constexpr handling improvements. Produce detailed diagnostics when a 'constexpr'

variable is initialized by a non-constant expression, and pass in the variable
being declared so that earlier-initialized fields' values can be used.

Rearrange VarDecl init evaluation to make this possible, and in so doing fix a
long-standing issue in our C++ constant expression handling, where we would
mishandle cases like:

  extern const int a;
  const int n = a;
  const int a = 5;
  int arr[n];

Here, n is not initialized by a constant expression, so can't be used in an ICE,
even though the initialization expression would be an ICE if it appeared later
in the TU. This requires computing whether the initializer is an ICE eagerly,
and saving that information in PCH files.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@146856 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 31 insertions, 9 deletions

diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index a0291afeed..c31850313a 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -6539,17 +6539,39 @@ void Sema::CheckCompleteVariableDeclaration(VarDecl *var) {
   Expr *Init = var->getInit();
   bool IsGlobal = var->hasGlobalStorage() && !var->isStaticLocal();
 
-  if (!var->getDeclContext()->isDependentContext() &&
-      (var->isConstexpr() || IsGlobal) && Init &&
-      !Init->isConstantInitializer(Context, baseType->isReferenceType())) {
-    // FIXME: Improve this diagnostic to explain why the initializer is not
-    // a constant expression.
-    if (var->isConstexpr())
-      Diag(var->getLocation(), diag::err_constexpr_var_requires_const_init)
-        << var << Init->getSourceRange();
-    if (IsGlobal)
+  if (!var->getDeclContext()->isDependentContext() && Init) {
+    if (IsGlobal && !var->isConstexpr() &&
+        getDiagnostics().getDiagnosticLevel(diag::warn_global_constructor,
+                                            var->getLocation())
+          != DiagnosticsEngine::Ignored &&
+        !Init->isConstantInitializer(Context, baseType->isReferenceType()))
       Diag(var->getLocation(), diag::warn_global_constructor)
         << Init->getSourceRange();
+
+    QualType Type = var->getType();
+    if (var->isConstexpr()) {
+      llvm::SmallVector<PartialDiagnosticAt, 8> Notes;
+      if (!var->evaluateValue(Notes) || !var->isInitICE()) {
+        SourceLocation DiagLoc = var->getLocation();
+        // If the note doesn't add any useful information other than a source
+        // location, fold it into the primary diagnostic.
+        if (Notes.size() == 1 && Notes[0].second.getDiagID() ==
+              diag::note_invalid_subexpr_in_const_expr) {
+          DiagLoc = Notes[0].first;
+          Notes.clear();
+        }
+        Diag(DiagLoc, diag::err_constexpr_var_requires_const_init)
+          << var << Init->getSourceRange();
+        for (unsigned I = 0, N = Notes.size(); I != N; ++I)
+          Diag(Notes[I].first, Notes[I].second);
+      }
+    } else if (getLangOptions().CPlusPlus && !Type.isVolatileQualified() &&
+               Type.isConstQualified() && Type->isIntegralOrEnumerationType()) {
+      // Check whether the initializer of a const variable of integral or
+      // enumeration type is an ICE now, since we can't tell whether it was
+      // initialized by a constant expression if we check later.
+      var->checkInitIsICE();
+    }
   }
 
   // Require the destructor.