fix a fixme by improving const correctness.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@45633 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/utils/TableGen/CodeGenDAGPatterns.h b/utils/TableGen/CodeGenDAGPatterns.h
index 6a1be8c..d386963 100644
--- a/utils/TableGen/CodeGenDAGPatterns.h
+++ b/utils/TableGen/CodeGenDAGPatterns.h
@@ -507,10 +507,9 @@
   pf_iterator pf_end() const { return PatternFragments.end(); }
 
   // Patterns to match information.
-  // FIXME: make a const_iterator.
-  typedef std::vector<PatternToMatch>::iterator ptm_iterator;
-  ptm_iterator ptm_begin() { return PatternsToMatch.begin(); }
-  ptm_iterator ptm_end() { return PatternsToMatch.end(); }
+  typedef std::vector<PatternToMatch>::const_iterator ptm_iterator;
+  ptm_iterator ptm_begin() const { return PatternsToMatch.begin(); }
+  ptm_iterator ptm_end() const { return PatternsToMatch.end(); }