Index: include/clang/Driver/CLCompatOptions.td
===================================================================
--- include/clang/Driver/CLCompatOptions.td
+++ include/clang/Driver/CLCompatOptions.td
@@ -109,18 +109,25 @@
   Alias<I>;
 def _SLASH_J : CLFlag<"J">, HelpText<"Make char type unsigned">,
   Alias<funsigned_char>;
-def _SLASH_O0 : CLFlag<"O0">, Alias<O0>;
-// /Oy- is handled by the /O option because /Oy- only has an effect on 32-bit.
-def _SLASH_O : CLJoined<"O">, HelpText<"Optimization level">;
-def _SLASH_Od : CLFlag<"Od">, HelpText<"Disable optimization">, Alias<O0>;
-def _SLASH_Oi : CLFlag<"Oi">, HelpText<"Enable use of builtin functions">,
-  Alias<fbuiltin>;
-def _SLASH_Oi_ : CLFlag<"Oi-">, HelpText<"Disable use of builtin functions">,
-  Alias<fno_builtin>;
-def _SLASH_Os : CLFlag<"Os">, HelpText<"Optimize for size">, Alias<O>,
-  AliasArgs<["s"]>;
-def _SLASH_Ot : CLFlag<"Ot">, HelpText<"Optimize for speed">, Alias<O>,
-  AliasArgs<["2"]>;
+
+// The _SLASH_O option handles all the /O variants, but we also provide separate aliased options to provide separate help messages.
+def _SLASH_O : CLJoined<"O">, HelpText<"Set the optimization level">, MetaVarName<"[0|1|2|b{0123}|d|g|i[-]|s|t|x|y[-]]">;
+def _SLASH_O0 : CLFlag<"O0">, Alias<O0>, HelpText<"Disable optimization">;
+def _SLASH_O1 : CLFlag<"O1">, Alias<_SLASH_O>, AliasArgs<["1"]>, HelpText<"Optimize for small size (equivalent to /Og /Os /Oy /Ob2 /Gs /GF /Gy)">;
+def _SLASH_O2 : CLFlag<"O2">, Alias<_SLASH_O>, AliasArgs<["2"]>, HelpText<"Optimize for maximum speed (equivalent to /Og /Oi /Ot /Oy /Ob2 /Gs /GF /Gy)">;
+def _SLASH_Ob0 : CLFlag<"Ob0">, Alias<_SLASH_O>, AliasArgs<["b0"]>, HelpText<"Disable inlining">;
+def _SLASH_Ob1 : CLFlag<"Ob1">, Alias<_SLASH_O>, AliasArgs<["b1"]>, HelpText<"Inline functions which are (explicitly or implicitly) marked inline">;
+def _SLASH_Ob2 : CLFlag<"Ob2">, Alias<_SLASH_O>, AliasArgs<["b2"]>, HelpText<"Inline suitable functions">;
+def _SLASH_Od : CLFlag<"Od">, Alias<O0>, HelpText<"Disable optimization">;
+def _SLASH_Og : CLFlag<"Og">, Alias<_SLASH_O>, AliasArgs<["g"]>;
+def _SLASH_Oi : CLFlag<"Oi">, Alias<_SLASH_O>, AliasArgs<["i"]>, HelpText<"Optimize using builtin knowledge of functions">;
+def _SLASH_Oi_ : CLFlag<"Oi-">, Alias<_SLASH_O>, AliasArgs<["i-"]>, HelpText<"Disable optimization based on builtin knowledge of functions">;
+def _SLASH_Os : CLFlag<"Os">, Alias<_SLASH_O>, AliasArgs<["s"]>, HelpText<"Optimize for small size over speed">;
+def _SLASH_Ot : CLFlag<"Ot">, Alias<_SLASH_O>, AliasArgs<["t"]>, HelpText<"Optimize for speed over small size">;
+def _SLASH_Ox : CLFlag<"Ox">, Alias<_SLASH_O>, AliasArgs<["x"]>, HelpText<"Optimize maximum speed (equivalent to /Og /Oi /Ot /Oy /Ob2)">;
+def _SLASH_Oy : CLFlag<"Oy">, Alias<_SLASH_O>, AliasArgs<["y"]>, HelpText<"Enable frame pointer omission (x86 only)">;
+def _SLASH_Oy_ : CLFlag<"Oy-">, Alias<_SLASH_O>, AliasArgs<["y-"]>, HelpText<"Disable frame pointer omission (x86 only)">;
+
 def _SLASH_QUESTION : CLFlag<"?">, Alias<help>,
   HelpText<"Display available options">;
 def _SLASH_Qvec : CLFlag<"Qvec">,
@@ -329,7 +336,6 @@
 def _SLASH_GF : CLIgnoredFlag<"GF">;
 def _SLASH_kernel_ : CLIgnoredFlag<"kernel-">;
 def _SLASH_nologo : CLIgnoredFlag<"nologo">;
-def _SLASH_Og : CLIgnoredFlag<"Og">;
 def _SLASH_openmp_ : CLIgnoredFlag<"openmp-">;
 def _SLASH_permissive_ : CLIgnoredFlag<"permissive-">;
 def _SLASH_RTC : CLIgnoredJoined<"RTC">;
Index: lib/Driver/ToolChains/MSVC.cpp
===================================================================
--- lib/Driver/ToolChains/MSVC.cpp
+++ lib/Driver/ToolChains/MSVC.cpp
@@ -1378,6 +1378,7 @@
       }
       break;
     case 'g':
+      A->claim();
       break;
     case 'i':
       if (I + 1 != E && OptStr[I + 1] == '-') {
Index: test/Driver/Xarch.c
===================================================================
--- test/Driver/Xarch.c
+++ test/Driver/Xarch.c
@@ -1,8 +1,8 @@
-// RUN: %clang -target i386-apple-darwin9 -m32 -Xarch_i386 -O2 %s -S -### 2> %t.log
-// RUN: grep ' "-O2" ' %t.log | count 1
-// RUN: %clang -target i386-apple-darwin9 -m64 -Xarch_i386 -O2 %s -S -### 2> %t.log
-// RUN: not grep ' "-O2" ' %t.log
-// RUN: grep "argument unused during compilation: '-Xarch_i386 -O2'" %t.log
+// RUN: %clang -target i386-apple-darwin9 -m32 -Xarch_i386 -O3 %s -S -### 2> %t.log
+// RUN: grep ' "-O3" ' %t.log | count 1
+// RUN: %clang -target i386-apple-darwin9 -m64 -Xarch_i386 -O3 %s -S -### 2> %t.log
+// RUN: not grep ' "-O3" ' %t.log
+// RUN: grep "argument unused during compilation: '-Xarch_i386 -O3'" %t.log
 // RUN: not %clang -target i386-apple-darwin9 -m32 -Xarch_i386 -o -Xarch_i386 -S %s -S -Xarch_i386 -o 2> %t.log
 // RUN: grep "error: invalid Xarch argument: '-Xarch_i386 -o'" %t.log | count 2
 // RUN: grep "error: invalid Xarch argument: '-Xarch_i386 -S'" %t.log