Spell `necessary' correctly.

llvm-svn: 7944
diff --git a/llvm/lib/CodeGen/RegAllocSimple.cpp b/llvm/lib/CodeGen/RegAllocSimple.cpp
index ba571e4..57d678b 100644
--- a/llvm/lib/CodeGen/RegAllocSimple.cpp
+++ b/llvm/lib/CodeGen/RegAllocSimple.cpp
@@ -58,7 +58,7 @@
     void AllocateBasicBlock(MachineBasicBlock &MBB);
 
     /// getStackSpaceFor - This returns the offset of the specified virtual
-    /// register on the stack, allocating space if neccesary.
+    /// register on the stack, allocating space if necessary.
     int getStackSpaceFor(unsigned VirtReg, const TargetRegisterClass *RC);
 
     /// Given a virtual register, return a compatible physical register that is