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.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@128376 91177308-0d34-0410-b5e6-96231b3b80d8

6 files changed, 59 insertions, 8 deletions

diff --git a/include/clang/Basic/DiagnosticSemaKinds.td b/include/clang/Basic/DiagnosticSemaKinds.td
index 55223ac134..6e0bec2f1f 100644
--- a/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/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 :
diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index 59b4f5f229..7a1492a53b 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/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);
 }
 
diff --git a/test/PCH/pragma-diag-section.cpp b/test/PCH/pragma-diag-section.cpp
index 312f720ebd..5b996bb2f0 100644
--- a/test/PCH/pragma-diag-section.cpp
+++ b/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
 
diff --git a/test/PCH/pragma-diag.c b/test/PCH/pragma-diag.c
index c517103640..b304c4bf8c 100644
--- a/test/PCH/pragma-diag.c
+++ b/test/PCH/pragma-diag.c
@@ -13,7 +13,8 @@
 #else
 
 void f() {
-  int b = b==b;
+  int a = 0;
+  int b = a==a;
 }
 
 #endif
diff --git a/test/PCH/rdar8852495.c b/test/PCH/rdar8852495.c
index 2d49e001b0..fb465a37ce 100644
--- a/test/PCH/rdar8852495.c
+++ b/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;
diff --git a/test/Preprocessor/pragma_diagnostic_sections.cpp b/test/Preprocessor/pragma_diagnostic_sections.cpp
index 69436b0bd8..b680fae5b9 100644
--- a/test/Preprocessor/pragma_diagnostic_sections.cpp
+++ b/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