[PATCH] D23493: Fix PR28366: Teach the const-expression evaluator to be more fault tolerant with non-const enclosing local variables, or otherwise fold them if const.

[Faisal Vali via cfe-commits]

faisalv removed rL LLVM as the repository for this revision.
faisalv updated this revision to Diff 68091.
faisalv added a comment.

Updated the patch per Richard's direction (which helped clarify my thinking about this): Check only the current call frame - if the VarDecl is contained within the current callee - only then does it make sense to dig into the stack-variables of the frame.  No other scenario really makes sense (even for lambdas, we care about the parent decl-contexts (static binding), not variables within the call-frame stack (run-time binding).

Thanks Richard.


https://reviews.llvm.org/D23493

Files:
  lib/AST/ExprConstant.cpp
  lib/Sema/SemaTemplateInstantiateDecl.cpp
  test/SemaCXX/constant-expression-cxx11.cpp

Index: test/SemaCXX/constant-expression-cxx11.cpp
===================================================================
--- test/SemaCXX/constant-expression-cxx11.cpp
+++ test/SemaCXX/constant-expression-cxx11.cpp
@@ -2066,3 +2066,33 @@
   constexpr Z z(1);
   static_assert(z.w == 1 && z.x == 2 && z.y == 3 && z.z == 4, "");
 }
+
+
+namespace PR28366 {
+namespace ns1 {
+
+void f(char c) { //expected-note2{{declared here}}
+  struct X {
+    static constexpr char f() { //expected-error{{never produces a constant expression}}
+      return c; //expected-error{{reference to local}} expected-note{{non-const variable}}
+    }
+  };
+  int I = X::f();
+}
+
+void g() {
+  const int c = 'c';
+  static const int d = 'd';
+  struct X {
+    static constexpr int f() {
+      return c + d;
+    }
+  };
+  constexpr int CD = X::f();
+}
+
+
+} // end ns1
+
+} //end ns PR28366
+
Index: lib/Sema/SemaTemplateInstantiateDecl.cpp
===================================================================
--- lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -187,7 +187,7 @@
 
   SmallVector<PartialDiagnosticAt, 8> Diags;
   if (A->getCond()->isValueDependent() && !Cond->isValueDependent() &&
-      !Expr::isPotentialConstantExprUnevaluated(Cond, cast<FunctionDecl>(Tmpl),
+      !Expr::isPotentialConstantExprUnevaluated(Cond, cast<FunctionDecl>(New),
                                                 Diags)) {
     S.Diag(A->getLocation(), diag::err_enable_if_never_constant_expr);
     for (int I = 0, N = Diags.size(); I != N; ++I)
Index: lib/AST/ExprConstant.cpp
===================================================================
--- lib/AST/ExprConstant.cpp
+++ lib/AST/ExprConstant.cpp
@@ -4788,10 +4788,19 @@
   return Error(E);
 }
 
+
 bool LValueExprEvaluator::VisitVarDecl(const Expr *E, const VarDecl *VD) {
   CallStackFrame *Frame = nullptr;
-  if (VD->hasLocalStorage() && Info.CurrentCall->Index > 1)
-    Frame = Info.CurrentCall;
+  if (VD->hasLocalStorage() && Info.CurrentCall->Index > 1) {
+    // Only if the DeclContext of VD is the same as the called function do we
+    // set the Frame to the Current CallStackFrame, so that we can find its
+    // associated value from the variable-objects associated with that frame.
+    if (Info.CurrentCall->Callee && isa<FunctionDecl>(VD->getDeclContext()) &&
+        cast<FunctionDecl>(VD->getDeclContext()->getRedeclContext())
+                ->getFirstDecl() == Info.CurrentCall->Callee->getFirstDecl()) {
+      Frame = Info.CurrentCall;
+    }
+  }
 
   if (!VD->getType()->isReferenceType()) {
     if (Frame) {


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