Let llvm.objectsize be conservative with null pointers

D28494 adds another parameter to @llvm.objectsize. Clang needs to be
sure to pass that third arg whenever applicable.

llvm-svn: 298431
diff --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
index 1118bfa..1a95eb1 100644
--- a/clang/lib/CodeGen/CGExpr.cpp
+++ b/clang/lib/CodeGen/CGExpr.cpp
@@ -581,10 +581,11 @@
     llvm::Type *Tys[2] = { IntPtrTy, Int8PtrTy };
     llvm::Value *F = CGM.getIntrinsic(llvm::Intrinsic::objectsize, Tys);
     llvm::Value *Min = Builder.getFalse();
+    llvm::Value *NullIsUnknown = Builder.getFalse();
     llvm::Value *CastAddr = Builder.CreateBitCast(Ptr, Int8PtrTy);
-    llvm::Value *LargeEnough =
-        Builder.CreateICmpUGE(Builder.CreateCall(F, {CastAddr, Min}),
-                              llvm::ConstantInt::get(IntPtrTy, Size));
+    llvm::Value *LargeEnough = Builder.CreateICmpUGE(
+        Builder.CreateCall(F, {CastAddr, Min, NullIsUnknown}),
+        llvm::ConstantInt::get(IntPtrTy, Size));
     Checks.push_back(std::make_pair(LargeEnough, SanitizerKind::ObjectSize));
   }