Rename isKnownNotFullPoison to programUndefinedIfPoison; NFC

Summary:
programUndefinedIfPoison makes more sense, given what the function
does; and I'm about to add a function with a name similar to
isKnownNotFullPoison (so do the rename to avoid confusion).

Reviewers: broune, majnemer, bjarke.roune

Reviewed By: broune

Subscribers: mcrosier, llvm-commits, mzolotukhin

Differential Revision: https://reviews.llvm.org/D30444

llvm-svn: 301776
diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 1aadac4..bd747f7 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -5029,7 +5029,8 @@
     return false;
 
   // Only proceed if we can prove that I does not yield poison.
-  if (!isKnownNotFullPoison(I)) return false;
+  if (!programUndefinedIfFullPoison(I))
+    return false;
 
   // At this point we know that if I is executed, then it does not wrap
   // according to at least one of NSW or NUW. If I is not executed, then we do