Diagnose uninitialized uses of a variable within its own initializer.

This is basically the same idea as the warning on uninitialized uses of
fields within an initializer list. As such, it is on by default and
under -Wuninitialized.

Original patch by Richard Trieu, with some massaging from me on the
wording and grouping of the diagnostics.

llvm-svn: 128376

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -871,6 +871,9 @@ def note_uninit_reference_member : Note<
   "uninitialized reference member is here">;
 def warn_field_is_uninit : Warning<"field is uninitialized when used here">,
   InGroup<Uninitialized>;
+def warn_uninit_self_reference_in_init : Warning<
+  "variable %0 is uninitialized when used within its own initialization">,
+  InGroup<Uninitialized>;
 def warn_uninit_var : Warning<"variable %0 is possibly uninitialized when used here">,
   InGroup<Uninitialized>, DefaultIgnore;
 def warn_maybe_uninit_var :

clang/lib/Sema/SemaDecl.cpp

@@ -25,6 +25,7 @@
 #include "clang/AST/DeclCXX.h"
 #include "clang/AST/DeclObjC.h"
 #include "clang/AST/DeclTemplate.h"
+#include "clang/AST/EvaluatedExprVisitor.h"
 #include "clang/AST/ExprCXX.h"
 #include "clang/AST/StmtCXX.h"
 #include "clang/AST/CharUnits.h"
@@ -4664,6 +4665,46 @@ bool Sema::CheckForConstantInitializer(Expr *Init, QualType DclT) {
   return true;
 }
 
+namespace {
+  // Visits an initialization expression to see if OrigDecl is evaluated in
+  // its own initialization and throws a warning if it does.
+  class SelfReferenceChecker
+      : public EvaluatedExprVisitor<SelfReferenceChecker> {
+    Sema &S;
+    Decl *OrigDecl;
+
+  public:
+    typedef EvaluatedExprVisitor<SelfReferenceChecker> Inherited;
+
+    SelfReferenceChecker(Sema &S, Decl *OrigDecl) : Inherited(S.Context),
+                                                    S(S), OrigDecl(OrigDecl) { }
+
+    void VisitExpr(Expr *E) {
+      if (isa<ObjCMessageExpr>(*E)) return;
+      Inherited::VisitExpr(E);
+    }
+
+    void VisitImplicitCastExpr(ImplicitCastExpr *E) {
+      CheckForSelfReference(E);
+      Inherited::VisitImplicitCastExpr(E);
+    }
+
+    void CheckForSelfReference(ImplicitCastExpr *E) {
+      if (E->getCastKind() != CK_LValueToRValue) return;
+      Expr* SubExpr = E->getSubExpr()->IgnoreParenImpCasts();
+      DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(SubExpr);
+      if (!DRE) return;
+      Decl* ReferenceDecl = DRE->getDecl();
+      if (OrigDecl != ReferenceDecl) return;
+      LookupResult Result(S, DRE->getNameInfo(), Sema::LookupOrdinaryName,
+                          Sema::NotForRedeclaration);
+      S.Diag(SubExpr->getLocStart(), diag::warn_uninit_self_reference_in_init)
+        << Result.getLookupName() << OrigDecl->getLocation()
+        << SubExpr->getSourceRange();
+    }
+  };
+}
+
 /// AddInitializerToDecl - Adds the initializer Init to the
 /// declaration dcl. If DirectInit is true, this is C++ direct
 /// initialization rather than copy initialization.
@@ -4674,6 +4715,8 @@ void Sema::AddInitializerToDecl(Decl *RealDecl, Expr *Init,
   if (RealDecl == 0 || RealDecl->isInvalidDecl())
     return;
 
+  SelfReferenceChecker(*this, RealDecl).VisitExpr(Init);
+
   if (CXXMethodDecl *Method = dyn_cast<CXXMethodDecl>(RealDecl)) {
     // With declarators parsed the way they are, the parser cannot
     // distinguish between a normal initializer and a pure-specifier.
@@ -5231,7 +5274,7 @@ Sema::FinalizeDeclaratorGroup(Scope *S, const DeclSpec &DS,
     if (Decl *D = Group[i])
       Decls.push_back(D);
 
-  return BuildDeclaratorGroup(Decls.data(), Decls.size(), 
+  return BuildDeclaratorGroup(Decls.data(), Decls.size(),
                               DS.getTypeSpecType() == DeclSpec::TST_auto);
 }
 

clang/test/PCH/pragma-diag-section.cpp

@@ -12,7 +12,10 @@
 #pragma clang diagnostic ignored "-Wtautological-compare"
 template <typename T>
 struct TS {
-    void m() { T b = b==b; }
+    void m() {
+      T a = 0;
+      T b = a==a;
+    }
 };
 #pragma clang diagnostic pop
 

clang/test/PCH/pragma-diag.c

@@ -13,7 +13,8 @@
 #else
 
 void f() {
-  int b = b==b;
+  int a = 0;
+  int b = a==a;
 }
 
 #endif

clang/test/PCH/rdar8852495.c

@@ -16,7 +16,8 @@
 #else
 
 int f() {
-  int b = b==b;
+  int a;
+  int b = a==a;
   unsigned x;
   signed y;
   return x == y;

clang/test/Preprocessor/pragma_diagnostic_sections.cpp

@@ -2,14 +2,14 @@
 
 // rdar://8365684
 struct S {
-    void m1() { int b = b==b; } // expected-warning {{always evaluates to true}}
+    void m1() { int b; while (b==b); } // expected-warning {{always evaluates to true}}
 
 #pragma clang diagnostic push
 #pragma clang diagnostic ignored "-Wtautological-compare"
-    void m2() { int b = b==b; }
+    void m2() { int b; while (b==b); }
 #pragma clang diagnostic pop
 
-    void m3() { int b = b==b; } // expected-warning {{always evaluates to true}}
+    void m3() { int b; while (b==b); } // expected-warning {{always evaluates to true}}
 };
 
 //------------------------------------------------------------------------------
@@ -18,7 +18,7 @@ struct S {
 #pragma clang diagnostic ignored "-Wtautological-compare"
 template <typename T>
 struct TS {
-    void m() { T b = b==b; }
+    void m() { T b; while (b==b); }
 };
 #pragma clang diagnostic pop