[llvm] Add isa_and_nonnull

Summary:
Add new ``isa_and_nonnull<>`` operator that works just like
the ``isa<>`` operator, except that it allows for a null pointer as an
argument (which it then returns false).

Reviewers: lattner, aaron.ballman, greened

Reviewed By: lattner

Subscribers: hubert.reinterpretcast, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D60291

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@357761 91177308-0d34-0410-b5e6-96231b3b80d8

docs/ProgrammersManual.rst

@@ -164,6 +164,12 @@ rarely have to include this file directly).
   efficient to use the ``InstVisitor`` class to dispatch over the instruction
   type directly.
 
+``isa_and_nonnull<>``:
+  The ``isa_and_nonnull<>`` operator works just like the ``isa<>`` operator,
+  except that it allows for a null pointer as an argument (which it then
+  returns false).  This can sometimes be useful, allowing you to combine several
+  null checks into one.
+
 ``cast_or_null<>``:
   The ``cast_or_null<>`` operator works just like the ``cast<>`` operator,
   except that it allows for a null pointer as an argument (which it then

include/llvm/Support/Casting.h

@@ -143,6 +143,16 @@ template <class X, class Y> LLVM_NODISCARD inline bool isa(const Y &Val) {
                        typename simplify_type<const Y>::SimpleType>::doit(Val);
 }
 
+// isa_and_nonnull<X> - Functionally identical to isa, except that a null value
+// is accepted.
+//
+template <class X, class Y>
+LLVM_NODISCARD inline bool isa_and_nonnull(const Y &Val) {
+  if (!Val)
+    return false;
+  return isa<X>(Val);
+}
+
 //===----------------------------------------------------------------------===//
 //                          cast<x> Support Templates
 //===----------------------------------------------------------------------===//

unittests/Support/Casting.cpp

@@ -118,6 +118,12 @@ TEST(CastingTest, isa) {
   EXPECT_TRUE(isa<foo>(B4));
 }
 
+TEST(CastingTest, isa_and_nonnull) {
+  EXPECT_TRUE(isa_and_nonnull<foo>(B2));
+  EXPECT_TRUE(isa_and_nonnull<foo>(B4));
+  EXPECT_FALSE(isa_and_nonnull<foo>(fub()));
+}
+
 TEST(CastingTest, cast) {
   foo &F1 = cast<foo>(B1);
   EXPECT_NE(&F1, null_foo);