Added a warning when referencing an if's condition variable in the

"else" clause, e.g.,

  if (int X = foo()) {
  } else {
    if (X) { // warning: X is always zero in this context
    }
  }

Fixes rdar://6425550 and lets me think about something other than
DeclContext.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@60858 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 28 insertions, 0 deletions

diff --git a/lib/Parse/ParseStmt.cpp b/lib/Parse/ParseStmt.cpp
index 8b5277bc36..cb35740465 100644
--- a/lib/Parse/ParseStmt.cpp
+++ b/lib/Parse/ParseStmt.cpp
@@ -509,8 +509,11 @@ Parser::StmtResult Parser::ParseIfStatement() {
     ParseScope InnerScope(this, Scope::DeclScope, 
                           C99orCXX && Tok.isNot(tok::l_brace));
 
+    bool WithinElse = CurScope->isWithinElse();
+    CurScope->setWithinElse(true);
     ElseStmtLoc = Tok.getLocation();
     ElseStmt = ParseStatement();
+    CurScope->setWithinElse(WithinElse);
 
     // Pop the 'else' scope if needed.
     InnerScope.Exit();
diff --git a/lib/Sema/SemaExpr.cpp b/lib/Sema/SemaExpr.cpp
index 8cbbca3fbf..3870f0736e 100644
--- a/lib/Sema/SemaExpr.cpp
+++ b/lib/Sema/SemaExpr.cpp
@@ -483,6 +483,27 @@ Sema::ExprResult Sema::ActOnDeclarationNameExpr(Scope *S, SourceLocation Loc,
   // check if referencing an identifier with __attribute__((deprecated)).
   if (VD->getAttr<DeprecatedAttr>())
     Diag(Loc, diag::warn_deprecated) << VD->getDeclName();
+  
+  if (VarDecl *Var = dyn_cast<VarDecl>(VD)) {
+    if (Var->isDeclaredInCondition() && Var->getType()->isScalarType()) {
+      Scope *CheckS = S;
+      while (CheckS) {
+        if (CheckS->isWithinElse() && 
+            CheckS->getControlParent()->isDeclScope(Var)) {
+          if (Var->getType()->isBooleanType())
+            Diag(Loc, diag::warn_value_always_false) << Var->getDeclName();
+          else
+            Diag(Loc, diag::warn_value_always_zero) << Var->getDeclName();
+          break;
+        }
+
+        // Move up one more control parent to check again.
+        CheckS = CheckS->getControlParent();
+        if (CheckS)
+          CheckS = CheckS->getParent();
+      }
+    }
+  }
 
   // Only create DeclRefExpr's for valid Decl's.
   if (VD->isInvalidDecl())
diff --git a/lib/Sema/SemaExprCXX.cpp b/lib/Sema/SemaExprCXX.cpp
index c4cab3316b..27b0ba34d1 100644
--- a/lib/Sema/SemaExprCXX.cpp
+++ b/lib/Sema/SemaExprCXX.cpp
@@ -648,6 +648,10 @@ Sema::ActOnCXXConditionDeclarationExpr(Scope *S, SourceLocation StartLoc,
     return true;
   AddInitializerToDecl(Dcl, AssignExprVal);
 
+  // Mark this variable as one that is declared within a conditional.
+  if (VarDecl *VD = dyn_cast<VarDecl>((Decl *)Dcl))
+    VD->setDeclaredInCondition(true);
+
   return new CXXConditionDeclExpr(StartLoc, EqualLoc,
                                        cast<VarDecl>(static_cast<Decl *>(Dcl)));
 }