Index: clang/lib/Driver/ToolChains/Clang.cpp
===================================================================
--- clang/lib/Driver/ToolChains/Clang.cpp
+++ clang/lib/Driver/ToolChains/Clang.cpp
@@ -2079,6 +2079,9 @@
     break;
   }
 
+  // If you add more args here, also add them to the block below that
+  // starts with "// If CollectArgsForIntegratedAssembler() isn't called below".
+
   // When passing -I arguments to the assembler we sometimes need to
   // unconditionally take the next argument.  For example, when parsing
   // '-Wa,-I -Wa,foo' we need to accept the -Wa,foo arg after seeing the
@@ -3543,6 +3546,35 @@
   // Select the appropriate action.
   RewriteKind rewriteKind = RK_None;
 
+  // If CollectArgsForIntegratedAssembler() isn't called below, claim the args
+  // it claims 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)) {
+    // The args claimed here should match the args used in
+    // CollectArgsForIntegratedAssembler().
+    if (TC.useIntegratedAs()) {
+      Args.ClaimAllArgs(options::OPT_mrelax_all);
+      Args.ClaimAllArgs(options::OPT_mno_relax_all);
+      Args.ClaimAllArgs(options::OPT_mincremental_linker_compatible);
+      Args.ClaimAllArgs(options::OPT_mno_incremental_linker_compatible);
+      switch (C.getDefaultToolChain().getArch()) {
+      case llvm::Triple::arm:
+      case llvm::Triple::armeb:
+      case llvm::Triple::thumb:
+      case llvm::Triple::thumbeb:
+        Args.ClaimAllArgs(options::OPT_mimplicit_it_EQ);
+      default:
+        break;
+      }
+    }
+    Args.ClaimAllArgs(options::OPT_Wa_COMMA);
+    Args.ClaimAllArgs(options::OPT_Xassembler);
+  }
+
   if (isa<AnalyzeJobAction>(JA)) {
     assert(JA.getType() == types::TY_Plist && "Invalid output type.");
     CmdArgs.push_back("-analyze");
Index: clang/test/Driver/as-options.s
===================================================================
--- clang/test/Driver/as-options.s
+++ clang/test/Driver/as-options.s
@@ -35,3 +35,51 @@
 // 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 \
+// RUN:   -o /dev/null -x c++ %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=NOWARN --allow-empty %s
+// RUN: %clang -mincremental-linker-compatible -E \
+// RUN:   -o /dev/null -x assembler-with-cpp %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=NOWARN --allow-empty %s
+// RUN: %clang -mimplicit-it=always -target armv7-linux-gnueabi -E \
+// RUN:   -o /dev/null -x c++ %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=NOWARN --allow-empty %s
+// RUN: %clang -mimplicit-it=always -target armv7-linux-gnueabi -E \
+// RUN:   -o /dev/null -x assembler-with-cpp %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=NOWARN --allow-empty %s
+// RUN: %clang -Wa,-mbig-obj -target i386-pc-windows -E \
+// RUN:   -o /dev/null -x c++ %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=NOWARN --allow-empty %s
+// RUN: %clang -Wa,-mbig-obj -target i386-pc-windows -E \
+// RUN:   -o /dev/null -x assembler-with-cpp %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=NOWARN --allow-empty %s
+// RUN: %clang -Xassembler -mbig-obj -target i386-pc-windows -E \
+// RUN:   -o /dev/null -x c++ %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=NOWARN --allow-empty %s
+// RUN: %clang -Xassembler -mbig-obj -target i386-pc-windows -E \
+// RUN:   -o /dev/null -x assembler-with-cpp %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=NOWARN --allow-empty %s
+// NOWARN-NOT: unused
+
+// Test that unsupported arguments do not cause errors when -fno-integrated-as
+// is set.
+// RUN: %clang -Wa,-mno-warn-deprecated -fno-integrated-as %s -S 2>&1 \
+// RUN:   | FileCheck --check-prefix=NOERROR --allow-empty %s
+// NOERROR-NOT: error: unsupported argument '-mno-warn-deprecated' to option 'Wa,'
+
+// -Wa flags shouldn't cause warnings without an assembler stage with
+// -fno-integrated-as either.
+// RUN: %clang -Wa,-mno-warn-deprecated -fno-integrated-as %s -S 2>&1 \
+// RUN:   | FileCheck --check-prefix=NOWARN --allow-empty %s
+
+// But -m flags for the integrated assembler _should_ warn if the integrated
+// assembler is not in use.
+// RUN: %clang -mrelax-all -fintegrated-as %s -S 2>&1 \
+// RUN:   | FileCheck --check-prefix=NOWARN --allow-empty %s
+// RUN: %clang -mrelax-all -fno-integrated-as %s -S 2>&1 \
+// RUN:   | FileCheck --check-prefix=WARN --allow-empty %s
+// WARN: unused