[Sema] Diagnose array access preceding the array bounds even when the base type is incomplete.

When the type of the base expression after IgnoreParenCasts is incomplete,
it is still possible to diagnose an array access which precedes the array
bounds.

This is a follow-up on D55862 which added an early return when the type of
the base expression after IgnoreParenCasts was incomplete.

Differential Revision: https://reviews.llvm.org/D56050

Reviewed By: efriedma

llvm-svn: 350622

1 files changed, 9 insertions, 6 deletions

diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index b9284a5b467..cd96200b817 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -12383,12 +12383,6 @@ void Sema::CheckArrayAccess(const Expr *BaseExpr, const Expr *IndexExpr,
     return;
 
   const Type *BaseType = ArrayTy->getElementType().getTypePtr();
-  // It is possible that the type of the base expression after IgnoreParenCasts
-  // is incomplete, even though the type of the base expression before
-  // IgnoreParenCasts is complete (see PR39746 for an example). In this case we
-  // have no information about whether the array access is out-of-bounds.
-  if (BaseType->isIncompleteType())
-    return;
 
   Expr::EvalResult Result;
   if (!IndexExpr->EvaluateAsInt(Result, Context, Expr::SE_AllowSideEffects))
@@ -12405,6 +12399,15 @@ void Sema::CheckArrayAccess(const Expr *BaseExpr, const Expr *IndexExpr,
     ND = ME->getMemberDecl();
 
   if (index.isUnsigned() || !index.isNegative()) {
+    // It is possible that the type of the base expression after
+    // IgnoreParenCasts is incomplete, even though the type of the base
+    // expression before IgnoreParenCasts is complete (see PR39746 for an
+    // example). In this case we have no information about whether the array
+    // access exceeds the array bounds. However we can still diagnose an array
+    // access which precedes the array bounds.
+    if (BaseType->isIncompleteType())
+      return;
+
     llvm::APInt size = ArrayTy->getSize();
     if (!size.isStrictlyPositive())
       return;