diff --git a/clang/include/clang/AST/Attr.h b/clang/include/clang/AST/Attr.h
--- a/clang/include/clang/AST/Attr.h
+++ b/clang/include/clang/AST/Attr.h
@@ -190,6 +190,22 @@
   }
 };
 
+class HLSLAnnotationAttr : public InheritableAttr {
+protected:
+  HLSLAnnotationAttr(ASTContext &Context, const AttributeCommonInfo &CommonInfo,
+                     attr::Kind AK, bool IsLateParsed,
+                     bool InheritEvenIfAlreadyPresent)
+      : InheritableAttr(Context, CommonInfo, AK, IsLateParsed,
+                        InheritEvenIfAlreadyPresent) {}
+
+public:
+  // Implement isa/cast/dyncast/etc.
+  static bool classof(const Attr *A) {
+    return A->getKind() >= attr::FirstHLSLAnnotationAttr &&
+           A->getKind() <= attr::LastHLSLAnnotationAttr;
+  }
+};
+
 /// A parameter attribute which changes the argument-passing ABI rule
 /// for the parameter.
 class ParameterABIAttr : public InheritableParamAttr {
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
@@ -607,6 +607,9 @@
 /// A attribute is either a declaration attribute or a statement attribute.
 class DeclOrStmtAttr : InheritableAttr;
 
+/// An attribute class for HLSL Annotations.
+class HLSLAnnotationAttr : InheritableAttr;
+
 /// A target-specific attribute.  This class is meant to be used as a mixin
 /// with InheritableAttr or Attr depending on the attribute's needs.
 class TargetSpecificAttr<TargetSpec target> {
@@ -4005,7 +4008,7 @@
   let Documentation = [NumThreadsDocs];
 }
 
-def HLSLSV_GroupIndex: InheritableAttr {
+def HLSLSV_GroupIndex: HLSLAnnotationAttr {
   let Spellings = [HLSLSemantic<"SV_GroupIndex">];
   let Subjects = SubjectList<[ParmVar, GlobalVar]>;
   let LangOpts = [HLSL];
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -11632,6 +11632,7 @@
 def err_hlsl_numthreads_invalid : Error<"total number of threads cannot exceed %0">;
 def err_hlsl_missing_numthreads : Error<"missing numthreads attribute for %0 shader entry">;
 def err_hlsl_attribute_param_mismatch : Error<"%0 attribute parameters do not match the previous declaration">;
+def err_hlsl_missing_semantic_annotation : Error<"semantic annotations must be present for all parameters of an entry function or patch constant function">;
 
 def err_hlsl_pointers_unsupported : Error<
   "%select{pointers|references}0 are unsupported in HLSL">;
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -11870,6 +11870,15 @@
     }
     break;
   }
+
+  for (const auto *Param : FD->parameters()) {
+    if (!Param->hasAttr<HLSLAnnotationAttr>()) {
+      // FIXME: Handle struct parameters where annotations are on struct fields.
+      Diag(FD->getLocation(), diag::err_hlsl_missing_semantic_annotation);
+      Diag(Param->getLocation(), diag::note_previous_decl) << Param;
+      FD->setInvalidDecl();
+    }
+  }
 }
 
 bool Sema::CheckForConstantInitializer(Expr *Init, QualType DclT) {
diff --git a/clang/test/SemaHLSL/Semantics/missing_entry_annotation.hlsl b/clang/test/SemaHLSL/Semantics/missing_entry_annotation.hlsl
new file mode 100644
--- /dev/null
+++ b/clang/test/SemaHLSL/Semantics/missing_entry_annotation.hlsl
@@ -0,0 +1,4 @@
+// RUN: %clang_cc1 -triple dxil-pc-shadermodel6.0-compute -x hlsl -fsyntax-only -hlsl-entry main -verify %s
+
+[numthreads(1,1, 1)]
+void main(int GI) { } // expected-error{{semantic annotations must be present for all parameters of an entry function or patch constant function}} expected-note{{'GI' declared here}}
diff --git a/clang/utils/TableGen/ClangAttrEmitter.cpp b/clang/utils/TableGen/ClangAttrEmitter.cpp
--- a/clang/utils/TableGen/ClangAttrEmitter.cpp
+++ b/clang/utils/TableGen/ClangAttrEmitter.cpp
@@ -2852,7 +2852,8 @@
   { "INHERITABLE_ATTR", "InheritableAttr" },
   { "DECL_OR_TYPE_ATTR", "DeclOrTypeAttr" },
   { "INHERITABLE_PARAM_ATTR", "InheritableParamAttr" },
-  { "PARAMETER_ABI_ATTR", "ParameterABIAttr" }
+  { "PARAMETER_ABI_ATTR", "ParameterABIAttr" },
+  { "HLSL_ANNOTATION_ATTR", "HLSLAnnotationAttr"}
 };
 
 static void emitDefaultDefine(raw_ostream &OS, StringRef name,