diff --git a/clang/lib/AST/Mangle.cpp b/clang/lib/AST/Mangle.cpp
--- a/clang/lib/AST/Mangle.cpp
+++ b/clang/lib/AST/Mangle.cpp
@@ -133,10 +133,6 @@
   if (isa<MSGuidDecl>(D))
     return true;
 
-  // HLSL shader entry function never need to be mangled.
-  if (getASTContext().getLangOpts().HLSL && D->hasAttr<HLSLShaderAttr>())
-    return false;
-
   return shouldMangleCXXName(D);
 }
 
diff --git a/clang/lib/CodeGen/CGHLSLRuntime.h b/clang/lib/CodeGen/CGHLSLRuntime.h
--- a/clang/lib/CodeGen/CGHLSLRuntime.h
+++ b/clang/lib/CodeGen/CGHLSLRuntime.h
@@ -15,6 +15,8 @@
 #ifndef LLVM_CLANG_LIB_CODEGEN_CGHLSLRUNTIME_H
 #define LLVM_CLANG_LIB_CODEGEN_CGHLSLRUNTIME_H
 
+#include "llvm/IR/IRBuilder.h"
+
 #include "clang/Basic/HLSLRuntime.h"
 
 namespace llvm {
@@ -26,6 +28,7 @@
 class CallExpr;
 class Type;
 class VarDecl;
+class ParmVarDecl;
 
 class FunctionDecl;
 
@@ -39,6 +42,8 @@
   uint32_t ResourceCounters[static_cast<uint32_t>(
       hlsl::ResourceClass::NumClasses)] = {0};
 
+  llvm::Value *emitInputSemantic(llvm::IRBuilder<> &B, const ParmVarDecl &D);
+
 public:
   CGHLSLRuntime(CodeGenModule &CGM) : CGM(CGM) {}
   virtual ~CGHLSLRuntime() {}
@@ -48,6 +53,8 @@
   void finishCodeGen();
 
   void setHLSLFunctionAttributes(llvm::Function *, const FunctionDecl *);
+
+  void emitEntryFunction(const FunctionDecl *FD, llvm::Function *Fn);
 };
 
 } // namespace CodeGen
diff --git a/clang/lib/CodeGen/CGHLSLRuntime.cpp b/clang/lib/CodeGen/CGHLSLRuntime.cpp
--- a/clang/lib/CodeGen/CGHLSLRuntime.cpp
+++ b/clang/lib/CodeGen/CGHLSLRuntime.cpp
@@ -14,7 +14,9 @@
 
 #include "CGHLSLRuntime.h"
 #include "CodeGenModule.h"
+#include "clang/AST/Decl.h"
 #include "clang/Basic/TargetOptions.h"
+#include "llvm/IR/IntrinsicsDirectX.h"
 #include "llvm/IR/Metadata.h"
 #include "llvm/IR/Module.h"
 
@@ -95,3 +97,36 @@
                  ShaderAttr->ConvertShaderTypeToStr(ShaderAttr->getType()));
   }
 }
+
+llvm::Value *CGHLSLRuntime::emitInputSemantic(IRBuilder<> &B,
+                                              const ParmVarDecl &D) {
+  assert(D.hasAttrs() && "Entry parameter missing annotation attribute!");
+  if (D.hasAttr<HLSLSV_GroupIndexAttr>()) {
+    llvm::Function *DxGroupIndex =
+        CGM.getIntrinsic(Intrinsic::dx_flattened_thread_id_in_group);
+    CallInst *CI = B.CreateCall(FunctionCallee(DxGroupIndex));
+    return CI;
+  }
+  assert(false && "Unhandled parameter attribute");
+  return nullptr;
+}
+
+void CGHLSLRuntime::emitEntryFunction(const FunctionDecl *FD,
+                                      llvm::Function *Fn) {
+  llvm::Module &M = CGM.getModule();
+  llvm::LLVMContext &Ctx = M.getContext();
+  auto *EntryTy = llvm::FunctionType::get(llvm::Type::getVoidTy(Ctx), false);
+  Function *EntryFn =
+      Function::Create(EntryTy, Function::ExternalLinkage, FD->getName(), &M);
+  BasicBlock *BB = BasicBlock::Create(Ctx, "entry", EntryFn);
+  IRBuilder<> B(BB);
+  llvm::SmallVector<Value *> Args;
+  for (const auto Param : FD->parameters()) {
+    Args.push_back(emitInputSemantic(B, *Param));
+  }
+
+  CallInst *CI = B.CreateCall(FunctionCallee(Fn), Args);
+  (void)CI;
+  // FIXME: Handle codegen for return type semantics
+  B.CreateRetVoid();
+}
diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -16,6 +16,7 @@
 #include "CGCXXABI.h"
 #include "CGCleanup.h"
 #include "CGDebugInfo.h"
+#include "CGHLSLRuntime.h"
 #include "CGOpenMPRuntime.h"
 #include "CodeGenModule.h"
 #include "CodeGenPGO.h"
@@ -907,6 +908,9 @@
   if (D && D->hasAttr<NoProfileFunctionAttr>())
     Fn->addFnAttr(llvm::Attribute::NoProfile);
 
+  if (D && D->hasAttr<HLSLShaderAttr>())
+    CGM.getHLSLRuntime().emitEntryFunction(FD, Fn);
+
   if (D) {
     // Function attributes take precedence over command line flags.
     if (auto *A = D->getAttr<FunctionReturnThunksAttr>()) {
diff --git a/clang/test/CodeGenHLSL/semantics/GroupIndex-codegen.hlsl b/clang/test/CodeGenHLSL/semantics/GroupIndex-codegen.hlsl
new file mode 100644
--- /dev/null
+++ b/clang/test/CodeGenHLSL/semantics/GroupIndex-codegen.hlsl
@@ -0,0 +1,18 @@
+// RUN: %clang_cc1 -triple dxil-pc-shadermodel6.0-compute -x hlsl -emit-llvm -disable-llvm-passes -o - -hlsl-entry main %s
+
+[numthreads(1,1,1)]
+void main(unsigned GI : SV_GroupIndex) {
+  main(GI - 1);
+}
+
+// For HLSL entry functions, we are generating a C-export function that wraps
+// the C++-mangled entry function. The wrapper function can be used to populate
+// semantic parameters and provides the expected void(void) signature that
+// drivers expect for entry points.
+
+//CHECK: define void @main() {
+//CHECK-NEXT: entry:
+//CHECK-NEXT:   %0 = call i32 @llvm.dx.flattened.thread.id.in.group()
+//CHECK-NEXT:   call void @"?main@@YAXI@Z"(i32 %0)
+//CHECK-NEXT:   ret void
+//CHECK-NEXT: }