Fix to PR8880 (clang dies processing a for loop)

Due to statement expressions supported as GCC extension, it is possible
to put 'break' or 'continue' into a loop/switch statement but outside
its body, for example:

    for ( ; ({ if (first) { first = 0; continue; } 0; }); )

This code is rejected by GCC if compiled in C mode but is accepted in C++
code. GCC bug 44715 tracks this discrepancy. Clang used code generation
that differs from GCC in both modes: only statement of the third
expression of 'for' behaves as if it was inside loop body.

This change makes code generation more close to GCC, considering 'break'
or 'continue' statement in condition and increment expressions of a
loop as it was inside the loop body. It also adds error for the cases
when 'break'/'continue' appear outside loop due to this syntax. If
code generation differ from GCC, warning is issued.

Differential Revision: http://llvm-reviews.chandlerc.com/D2518

llvm-svn: 199897

2 files changed, 59 insertions, 12 deletions

diff --git a/clang/lib/Sema/Scope.cpp b/clang/lib/Sema/Scope.cpp
index 10f12ce844f..eef55d31947 100644
--- a/clang/lib/Sema/Scope.cpp
+++ b/clang/lib/Sema/Scope.cpp
@@ -69,3 +69,18 @@ bool Scope::containedInPrototypeScope() const {
   }
   return false;
 }
+
+void Scope::AddFlags(unsigned FlagsToSet) {
+  assert((FlagsToSet & ~(BreakScope | ContinueScope)) == 0 &&
+         "Unsupported scope flags");
+  if (FlagsToSet & BreakScope) {
+    assert((Flags & BreakScope) == 0 && "Already set");
+    BreakParent = this;
+  }
+  if (FlagsToSet & ContinueScope) {
+    assert((Flags & ContinueScope) == 0 && "Already set");
+    ContinueParent = this;
+  }
+  Flags |= FlagsToSet;
+}
+
diff --git a/clang/lib/Sema/SemaStmt.cpp b/clang/lib/Sema/SemaStmt.cpp
index 34a0f84e8f3..badd048bd87 100644
--- a/clang/lib/Sema/SemaStmt.cpp
+++ b/clang/lib/Sema/SemaStmt.cpp
@@ -1205,6 +1205,7 @@ Sema::ActOnWhileStmt(SourceLocation WhileLoc, FullExprArg Cond,
   Expr *ConditionExpr = CondResult.take();
   if (!ConditionExpr)
     return StmtError();
+  CheckBreakContinueBinding(ConditionExpr);
 
   DiagnoseUnusedExprResult(Body);
 
@@ -1221,6 +1222,7 @@ Sema::ActOnDoStmt(SourceLocation DoLoc, Stmt *Body,
                   Expr *Cond, SourceLocation CondRParen) {
   assert(Cond && "ActOnDoStmt(): missing expression");
 
+  CheckBreakContinueBinding(Cond);
   ExprResult CondResult = CheckBooleanCondition(Cond, DoLoc);
   if (CondResult.isInvalid())
     return StmtError();
@@ -1483,25 +1485,33 @@ namespace {
     return false;
   }
 
-  // A visitor to determine if a continue statement is a subexpression.
-  class ContinueFinder : public EvaluatedExprVisitor<ContinueFinder> {
-    bool Found;
+  // A visitor to determine if a continue or break statement is a
+  // subexpression.
+  class BreakContinueFinder : public EvaluatedExprVisitor<BreakContinueFinder> {
+    SourceLocation BreakLoc;
+    SourceLocation ContinueLoc;
   public:
-    ContinueFinder(Sema &S, Stmt* Body) :
-        Inherited(S.Context),
-        Found(false) {
+    BreakContinueFinder(Sema &S, Stmt* Body) :
+        Inherited(S.Context) {
       Visit(Body);
     }
 
-    typedef EvaluatedExprVisitor<ContinueFinder> Inherited;
+    typedef EvaluatedExprVisitor<BreakContinueFinder> Inherited;
 
     void VisitContinueStmt(ContinueStmt* E) {
-      Found = true;
+      ContinueLoc = E->getContinueLoc();
+    }
+
+    void VisitBreakStmt(BreakStmt* E) {
+      BreakLoc = E->getBreakLoc();
     }
 
-    bool ContinueFound() { return Found; }
+    bool ContinueFound() { return ContinueLoc.isValid(); }
+    bool BreakFound() { return BreakLoc.isValid(); }
+    SourceLocation GetContinueLoc() { return ContinueLoc; }
+    SourceLocation GetBreakLoc() { return BreakLoc; }
 
-  };  // end class ContinueFinder
+  };  // end class BreakContinueFinder
 
   // Emit a warning when a loop increment/decrement appears twice per loop
   // iteration.  The conditions which trigger this warning are:
@@ -1530,11 +1540,11 @@ namespace {
     if (!ProcessIterationStmt(S, LastStmt, LastIncrement, LastDRE)) return;
 
     // Check that the two statements are both increments or both decrements
-    // on the same varaible.
+    // on the same variable.
     if (LoopIncrement != LastIncrement ||
         LoopDRE->getDecl() != LastDRE->getDecl()) return;
 
-    if (ContinueFinder(S, Body).ContinueFound()) return;
+    if (BreakContinueFinder(S, Body).ContinueFound()) return;
 
     S.Diag(LastDRE->getLocation(), diag::warn_redundant_loop_iteration)
          << LastDRE->getDecl() << LastIncrement;
@@ -1544,6 +1554,25 @@ namespace {
 
 } // end namespace
 
+
+void Sema::CheckBreakContinueBinding(Expr *E) {
+  if (!E || getLangOpts().CPlusPlus)
+    return;
+  BreakContinueFinder BCFinder(*this, E);
+  Scope *BreakParent = CurScope->getBreakParent();
+  if (BCFinder.BreakFound() && BreakParent) {
+    if (BreakParent->getFlags() & Scope::SwitchScope) {
+      Diag(BCFinder.GetBreakLoc(), diag::warn_break_binds_to_switch);
+    } else {
+      Diag(BCFinder.GetBreakLoc(), diag::warn_loop_ctrl_binds_to_inner)
+          << "break";
+    }
+  } else if (BCFinder.ContinueFound() && CurScope->getContinueParent()) {
+    Diag(BCFinder.GetContinueLoc(), diag::warn_loop_ctrl_binds_to_inner)
+        << "continue";
+  }
+}
+
 StmtResult
 Sema::ActOnForStmt(SourceLocation ForLoc, SourceLocation LParenLoc,
                    Stmt *First, FullExprArg second, Decl *secondVar,
@@ -1567,6 +1596,9 @@ Sema::ActOnForStmt(SourceLocation ForLoc, SourceLocation LParenLoc,
     }
   }
 
+  CheckBreakContinueBinding(second.get());
+  CheckBreakContinueBinding(third.get());
+
   CheckForLoopConditionalStatement(*this, second.get(), third.get(), Body);
   CheckForRedundantIteration(*this, third.get(), Body);