diff --git a/clang/lib/Driver/ToolChains/HLSL.cpp b/clang/lib/Driver/ToolChains/HLSL.cpp
--- a/clang/lib/Driver/ToolChains/HLSL.cpp
+++ b/clang/lib/Driver/ToolChains/HLSL.cpp
@@ -188,5 +188,11 @@
                         Opts.getOption(options::OPT_dxil_validator_version),
                         DefaultValidatorVer);
   }
+  // If entry is not set explicitly, default is main.
+  if (!DAL->hasArg(options::OPT_hlsl_entrypoint)) {
+    const StringRef DefaultEntry = "main";
+    DAL->AddSeparateArg(nullptr, Opts.getOption(options::OPT_hlsl_entrypoint),
+                        DefaultEntry);
+  }
   return DAL;
 }
diff --git a/clang/test/CodeGenHLSL/entry_default.hlsl b/clang/test/CodeGenHLSL/entry_default.hlsl
new file mode 100644
--- /dev/null
+++ b/clang/test/CodeGenHLSL/entry_default.hlsl
@@ -0,0 +1,28 @@
+// RUN: %clang --driver-mode=dxc -Tcs_6_1 -fcgl -Fo - %s | FileCheck %s
+// RUN: %clang --driver-mode=dxc -Efoo -Tcs_6_1 -fcgl -Fo - %s | FileCheck %s --check-prefix=NOTMAIN
+
+// Make sure main is default entry.
+// Make sure not mangle entry.
+// CHECK:define void @main() [[MAIN_ATTR:#[0-9]]]
+// CHECK:define void @_Z3foov() [[FOO_ATTR:#[0-9]]]
+// Make sure only main has dx.shader attribute.
+// CHECK:[[MAIN_ATTR]]
+// CHECK:"dx.shader"="compute"
+// CHECK-SAME:}
+// CHECK:[[FOO_ATTR]]
+// CHECK-NOT:"dx.shader"="compute"
+[numthreads(1, 1, 1)] void main() {
+
+}
+
+// NOTMAIN:define void @main() [[MAIN_ATTR:#[0-9]]]
+// NOTMAIN:define void @foo() [[FOO_ATTR:#[0-9]]]
+// Make sure only foo has dx.shader attribute.
+// NOTMAIN:[[MAIN_ATTR]]
+// NOTMAIN-NOT:"dx.shader"="compute"
+// NOTMAIN-SAME:}
+// NOTMAIN:[[FOO_ATTR]]
+// NOTMAIN-SAME:"dx.shader"="compute"
+[numthreads(1, 1, 1)] void foo() {
+
+}
\ No newline at end of file