @@ bool IntExprEvaluator::VisitCastExpr(const CastExpr *E) {
         ED->getValueRange(Max, Min);
         --Max;
 
-        if (ED->getNumNegativeBits() &&
+        if (ED->getNumNegativeBits() && ConstexprVar &&
             (Max.slt(Result.getInt().getSExtValue()) ||
              Min.sgt(Result.getInt().getSExtValue())))
-          Info.Ctx.getDiagnostics().Report(E->getExprLoc(),
-                                       diag::warn_constexpr_unscoped_enum_out_of_range)
-	       << llvm::toString(Result.getInt(),10) << Min.getSExtValue() << Max.getSExtValue();
-        else if (!ED->getNumNegativeBits() &&
+          Info.Ctx.getDiagnostics().Report(
+              E->getExprLoc(), diag::warn_constexpr_unscoped_enum_out_of_range)
+              << llvm::toString(Result.getInt(), 10) << Min.getSExtValue()
+              << Max.getSExtValue();
+        else if (!ED->getNumNegativeBits() && ConstexprVar &&
                  Max.ult(Result.getInt().getZExtValue()))
           Info.Ctx.getDiagnostics().Report(E->getExprLoc(),
                                        diag::warn_constexpr_unscoped_enum_out_of_range)

diff  --git a/clang/test/SemaCXX/constant-expression-cxx11.cpp b/clang/test/SemaCXX/constant-expression-cxx11.cpp
index c4f64ff9cd30a..4b856d319c3d5 100644
--- a/clang/test/SemaCXX/constant-expression-cxx11.cpp
+++ b/clang/test/SemaCXX/constant-expression-cxx11.cpp
@@ -2419,6 +2419,13 @@ enum class EScoped {escoped1=-4, escoped2=4};
 
 enum EMaxInt {emaxint1=-1, emaxint2=__INT_MAX__};
 
+enum NumberType {};
+
+E2 testDefaultArgForParam(E2 e2Param = (E2)-1) { // ok, not a constant expression context
+  E2 e2LocalInit = e2Param; // ok, not a constant expression context
+  return e2LocalInit;
+}
+
 void testValueInRangeOfEnumerationValues() {
   constexpr E1 x1 = static_cast<E1>(-8);
   constexpr E1 x2 = static_cast<E1>(8);
@@ -2454,6 +2461,8 @@ void testValueInRangeOfEnumerationValues() {
   constexpr EMaxInt x19 = static_cast<EMaxInt>(__INT_MAX__-1);
   constexpr EMaxInt x20 = static_cast<EMaxInt>((long)__INT_MAX__+1);
   // expected-error at -1 {{integer value 2147483648 is outside the valid range of values [-2147483648, 2147483647] for this enumeration type}}
+
+  const NumberType neg_one = (NumberType) ((NumberType) 0 - (NumberType) 1); // ok, not a constant expression context
 }
 
 enum SortOrder {
@@ -2470,3 +2479,8 @@ void A::f(SortOrder order) {
     return;
 }
 }
+
+GH50055::E2 GlobalInitNotCE1 = (GH50055::E2)-1; // ok, not a constant expression context
+GH50055::E2 GlobalInitNotCE2 = GH50055::testDefaultArgForParam(); // ok, not a constant expression context
+constexpr GH50055::E2 GlobalInitCE = (GH50055::E2)-1;
+// expected-error at -1 {{integer value -1 is outside the valid range of values [0, 7] for this enumeration type}}

diff  --git a/clang/test/SemaCXX/cxx2a-consteval.cpp b/clang/test/SemaCXX/cxx2a-consteval.cpp
index 8438413b6f4a8..4251d82c17e60 100644
--- a/clang/test/SemaCXX/cxx2a-consteval.cpp
+++ b/clang/test/SemaCXX/cxx2a-consteval.cpp
@@ -865,3 +865,15 @@ consteval int aConstevalFunction() { // expected-error {{consteval function neve
 }
 
 } // namespace multiple_default_constructors
+
+namespace GH50055 {
+enum E {e1=0, e2=1};
+consteval int testDefaultArgForParam(E eParam = (E)-1) {
+// expected-error at -1 {{integer value -1 is outside the valid range of values [0, 1] for this enumeration type}}
+  return (int)eParam;
+}
+
+int test() {
+  return testDefaultArgForParam() + testDefaultArgForParam((E)1);
+}
+}