diff --git a/clang-tools-extra/clangd/CompileCommands.cpp b/clang-tools-extra/clangd/CompileCommands.cpp
--- a/clang-tools-extra/clangd/CompileCommands.cpp
+++ b/clang-tools-extra/clangd/CompileCommands.cpp
@@ -423,6 +423,8 @@
   if (!Opt.hasFlag(driver::options::NoDriverOption)) {
     if (Opt.hasFlag(driver::options::CLOption)) {
       Result |= DM_CL;
+    } else if (Opt.hasFlag(driver::options::CLDXCOption)) {
+      Result |= DM_CL;
     } else {
       Result |= DM_GCC;
       if (Opt.hasFlag(driver::options::CoreOption)) {
diff --git a/clang/include/clang/Driver/Options.h b/clang/include/clang/Driver/Options.h
--- a/clang/include/clang/Driver/Options.h
+++ b/clang/include/clang/Driver/Options.h
@@ -36,7 +36,8 @@
   FC1Option = (1 << 15),
   FlangOnlyOption = (1 << 16),
   DXCOption = (1 << 17),
-  Ignored = (1 << 18),
+  CLDXCOption = (1 << 18),
+  Ignored = (1 << 19),
 };
 
 enum ID {
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -53,6 +53,10 @@
 // are made available when the driver is running in DXC compatibility mode.
 def DXCOption : OptionFlag;
 
+// CLDXCOption - This is a cl.exe/dxc.exe compatibility option. Options with this flag
+// are made available when the driver is running in CL/DXC compatibility mode.
+def CLDXCOption : OptionFlag;
+
 // NoDriverOption - This option should not be accepted by the driver.
 def NoDriverOption : OptionFlag;
 
@@ -6355,7 +6359,7 @@
 // clang-cl Options
 //===----------------------------------------------------------------------===//
 
-def cl_Group : OptionGroup<"<clang-cl options>">, Flags<[CLOption]>,
+def cl_Group : OptionGroup<"<clang-cl options>">, Flags<[CLDXCOption]>,
   HelpText<"CL.EXE COMPATIBILITY OPTIONS">;
 
 def cl_compile_Group : OptionGroup<"<clang-cl compile-only options>">,
@@ -6385,6 +6389,9 @@
 class CLJoinedOrSeparate<string name> : Option<["/", "-"], name,
   KIND_JOINED_OR_SEPARATE>, Group<cl_Group>, Flags<[CLOption, NoXarchOption]>;
 
+class CLDXCJoinedOrSeparate<string name> : Option<["/", "-"], name,
+  KIND_JOINED_OR_SEPARATE>, Group<cl_Group>, Flags<[CLDXCOption, NoXarchOption]>;
+
 class CLCompileJoinedOrSeparate<string name> : Option<["/", "-"], name,
   KIND_JOINED_OR_SEPARATE>, Group<cl_compile_Group>,
   Flags<[CLOption, NoXarchOption]>;
@@ -6462,7 +6469,7 @@
 def _SLASH_HELP : CLFlag<"HELP">, Alias<help>;
 def _SLASH_hotpatch : CLFlag<"hotpatch">, Alias<fms_hotpatch>,
   HelpText<"Create hotpatchable image">;
-def _SLASH_I : CLJoinedOrSeparate<"I">,
+def _SLASH_I : CLDXCJoinedOrSeparate<"I">,
   HelpText<"Add directory to include search path">, MetaVarName<"<dir>">,
   Alias<I>;
 def _SLASH_J : CLFlag<"J">, HelpText<"Make char type unsigned">,
diff --git a/clang/lib/Driver/Driver.cpp b/clang/lib/Driver/Driver.cpp
--- a/clang/lib/Driver/Driver.cpp
+++ b/clang/lib/Driver/Driver.cpp
@@ -6262,6 +6262,7 @@
   if (IsClCompatMode) {
     // Include CL and Core options.
     IncludedFlagsBitmask |= options::CLOption;
+    IncludedFlagsBitmask |= options::CLDXCOption;
     IncludedFlagsBitmask |= options::CoreOption;
   } else {
     ExcludedFlagsBitmask |= options::CLOption;
@@ -6269,10 +6270,14 @@
   if (IsDXCMode()) {
     // Include DXC and Core options.
     IncludedFlagsBitmask |= options::DXCOption;
+    IncludedFlagsBitmask |= options::CLDXCOption;
     IncludedFlagsBitmask |= options::CoreOption;
   } else {
     ExcludedFlagsBitmask |= options::DXCOption;
   }
+  if (!IsClCompatMode && !IsDXCMode())
+    ExcludedFlagsBitmask |= options::CLDXCOption;
+
   return std::make_pair(IncludedFlagsBitmask, ExcludedFlagsBitmask);
 }
 
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -3511,6 +3511,7 @@
                               types::ID InputType) {
   const unsigned ForwardedArguments[] = {options::OPT_dxil_validator_version,
                                          options::OPT_D,
+                                         options::OPT_I,
                                          options::OPT_S,
                                          options::OPT_emit_llvm,
                                          options::OPT_disable_llvm_passes,
diff --git a/clang/test/Driver/dxc_I.hlsl b/clang/test/Driver/dxc_I.hlsl
new file mode 100644
--- /dev/null
+++ b/clang/test/Driver/dxc_I.hlsl
@@ -0,0 +1,4 @@
+// RUN: %clang_dxc -I test  -### %s 2>&1 | FileCheck %s
+
+// Make sure -I send to cc1.
+// CHECK:"-I" "test"