[clang][Interp] Diagnose more unkonwn DeclRefExprs

[tbaeder]

Summary

Diagnose used non-const and/or extern globals.

[aaron.ballman]

LG aside from a nit.

clang/lib/AST/Interp/Interp.cpp

558–561

Plus reformatting.

[tbaeder]

Looks like I squashed this into https://reviews.llvm.org/D156509 for some reason.

clang/lib/AST/Interp/Interp.cpp

bool CheckDeclRef(InterpState &S, CodePtr OpPC, const DeclRefExpr *DR) {
   const SourceInfo &E = S.Current->getSource(OpPC);
 
   if (isa<ParmVarDecl>(D)) {
     S.FFDiag(E, diag::note_constexpr_function_param_value_unknown) << D;
     S.Note(D->getLocation(), diag::note_declared_at) << D->getSourceRange();
     return false;
   }
 
+  if (const auto *VD = dyn_cast<VarDecl>(D)) {
+    if (!VD->getType().isConstant(S.getCtx())) {
+      if (VD->getType()->isIntegralOrEnumerationType())
+        S.FFDiag(E, diag::note_constexpr_ltor_non_const_int, 1) << VD;
+      else
+        S.FFDiag(E, diag::note_constexpr_ltor_non_constexpr, 1) << VD;
+
+      S.Note(VD->getLocation(), diag::note_declared_at) << VD->getSourceRange();
+      return false;
+    }
+
+    // const, but no initializer.
+    if (!VD->getAnyInitializer()) {
+      S.FFDiag(E, diag::note_constexpr_var_init_unknown, 1) << VD;
+      S.Note(VD->getLocation(), diag::note_declared_at) << VD->getSourceRange();
+      return false;
+    }
+  }
+
   return false;
 }
 
 bool CheckBitcast(InterpState &S, CodePtr OpPC, unsigned IndeterminateBits,
                   bool TargetIsUCharOrByte) {
 
   // This is always fine.
   if (IndeterminateBits == 0)

clang/test/AST/Interp/literals.cpp

namespace PointerCasts {
   constexpr intptr_t A = (intptr_t)P; // ref-error {{must be initialized by a constant expression}} \
                                       // ref-note {{cast that performs the conversions of a reinterpret_cast}} \
                                       // expected-error {{must be initialized by a constant expression}} \
                                       // expected-note {{cast that performs the conversions of a reinterpret_cast}}
 
   int array[(intptr_t)(char*)0]; // ref-warning {{variable length array folded to constant array}} \
                                  // expected-warning {{variable length array folded to constant array}}
 }
+
+namespace InvalidDeclRefs {
+  bool b00; // ref-note {{declared here}} \
+            // expected-note {{declared here}}
+  static_assert(b00, ""); // ref-error {{not an integral constant expression}} \
+                          // ref-note {{read of non-const variable}} \
+                          // expected-error {{not an integral constant expression}} \
+                          // expected-note {{read of non-const variable}}
+
+  float b01; // ref-note {{declared here}} \
+             // expected-note {{declared here}}
+  static_assert(b01, ""); // ref-error {{not an integral constant expression}} \
+                          // ref-note {{read of non-constexpr variable}} \
+                          // expected-error {{not an integral constant expression}} \
+                          // expected-note {{read of non-constexpr variable}}
+
+  extern const int b02; // ref-note {{declared here}} \
+                        // expected-note {{declared here}}
+  static_assert(b02, ""); // ref-error {{not an integral constant expression}} \
+                          // ref-note {{initializer of 'b02' is unknown}} \
+                          // expected-error {{not an integral constant expression}} \
+                          // expected-note {{initializer of 'b02' is unknown}}
+
+  /// FIXME: This should also be diagnosed in the new interpreter.
+  int b03 = 3; // ref-note {{declared here}}
+  static_assert(b03, ""); // ref-error {{not an integral constant expression}} \
+                          // ref-note {{read of non-const variable}}
+}