Teach isKnownNonNull that a nonnull return is not null. Add a test for this case as well as the case of a nonnull attribute (already handled but not tested).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209193 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Analysis/ValueTracking.cpp

@@ -16,6 +16,7 @@
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/Analysis/InstructionSimplify.h"
 #include "llvm/Analysis/MemoryBuiltins.h"
+#include "llvm/IR/CallSite.h"
 #include "llvm/IR/ConstantRange.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/DataLayout.h"
@@ -2073,6 +2074,10 @@ bool llvm::isKnownNonNull(const Value *V, const TargetLibraryInfo *TLI) {
   if (const GlobalValue *GV = dyn_cast<GlobalValue>(V))
     return !GV->hasExternalWeakLinkage();
 
+  if (ImmutableCallSite CS = V)
+    if (CS.paramHasAttr(0, Attribute::NonNull))
+      return true;
+
   // operator new never returns null.
   if (isOperatorNewLikeFn(V, TLI, /*LookThroughBitCast=*/true))
     return true;