uint32 : HandlerPCOffset
}
}
+
+
+The ``ImplicitNullChecks`` pass
+===============================
+
+The ``ImplicitNullChecks`` pass transforms explicit control flow for
+checking if a pointer is ``null``, like:
+
+.. code-block:: llvm
+
+ %ptr = call i32* @get_ptr()
+ %ptr_is_null = icmp i32* %ptr, null
+ br i1 %ptr_is_null, label %is_null, label %not_null
+
+ not_null:
+ %t = load i32, i32* %ptr
+ br label %do_something_with_t
+
+ is_null:
+ call void @HFC()
+ unreachable
+
+to control flow implicit in the instruction loading or storing through
+the pointer being null checked:
+
+.. code-block:: llvm
+
+ %ptr = call i32* @get_ptr()
+ %t = load i32, i32* %ptr ;; handler-pc = label %is_null
+ br label %do_something_with_t
+
+ is_null:
+ call void @HFC()
+ unreachable
+
+This transform happens at the ``MachineInstr`` level, not the LLVM IR
+level (so the above example is only representative, not literal). The
+``ImplicitNullChecks`` pass runs during codegen, if
+``-enable-implicit-null-checks`` is passed to ``llc``.
+
+The ``ImplicitNullChecks`` pass adds entries to the
+``__llvm_faultmaps`` section described above as needed.