Index: cfe/trunk/lib/Driver/ToolChains/Clang.cpp
===================================================================
--- cfe/trunk/lib/Driver/ToolChains/Clang.cpp
+++ cfe/trunk/lib/Driver/ToolChains/Clang.cpp
@@ -4873,7 +4873,9 @@
 
   // Both /showIncludes and /E (and /EP) write to stdout. Allowing both
   // would produce interleaved output, so ignore /showIncludes in such cases.
-  if (!Args.hasArg(options::OPT_E) && !Args.hasArg(options::OPT__SLASH_EP))
+  if ((!Args.hasArg(options::OPT_E) && !Args.hasArg(options::OPT__SLASH_EP)) ||
+      (Args.hasArg(options::OPT__SLASH_P) &&
+       Args.hasArg(options::OPT__SLASH_EP) && !Args.hasArg(options::OPT_E)))
     if (Arg *A = Args.getLastArg(options::OPT_show_includes))
       A->render(Args, CmdArgs);
 
Index: cfe/trunk/test/Driver/cl-options.c
===================================================================
--- cfe/trunk/test/Driver/cl-options.c
+++ cfe/trunk/test/Driver/cl-options.c
@@ -197,8 +197,12 @@
 
 // RUN: %clang_cl /E /showIncludes -### -- %s 2>&1 | FileCheck -check-prefix=showIncludes_E %s
 // RUN: %clang_cl /EP /showIncludes -### -- %s 2>&1 | FileCheck -check-prefix=showIncludes_E %s
+// RUN: %clang_cl /E /EP /showIncludes -### -- %s 2>&1 | FileCheck -check-prefix=showIncludes_E %s
 // showIncludes_E: warning: argument unused during compilation: '--show-includes'
 
+// RUN: %clang_cl /EP /P /showIncludes -### -- %s 2>&1 | FileCheck -check-prefix=showIncludes_E_And_P %s
+// showIncludes_E_And_P-NOT: warning: argument unused during compilation: '--show-includes'
+
 // /source-charset: should warn on everything except UTF-8.
 // RUN: %clang_cl /source-charset:utf-16 -### -- %s 2>&1 | FileCheck -check-prefix=source-charset-utf-16 %s
 // source-charset-utf-16: invalid value 'utf-16'