[PATCH] D137563: [clang][Interp] Check declarations for constexpr-ness in Load() instructions

[Timm Bäder via Phabricator via cfe-commits]

tbaeder created this revision.
tbaeder added reviewers: aaron.ballman, erichkeane, tahonermann, shafik.
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Refering to non-constexpr variables in a constant expression is (apparently) just fine, and only problematic once we load a value.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D137563

Files:
  clang/lib/AST/Interp/Interp.cpp
  clang/test/AST/Interp/records.cpp


Index: clang/test/AST/Interp/records.cpp
===================================================================
--- clang/test/AST/Interp/records.cpp
+++ clang/test/AST/Interp/records.cpp
@@ -29,6 +29,15 @@
 
 static_assert(Ints::getFive() == 5, "");
 
+// Read of a non-constexpr variable in a constant expression.
+BoolPair nonConstBP; // ref-note {{declared here}} \
+                     // expected-note {{declared here}}
+constexpr BoolPair *constBP = &nonConstBP;
+static_assert(constBP->first, ""); // 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}}
+
 constexpr Ints ints;
 static_assert(ints.a == 20, "");
 static_assert(ints.b == 30, "");
Index: clang/lib/AST/Interp/Interp.cpp
===================================================================
--- clang/lib/AST/Interp/Interp.cpp
+++ clang/lib/AST/Interp/Interp.cpp
@@ -98,6 +98,26 @@
   return true;
 }
 
+static bool CheckConstexpr(InterpState &S, CodePtr OpPC, const Pointer &Ptr) {
+  if (!S.inConstantContext())
+    return true;
+
+  auto *VD = Ptr.getDeclDesc()->asValueDecl();
+  if (!VD)
+    return true;
+
+  if (auto *VarD = dyn_cast<VarDecl>(VD)) {
+    if (VarD->hasLocalStorage() || VarD->isConstexpr())
+      return true;
+  }
+
+  const SourceInfo &Loc = S.Current->getSource(OpPC);
+  S.FFDiag(Loc, diag::note_constexpr_ltor_non_constexpr, 1) << VD;
+  S.Note(VD->getLocation(), diag::note_declared_at);
+
+  return false;
+}
+
 static bool CheckInitialized(InterpState &S, CodePtr OpPC, const Pointer &Ptr,
                              AccessKinds AK) {
   if (Ptr.isInitialized())
@@ -294,6 +314,8 @@
     return false;
   if (!CheckExtern(S, OpPC, Ptr))
     return false;
+  if (!CheckConstexpr(S, OpPC, Ptr))
+    return false;
   if (!CheckRange(S, OpPC, Ptr, AK_Read))
     return false;
   if (!CheckInitialized(S, OpPC, Ptr, AK_Read))


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