diff --git a/clang/include/clang/Basic/Attr.td b/clang/include/clang/Basic/Attr.td
--- a/clang/include/clang/Basic/Attr.td
+++ b/clang/include/clang/Basic/Attr.td
@@ -908,6 +908,7 @@
              .Case("maccatalyst", "macCatalyst")
              .Case("maccatalyst_app_extension", "macCatalyst (App Extension)")
              .Case("swift", "Swift")
+             .Case("shadermodel", "HLSL ShaderModel")
              .Default(llvm::StringRef());
 }
 static llvm::StringRef getPlatformNameSourceSpelling(llvm::StringRef Platform) {
@@ -923,6 +924,7 @@
              .Case("maccatalyst", "macCatalyst")
              .Case("maccatalyst_app_extension", "macCatalystApplicationExtension")
              .Case("zos", "z/OS")
+             .Case("shadermodel", "ShaderModel")
              .Default(Platform);
 }
 static llvm::StringRef canonicalizePlatformName(llvm::StringRef Platform) {
@@ -937,6 +939,7 @@
              .Case("watchOSApplicationExtension", "watchos_app_extension")
              .Case("macCatalyst", "maccatalyst")
              .Case("macCatalystApplicationExtension", "maccatalyst_app_extension")
+             .Case("ShaderModel", "shadermodel")
              .Default(Platform);
 } }];
   let HasCustomParsing = 1;
diff --git a/clang/lib/Basic/Targets/DirectX.h b/clang/lib/Basic/Targets/DirectX.h
--- a/clang/lib/Basic/Targets/DirectX.h
+++ b/clang/lib/Basic/Targets/DirectX.h
@@ -55,6 +55,8 @@
     HasLegalHalfType = true;
     HasFloat16 = true;
     NoAsmVariants = true;
+    PlatformMinVersion = Triple.getOSVersion();
+    PlatformName = llvm::Triple::getOSTypeName(Triple.getOS());
     resetDataLayout("e-m:e-p:32:32-i1:32-i8:8-i16:16-i32:32-i64:64-f16:16-f32:"
                     "32-f64:64-n8:16:32:64");
     TheCXXABI.set(TargetCXXABI::Microsoft);
diff --git a/clang/lib/Headers/hlsl/hlsl_intrinsics.h b/clang/lib/Headers/hlsl/hlsl_intrinsics.h
--- a/clang/lib/Headers/hlsl/hlsl_intrinsics.h
+++ b/clang/lib/Headers/hlsl/hlsl_intrinsics.h
@@ -9,6 +9,7 @@
 #ifndef _HLSL_HLSL_INTRINSICS_H_
 #define _HLSL_HLSL_INTRINSICS_H_
 
+__attribute__((availability(shadermodel, introduced = 6.0)))
 __attribute__((clang_builtin_alias(__builtin_hlsl_wave_active_count_bits))) uint
 WaveActiveCountBits(bool bBit);
 
diff --git a/clang/lib/Sema/SemaAvailability.cpp b/clang/lib/Sema/SemaAvailability.cpp
--- a/clang/lib/Sema/SemaAvailability.cpp
+++ b/clang/lib/Sema/SemaAvailability.cpp
@@ -192,6 +192,9 @@
   case llvm::Triple::MacOSX:
     ForceAvailabilityFromVersion = VersionTuple(/*Major=*/10, /*Minor=*/13);
     break;
+  case llvm::Triple::ShaderModel:
+    // Always enable availability diagnostics for shader models.
+    return true;
   default:
     // New targets should always warn about availability.
     return Triple.getVendor() == llvm::Triple::Apple;
diff --git a/clang/test/SemaHLSL/AvailabilityMarkup.hlsl b/clang/test/SemaHLSL/AvailabilityMarkup.hlsl
new file mode 100644
--- /dev/null
+++ b/clang/test/SemaHLSL/AvailabilityMarkup.hlsl
@@ -0,0 +1,25 @@
+// RUN: %clang_cc1 -triple dxil-pc-shadermodel5.0-library -verify %s
+
+__attribute__((availability(shadermodel, introduced = 6.0)))
+unsigned fn6_0(); // #fn6_0
+
+__attribute__((availability(shadermodel, introduced = 5.1)))
+unsigned fn5_1(); // #fn5_1
+
+__attribute__((availability(shadermodel, introduced = 5.0)))
+unsigned fn5_0();
+
+void fn() {
+    // expected-warning@#fn6_0_site {{'fn6_0' is only available on HLSL ShaderModel 6.0 or newer}}
+    // expected-note@#fn6_0 {{'fn6_0' has been marked as being introduced in HLSL ShaderModel 6.0 here, but the deployment target is HLSL ShaderModel 5.0}}
+    // expected-note@#fn6_0_site {{enclose 'fn6_0' in a __builtin_available check to silence this warning}}
+    unsigned A = fn6_0(); // #fn6_0_site
+
+    // expected-warning@#fn5_1_site {{'fn5_1' is only available on HLSL ShaderModel 5.1 or newer}}
+    // expected-note@#fn5_1 {{'fn5_1' has been marked as being introduced in HLSL ShaderModel 5.1 here, but the deployment target is HLSL ShaderModel 5.0}}
+    // expected-note@#fn5_1_site {{enclose 'fn5_1' in a __builtin_available check to silence this warning}}
+    unsigned B = fn5_1(); // #fn5_1_site
+
+    unsigned C = fn5_0();
+}
+
diff --git a/clang/test/SemaHLSL/WaveBuiltinAvailability.hlsl b/clang/test/SemaHLSL/WaveBuiltinAvailability.hlsl
new file mode 100644
--- /dev/null
+++ b/clang/test/SemaHLSL/WaveBuiltinAvailability.hlsl
@@ -0,0 +1,9 @@
+// RUN: %clang_cc1 -finclude-default-header -triple dxil-pc-shadermodel5.0-library -verify %s
+// WaveActiveCountBits is unavailable before ShaderModel 6.0.
+
+unsigned foo(bool b) {
+    // expected-warning@#site {{'WaveActiveCountBits' is only available on HLSL ShaderModel 6.0 or newer}}
+    // expected-note@hlsl/hlsl_intrinsics.h:* {{'WaveActiveCountBits' has been marked as being introduced in HLSL ShaderModel 6.0 here, but the deployment target is HLSL ShaderModel 5.0}}
+    // expected-note@#site {{enclose 'WaveActiveCountBits' in a __builtin_available check to silence this warning}}
+    return WaveActiveCountBits(b); // #site
+}