[PATCH] Make ScalarEvolution less aggressive with respect to no-wrap flags.

[Andrew Trick]

LGTM with one suggestion for comment.
Thanks for the test cases.


================
Comment at: lib/Analysis/ScalarEvolution.cpp:3464-3469
@@ -3463,8 +3464,2 @@
                 }
-              } else if (const SubOperator *OBO =
-                           dyn_cast<SubOperator>(BEValueV)) {
-                if (OBO->hasNoUnsignedWrap())
-                  Flags = setFlags(Flags, SCEV::FlagNUW);
-                if (OBO->hasNoSignedWrap())
-                  Flags = setFlags(Flags, SCEV::FlagNSW);
               }
----------------
Add a short comment that subtract does not preserve nsw/nuw Flags.

http://reviews.llvm.org/D7081

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