diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index 2d0f05f6ca35b..e32047292ab8a 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -8404,6 +8404,9 @@ def : CLFlag<"O1">, Alias<_SLASH_O>, AliasArgs<["1"]>,
   HelpText<"Optimize for size  (like /Og     /Os /Oy /Ob2 /GF /Gy)">;
 def : CLFlag<"O2">, Alias<_SLASH_O>, AliasArgs<["2"]>,
   HelpText<"Optimize for speed (like /Og /Oi /Ot /Oy /Ob2 /GF /Gy)">;
+def : CLFlag<"O3">, Alias<_SLASH_O>, AliasArgs<["3"]>,
+  HelpText<"Optimize for maximum speed and enable more aggressive optimizations"
+  " that may not improve performance on some programs">;
 def : CLFlag<"Ob0">, Alias<_SLASH_O>, AliasArgs<["b0"]>,
   HelpText<"Disable function inlining">;
 def : CLFlag<"Ob1">, Alias<_SLASH_O>, AliasArgs<["b1"]>,
diff --git a/clang/lib/Driver/ToolChains/MSVC.cpp b/clang/lib/Driver/ToolChains/MSVC.cpp
index c1b912db596e8..52f811621ba82 100644
--- a/clang/lib/Driver/ToolChains/MSVC.cpp
+++ b/clang/lib/Driver/ToolChains/MSVC.cpp
@@ -930,6 +930,7 @@ static void TranslateOptArg(Arg *A, llvm::opt::DerivedArgList &DAL,
       break;
     case '1':
     case '2':
+    case '3':
     case 'x':
     case 'd':
       // Ignore /O[12xd] flags that aren't the last one on the command line.
@@ -946,11 +947,14 @@ static void TranslateOptArg(Arg *A, llvm::opt::DerivedArgList &DAL,
         } else if (OptChar == '2' || OptChar == 'x') {
           DAL.AddFlagArg(A, Opts.getOption(options::OPT_fbuiltin));
           DAL.AddJoinedArg(A, Opts.getOption(options::OPT_O), "2");
+        } else if (OptChar == '3') {
+          DAL.AddFlagArg(A, Opts.getOption(options::OPT_fbuiltin));
+          DAL.AddJoinedArg(A, Opts.getOption(options::OPT_O), "3");
         }
         if (SupportsForcingFramePointer &&
             !DAL.hasArgNoClaim(options::OPT_fno_omit_frame_pointer))
           DAL.AddFlagArg(A, Opts.getOption(options::OPT_fomit_frame_pointer));
-        if (OptChar == '1' || OptChar == '2')
+        if (OptChar == '1' || OptChar == '2' || OptChar == '3')
           DAL.AddFlagArg(A, Opts.getOption(options::OPT_ffunction_sections));
       }
       break;
@@ -1070,7 +1074,8 @@ MSVCToolChain::TranslateArgs(const llvm::opt::DerivedArgList &Args,
         // OptChar does not expand; it's an argument to the previous char.
         continue;
       }
-      if (OptChar == '1' || OptChar == '2' || OptChar == 'x' || OptChar == 'd')
+      if (OptChar == '1' || OptChar == '2' || OptChar == 'x' ||
+          OptChar == 'd' || OptChar == '3')
         ExpandChar = OptStr.data() + I;
     }
   }
diff --git a/clang/test/Driver/Xarch.c b/clang/test/Driver/Xarch.c
index f7693fb689d58..ec58211d6fba0 100644
--- a/clang/test/Driver/Xarch.c
+++ b/clang/test/Driver/Xarch.c
@@ -1,10 +1,10 @@
-// RUN: %clang -target i386-apple-darwin11 -m32 -Xarch_i386 -O3 %s -S -### 2>&1 | FileCheck -check-prefix=O3ONCE %s
-// O3ONCE: "-O3"
-// O3ONCE-NOT: "-O3"
+// RUN: %clang -target i386-apple-darwin11 -m32 -Xarch_i386 -O5 %s -S -### 2>&1 | FileCheck -check-prefix=O5ONCE %s
+// O5ONCE: "-O5"
+// O5ONCE-NOT: "-O5"
 
-// RUN: %clang -target i386-apple-darwin11 -m64 -Xarch_i386 -O3 %s -S -### 2>&1 | FileCheck -check-prefix=O3NONE %s
-// O3NONE-NOT: "-O3"
-// O3NONE: argument unused during compilation: '-Xarch_i386 -O3'
+// RUN: %clang -target i386-apple-darwin11 -m64 -Xarch_i386 -O5 %s -S -### 2>&1 | FileCheck -check-prefix=O5NONE %s
+// O5NONE-NOT: "-O5"
+// O5NONE: argument unused during compilation: '-Xarch_i386 -O5'
 
 // RUN: not %clang -target i386-apple-darwin11 -m32 -Xarch_i386 -o -Xarch_i386 -S %s -S -Xarch_i386 -o 2>&1 | FileCheck -check-prefix=INVALID %s
 // INVALID: error: invalid Xarch argument: '-Xarch_i386 -o'
diff --git a/clang/test/Driver/cl-options.c b/clang/test/Driver/cl-options.c
index 5b6dfe308a76e..2f60637f7c010 100644
--- a/clang/test/Driver/cl-options.c
+++ b/clang/test/Driver/cl-options.c
@@ -207,6 +207,10 @@
 // RUN: %clang_cl --target=i686-pc-win32 -Werror -Wno-msvc-not-found /O2 /O2 -### -- %s 2>&1 | FileCheck -check-prefix=O2O2 %s
 // O2O2: "-O2"
 
+// RUN: %clang_cl --target=i686-pc-win32 -Werror -Wno-msvc-not-found /O3 -### -- %s 2>&1 | FileCheck -check-prefix=O3 %s
+// O3: -mframe-pointer=none
+// O3: -O3
+
 // RUN: %clang_cl /Zs -Werror /Oy -- %s 2>&1
 
 // RUN: %clang_cl --target=i686-pc-win32 -Werror -Wno-msvc-not-found /Oy- -### -- %s 2>&1 | FileCheck -check-prefix=Oy_ %s