Index: cfe/trunk/include/clang/Driver/CLCompatOptions.td
===================================================================
--- cfe/trunk/include/clang/Driver/CLCompatOptions.td
+++ cfe/trunk/include/clang/Driver/CLCompatOptions.td
@@ -62,6 +62,8 @@
 def _SLASH_GR_ : CLFlag<"GR-">, HelpText<"Disable emission of RTTI data">;
 def _SLASH_GF_ : CLFlag<"GF-">, HelpText<"Disable string pooling">,
   Alias<fwritable_strings>;
+def _SLASH_Gs : CLJoined<"Gs">, HelpText<"Set stack probe size">,
+  Alias<mstack_probe_size>;
 def _SLASH_Gy : CLFlag<"Gy">, HelpText<"Put each function in its own section">,
   Alias<ffunction_sections>;
 def _SLASH_Gy_ : CLFlag<"Gy-">, HelpText<"Don't put each function in its own section">,
@@ -260,7 +262,6 @@
 def _SLASH_Gm_ : CLFlag<"Gm-">;
 def _SLASH_Gr : CLFlag<"Gr">;
 def _SLASH_GS : CLFlag<"GS">;
-def _SLASH_Gs : CLJoined<"Gs">;
 def _SLASH_GT : CLFlag<"GT">;
 def _SLASH_GX : CLFlag<"GX">;
 def _SLASH_Gv : CLFlag<"Gv">;
Index: cfe/trunk/include/clang/Driver/Options.td
===================================================================
--- cfe/trunk/include/clang/Driver/Options.td
+++ cfe/trunk/include/clang/Driver/Options.td
@@ -1129,6 +1129,8 @@
   HelpText<"Force realign the stack at entry to every function">;
 def mstack_alignment : Joined<["-"], "mstack-alignment=">, Group<m_Group>, Flags<[CC1Option]>,
   HelpText<"Set the stack alignment">;
+def mstack_probe_size : Joined<["-"], "mstack-probe-size=">, Group<m_Group>, Flags<[CC1Option]>,
+  HelpText<"Set the stack probe size">;
 def mthread_model : Separate<["-"], "mthread-model">, Group<m_Group>, Flags<[CC1Option]>,
   HelpText<"The thread model to use, e.g. posix, single (posix by default)">;
 
Index: cfe/trunk/include/clang/Frontend/CodeGenOptions.def
===================================================================
--- cfe/trunk/include/clang/Frontend/CodeGenOptions.def
+++ cfe/trunk/include/clang/Frontend/CodeGenOptions.def
@@ -138,6 +138,8 @@
                                      ///< .ctors.
 VALUE_CODEGENOPT(StackAlignment    , 32, 0) ///< Overrides default stack 
                                             ///< alignment, if not 0.
+VALUE_CODEGENOPT(StackProbeSize    , 32, 4096) ///< Overrides default stack
+                                               ///< probe size, even if 0.
 CODEGENOPT(DebugColumnInfo, 1, 0) ///< Whether or not to use column information
                                   ///< in debug info.
 
Index: cfe/trunk/lib/CodeGen/TargetInfo.cpp
===================================================================
--- cfe/trunk/lib/CodeGen/TargetInfo.cpp
+++ cfe/trunk/lib/CodeGen/TargetInfo.cpp
@@ -1616,6 +1616,9 @@
         bool d, bool p, bool w, unsigned RegParms)
     : X86_32TargetCodeGenInfo(CGT, d, p, w, RegParms) {}
 
+  void SetTargetAttributes(const Decl *D, llvm::GlobalValue *GV,
+                           CodeGen::CodeGenModule &CGM) const override;
+
   void getDependentLibraryOption(llvm::StringRef Lib,
                                  llvm::SmallString<24> &Opt) const override {
     Opt = "/DEFAULTLIB:";
@@ -1629,12 +1632,35 @@
   }
 };
 
+static void addStackProbeSizeTargetAttribute(const Decl *D,
+                                             llvm::GlobalValue *GV,
+                                             CodeGen::CodeGenModule &CGM) {
+  if (isa<FunctionDecl>(D)) {
+    if (CGM.getCodeGenOpts().StackProbeSize != 4096) {
+      llvm::Function *Fn = cast<llvm::Function>(GV);
+
+      Fn->addFnAttr("stack-probe-size", llvm::utostr(CGM.getCodeGenOpts().StackProbeSize));
+    }
+  }
+}
+
+void WinX86_32TargetCodeGenInfo::SetTargetAttributes(const Decl *D,
+                                                     llvm::GlobalValue *GV,
+                                            CodeGen::CodeGenModule &CGM) const {
+  X86_32TargetCodeGenInfo::SetTargetAttributes(D, GV, CGM);
+
+  addStackProbeSizeTargetAttribute(D, GV, CGM);
+}
+
 class WinX86_64TargetCodeGenInfo : public TargetCodeGenInfo {
   bool HasAVX;
 public:
   WinX86_64TargetCodeGenInfo(CodeGen::CodeGenTypes &CGT, bool HasAVX)
     : TargetCodeGenInfo(new WinX86_64ABIInfo(CGT)), HasAVX(HasAVX) {}
 
+  void SetTargetAttributes(const Decl *D, llvm::GlobalValue *GV,
+                           CodeGen::CodeGenModule &CGM) const override;
+
   int getDwarfEHStackPointer(CodeGen::CodeGenModule &CGM) const override {
     return 7;
   }
@@ -1666,6 +1692,13 @@
   }
 };
 
+void WinX86_64TargetCodeGenInfo::SetTargetAttributes(const Decl *D,
+                                                     llvm::GlobalValue *GV,
+                                            CodeGen::CodeGenModule &CGM) const {
+  TargetCodeGenInfo::SetTargetAttributes(D, GV, CGM);
+
+  addStackProbeSizeTargetAttribute(D, GV, CGM);
+}
 }
 
 void X86_64ABIInfo::postMerge(unsigned AggregateSize, Class &Lo,
Index: cfe/trunk/lib/Driver/Tools.cpp
===================================================================
--- cfe/trunk/lib/Driver/Tools.cpp
+++ cfe/trunk/lib/Driver/Tools.cpp
@@ -3733,6 +3733,15 @@
     CmdArgs.push_back(Args.MakeArgString("-mstack-alignment=" + alignment));
   }
 
+  if (Args.hasArg(options::OPT_mstack_probe_size)) {
+    StringRef Size = Args.getLastArgValue(options::OPT_mstack_probe_size);
+
+    if (!Size.empty())
+      CmdArgs.push_back(Args.MakeArgString("-mstack-probe-size=" + Size));
+    else
+      CmdArgs.push_back("-mstack-probe-size=0");
+  }
+
   if (getToolChain().getTriple().getArch() == llvm::Triple::aarch64 ||
       getToolChain().getTriple().getArch() == llvm::Triple::aarch64_be)
     CmdArgs.push_back("-fallow-half-arguments-and-returns");
Index: cfe/trunk/lib/Frontend/CompilerInvocation.cpp
===================================================================
--- cfe/trunk/lib/Frontend/CompilerInvocation.cpp
+++ cfe/trunk/lib/Frontend/CompilerInvocation.cpp
@@ -523,6 +523,13 @@
     Opts.StackAlignment = StackAlignment;
   }
 
+  if (Arg *A = Args.getLastArg(OPT_mstack_probe_size)) {
+    StringRef Val = A->getValue();
+    unsigned StackProbeSize = Opts.StackProbeSize;
+    Val.getAsInteger(0, StackProbeSize);
+    Opts.StackProbeSize = StackProbeSize;
+  }
+
   if (Arg *A = Args.getLastArg(OPT_fobjc_dispatch_method_EQ)) {
     StringRef Name = A->getValue();
     unsigned Method = llvm::StringSwitch<unsigned>(Name)
Index: cfe/trunk/test/Driver/cl-options.c
===================================================================
--- cfe/trunk/test/Driver/cl-options.c
+++ cfe/trunk/test/Driver/cl-options.c
@@ -42,6 +42,13 @@
 // RUN: %clang_cl /Gy /Gy- -### -- %s 2>&1 | FileCheck -check-prefix=Gy_ %s
 // Gy_-NOT: -ffunction-sections
 
+// RUN: %clang_cl /Gs -### -- %s 2>&1 | FileCheck -check-prefix=Gs %s
+// Gs: "-mstack-probe-size=0"
+// RUN: %clang_cl /Gs0 -### -- %s 2>&1 | FileCheck -check-prefix=Gs0 %s
+// Gs0: "-mstack-probe-size=0"
+// RUN: %clang_cl /Gs4096 -### -- %s 2>&1 | FileCheck -check-prefix=Gs4096 %s
+// Gs4096: "-mstack-probe-size=4096"
+
 // RUN: %clang_cl /Gw -### -- %s 2>&1 | FileCheck -check-prefix=Gw %s
 // Gw: -fdata-sections
 
@@ -245,7 +252,6 @@
 // RUN:     /Gm- \
 // RUN:     /Gr \
 // RUN:     /GS \
-// RUN:     /Gs1000 \
 // RUN:     /GT \
 // RUN:     /GX \
 // RUN:     /Gv \