[InstCombine] Make max size array combine a tunable.

Requested by Sanjoy/Hal a while ago, and forgotten by me
(r283612).

llvm-svn: 294323
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
index 092cc5e..bfa6964 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
+++ b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
@@ -508,6 +508,9 @@
     return llvm::computeOverflowForUnsignedAdd(LHS, RHS, DL, &AC, CxtI, &DT);
   }
 
+  /// Maximum size of array considered when transforming.
+  int MaxArraySizeForCombine;
+
 private:
   /// \brief Performs a few simplifications for operators which are associative
   /// or commutative.