[PeepholeOptimzer] Fix a typo in a comment.
Spotted by Amara Emerson.

llvm-svn: 212106
diff --git a/llvm/lib/CodeGen/PeepholeOptimizer.cpp b/llvm/lib/CodeGen/PeepholeOptimizer.cpp
index 6f37518..716cb1f 100644
--- a/llvm/lib/CodeGen/PeepholeOptimizer.cpp
+++ b/llvm/lib/CodeGen/PeepholeOptimizer.cpp
@@ -844,7 +844,7 @@
     // Def.sub1 =
     // is a valid SSA representation for Def.sub0 and Def.sub1, but not for
     // Def. Thus, it must not be generated.
-    // However, some code could theoritically generates a single
+    // However, some code could theoretically generates a single
     // Def.sub0 (i.e, not defining the other subregs) and we would
     // have this case.
     // If we can ascertain (or force) that this never happens, we could