diff --git a/clang/include/clang/Basic/Builtins.h b/clang/include/clang/Basic/Builtins.h
--- a/clang/include/clang/Basic/Builtins.h
+++ b/clang/include/clang/Basic/Builtins.h
@@ -42,6 +42,7 @@
   OCL_PIPE = 0x200,          // builtin requires OpenCL pipe.
   OCL_DSE = 0x400,           // builtin requires OpenCL device side enqueue.
   ALL_OCL_LANGUAGES = 0x800, // builtin for OCL languages.
+  HLSL_LANG = 0x1000,        // builtin requires HLSL.
   ALL_LANGUAGES = C_LANG | CXX_LANG | OBJC_LANG, // builtin for all languages.
   ALL_GNU_LANGUAGES = ALL_LANGUAGES | GNU_LANG,  // builtin requires GNU mode.
   ALL_MS_LANGUAGES = ALL_LANGUAGES | MS_LANG     // builtin requires MS mode.
diff --git a/clang/include/clang/Basic/Builtins.def b/clang/include/clang/Basic/Builtins.def
--- a/clang/include/clang/Basic/Builtins.def
+++ b/clang/include/clang/Basic/Builtins.def
@@ -1693,6 +1693,9 @@
 // CUDA/HIP
 LANGBUILTIN(__builtin_get_device_side_mangled_name, "cC*.", "ncT", CUDA_LANG)
 
+// HLSL
+LANGBUILTIN(WaveActiveCountBits, "Uib", "nc", HLSL_LANG)
+
 // Builtins for XRay
 BUILTIN(__xray_customevent, "vcC*z", "")
 BUILTIN(__xray_typedevent, "vzcC*z", "")
diff --git a/clang/test/SemaHLSL/Wave.hlsl b/clang/test/SemaHLSL/Wave.hlsl
new file mode 100644
--- /dev/null
+++ b/clang/test/SemaHLSL/Wave.hlsl
@@ -0,0 +1,8 @@
+// RUN: %clang_cc1  -x hlsl -triple dxil--shadermodel6.7-library  %s  -verify
+
+// Make sure WaveActiveCountBits is accepted.
+
+// expected-no-diagnostics
+unsigned foo(bool b) {
+    return WaveActiveCountBits(b);
+}