[Sema] Don't check for array bounds when the types in the base expression are dependent.

[riccibruno]

Summary

Bail-out of CheckArrayAccess when the types of the base expression before and after eventual casts are dependent. We will get another chance to check for array bounds during instantiation. Fixes PR41087.

[efriedma]

LGTM

cfe/trunk/lib/Sema/SemaChecking.cpp

void Sema::CheckArrayAccess(const Expr *BaseExpr, const Expr *IndexExpr,
   BaseExpr = BaseExpr->IgnoreParenCasts();
   const ConstantArrayType *ArrayTy =
       Context.getAsConstantArrayType(BaseExpr->getType());
 
   if (!ArrayTy)
     return;
 
   const Type *BaseType = ArrayTy->getElementType().getTypePtr();
+  if (EffectiveType->isDependentType() || BaseType->isDependentType())
+    return;
 
   Expr::EvalResult Result;
   if (!IndexExpr->EvaluateAsInt(Result, Context, Expr::SE_AllowSideEffects))
     return;
 
   llvm::APSInt index = Result.Val.getInt();
   if (IndexNegated)
     index = -index;

cfe/trunk/test/SemaCXX/array-bounds.cpp

namespace PR39746 {
   class C {};
 
   C &f() { return reinterpret_cast<C *>(xxx)[1]; } // no-warning
   // We have no info on whether this is out-of-bounds.
   C &g() { return reinterpret_cast<C *>(xxx)[2]; } // no-warning
   // We can still diagnose this.
   C &h() { return reinterpret_cast<C *>(xxx)[-1]; } // expected-warning {{array index -1 is before the beginning of the array}}
 }
+
+namespace PR41087 {
+  template <typename Ty> void foo() {
+    Ty buffer[2]; // expected-note 3{{array 'buffer' declared here}}
+    ((char *)buffer)[2] = 'A'; // expected-warning 1{{array index 2 is past the end of the array (which contains 2 elements)}}
+    ((char *)buffer)[-1] = 'A'; // expected-warning 2{{array index -1 is before the beginning of the array}}
+  }
+
+  void f() {
+    foo<char>(); // expected-note 1{{in instantiation of function template specialization}}
+    foo<int>(); // expected-note 1{{in instantiation of function template specialization}}
+  };
+}