Expand array bounds checking to work in the presence of unary & and *,

and to work with pointer arithmetic in addition to array indexing.

The new pointer arithmetic porition of the array bounds checking can be
turned on by -Warray-bounds-pointer-arithmetic (and is off by default).


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@136046 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 68 insertions, 21 deletions

diff --git a/lib/Sema/SemaChecking.cpp b/lib/Sema/SemaChecking.cpp
index 25256b0407..32d90bffc2 100644
--- a/lib/Sema/SemaChecking.cpp
+++ b/lib/Sema/SemaChecking.cpp
@@ -3467,43 +3467,87 @@ void Sema::CheckCastAlign(Expr *Op, QualType T, SourceRange TRange) {
     << TRange << Op->getSourceRange();
 }
 
-static void CheckArrayAccess_Check(Sema &S,
-                                   const clang::ArraySubscriptExpr *E) {
-  const Expr *BaseExpr = E->getBase()->IgnoreParenImpCasts();
+static const Type* getElementType(const Expr *BaseExpr) {
+  const Type* EltType = BaseExpr->getType().getTypePtr();
+  if (EltType->isAnyPointerType())
+    return EltType->getPointeeType().getTypePtr();
+  else if (EltType->isArrayType())
+    return EltType->getBaseElementTypeUnsafe();
+  return EltType;
+}
+
+void Sema::CheckArrayAccess(const Expr *BaseExpr, const Expr *IndexExpr,
+                            bool isSubscript) {
+  const Type* EffectiveType = getElementType(BaseExpr);
+  BaseExpr = BaseExpr->IgnoreParenCasts();
+  IndexExpr = IndexExpr->IgnoreParenCasts();
+
   const ConstantArrayType *ArrayTy =
-    S.Context.getAsConstantArrayType(BaseExpr->getType());
+    Context.getAsConstantArrayType(BaseExpr->getType());
   if (!ArrayTy)
     return;
 
-  const Expr *IndexExpr = E->getIdx();
   if (IndexExpr->isValueDependent())
     return;
   llvm::APSInt index;
-  if (!IndexExpr->isIntegerConstantExpr(index, S.Context))
+  if (!IndexExpr->isIntegerConstantExpr(index, Context))
     return;
 
   if (index.isUnsigned() || !index.isNegative()) {
     llvm::APInt size = ArrayTy->getSize();
     if (!size.isStrictlyPositive())
       return;
+
+    const Type* BaseType = getElementType(BaseExpr);
+    if (BaseType != EffectiveType) {
+      // Make sure we're comparing apples to apples when comparing index to size
+      uint64_t ptrarith_typesize = Context.getTypeSize(EffectiveType);
+      uint64_t array_typesize = Context.getTypeSize(BaseType);
+      if (ptrarith_typesize != array_typesize) {
+        // There's a cast to a different size type involved
+        uint64_t ratio = array_typesize / ptrarith_typesize;
+        if (ptrarith_typesize * ratio != array_typesize)
+          // If the size of the array's base type is not a multiple of the
+          // casted-to pointee type, the results of the pointer arithmetic
+          // may or may not point to something consistently meaningful or within a
+          // valid reference...
+          return;
+
+        size *= llvm::APInt(size.getBitWidth(), ratio);
+      }
+    }
+
     if (size.getBitWidth() > index.getBitWidth())
       index = index.sext(size.getBitWidth());
     else if (size.getBitWidth() < index.getBitWidth())
       size = size.sext(index.getBitWidth());
 
-    if (index.slt(size))
+    // For array subscripting the index must be less than size, but for pointer
+    // arithmetic also allow the index (offset) to be equal to size since
+    // computing the next address after the end of the array is legal and
+    // commonly done e.g. in C++ iterators and range-based for loops.
+    if (isSubscript ? index.slt(size) : index.sle(size))
       return;
 
-    S.DiagRuntimeBehavior(E->getBase()->getLocStart(), BaseExpr,
-                          S.PDiag(diag::warn_array_index_exceeds_bounds)
-                            << index.toString(10, true)
-                            << size.toString(10, true)
-                            << IndexExpr->getSourceRange());
+    unsigned DiagID = diag::warn_ptr_arith_exceeds_bounds;
+    if (isSubscript)
+      DiagID = diag::warn_array_index_exceeds_bounds;
+
+    DiagRuntimeBehavior(BaseExpr->getLocStart(), BaseExpr,
+                        PDiag(DiagID) << index.toString(10, true)
+                          << size.toString(10, true)
+                          << (unsigned)size.getLimitedValue(~0U)
+                          << IndexExpr->getSourceRange());
   } else {
-    S.DiagRuntimeBehavior(E->getBase()->getLocStart(), BaseExpr,
-                          S.PDiag(diag::warn_array_index_precedes_bounds)
-                            << index.toString(10, true)
-                            << IndexExpr->getSourceRange());
+    unsigned DiagID = diag::warn_array_index_precedes_bounds;
+    if (!isSubscript) {
+      DiagID = diag::warn_ptr_arith_precedes_bounds;
+      if (index.isNegative()) index = -index;
+    }
+
+    DiagRuntimeBehavior(BaseExpr->getLocStart(), BaseExpr,
+                        PDiag(DiagID) << index.toString(10, true)
+                          << IndexExpr->getSourceRange());
   }
 
   const NamedDecl *ND = NULL;
@@ -3512,18 +3556,21 @@ static void CheckArrayAccess_Check(Sema &S,
   if (const MemberExpr *ME = dyn_cast<MemberExpr>(BaseExpr))
     ND = dyn_cast<NamedDecl>(ME->getMemberDecl());
   if (ND)
-    S.DiagRuntimeBehavior(ND->getLocStart(), BaseExpr,
-                          S.PDiag(diag::note_array_index_out_of_bounds)
-                            << ND->getDeclName());
+    DiagRuntimeBehavior(ND->getLocStart(), BaseExpr,
+                        PDiag(diag::note_array_index_out_of_bounds)
+                          << ND->getDeclName());
 }
 
 void Sema::CheckArrayAccess(const Expr *expr) {
   while (true) {
     expr = expr->IgnoreParens();
     switch (expr->getStmtClass()) {
-      case Stmt::ArraySubscriptExprClass:
-        CheckArrayAccess_Check(*this, cast<ArraySubscriptExpr>(expr));
+      case Stmt::ArraySubscriptExprClass: {
+        const ArraySubscriptExpr *ASE = cast<ArraySubscriptExpr>(expr);
+        CheckArrayAccess(ASE->getBase(),
+                         ASE->getIdx(), true);
         return;
+      }
       case Stmt::ConditionalOperatorClass: {
         const ConditionalOperator *cond = cast<ConditionalOperator>(expr);
         if (const Expr *lhs = cond->getLHS())