Index: cfe/trunk/lib/Driver/ToolChains/Clang.cpp
===================================================================
--- cfe/trunk/lib/Driver/ToolChains/Clang.cpp
+++ cfe/trunk/lib/Driver/ToolChains/Clang.cpp
@@ -3545,6 +3545,18 @@
   // Select the appropriate action.
   RewriteKind rewriteKind = RK_None;
 
+  // If CollectArgsForIntegratedAssembler() isn't called below, call it here
+  // with a dummy args list to mark assembler flags as used even when not
+  // running an assembler. Otherwise, clang would emit "argument unused"
+  // warnings for assembler flags when e.g. adding "-E" to flags while debugging
+  // something. That'd be somewhat inconvenient, and it's also inconsistent with
+  // most other flags -- we don't warn on -ffunction-sections not being used
+  // in -E mode either for example, even though it's not really used either.
+  if (!isa<AssembleJobAction>(JA)) {
+    ArgStringList DummyArgs;
+    CollectArgsForIntegratedAssembler(C, Args, DummyArgs, D);
+  }
+
   if (isa<AnalyzeJobAction>(JA)) {
     assert(JA.getType() == types::TY_Plist && "Invalid output type.");
     CmdArgs.push_back("-analyze");
Index: cfe/trunk/test/Driver/as-options.s
===================================================================
--- cfe/trunk/test/Driver/as-options.s
+++ cfe/trunk/test/Driver/as-options.s
@@ -35,3 +35,14 @@
 // RUN:   | FileCheck %s
 
 // CHECK: "-I" "foo_dir"
+
+// Test that assembler options don't cause warnings when there's no assembler
+// stage.
+
+// RUN: %clang -mincremental-linker-compatible -E -o /dev/null %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=WARN --allow-empty %s
+// RUN: %clang -mimplicit-it=always -target armv7-linux-gnueabihf -E %s \
+// RUN:   | FileCheck --check-prefix=WARN --allow-empty %s
+// RUN: %clang -Wa,-mbig-obj -target i386-pc-windows -E %s \
+// RUN:   | FileCheck --check-prefix=WARN --allow-empty %s
+// WARN-NOT: unused