Index: include/clang/Driver/CLCompatOptions.td
===================================================================
--- include/clang/Driver/CLCompatOptions.td
+++ 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">,
@@ -252,7 +254,6 @@
 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: include/clang/Driver/Options.td
===================================================================
--- include/clang/Driver/Options.td
+++ include/clang/Driver/Options.td
@@ -1106,6 +1106,8 @@
   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: include/clang/Frontend/CodeGenOptions.def
===================================================================
--- include/clang/Frontend/CodeGenOptions.def
+++ include/clang/Frontend/CodeGenOptions.def
@@ -138,6 +138,11 @@
                                      ///< .ctors.
 VALUE_CODEGENOPT(StackAlignment    , 32, 0) ///< Overrides default stack 
                                             ///< alignment, if not 0.
+CODEGENOPT(IsStackProbeSizeOverridden, 1, 0) ///< Controls whether to use the
+                                             ///< overridden or the default
+                                             ///< stack probe size.
+VALUE_CODEGENOPT(StackProbeSize    , 32, 0) ///< Overrides default stack 
+                                            ///< probe size, even if 0.
 CODEGENOPT(DebugColumnInfo, 1, 0) ///< Whether or not to use column information
                                   ///< in debug info.
 
Index: lib/CodeGen/TargetInfo.cpp
===================================================================
--- lib/CodeGen/TargetInfo.cpp
+++ lib/CodeGen/TargetInfo.cpp
@@ -1317,18 +1317,22 @@
                                                   llvm::GlobalValue *GV,
                                             CodeGen::CodeGenModule &CGM) const {
   if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(D)) {
+    // Get the LLVM function.
+    llvm::Function *Fn = cast<llvm::Function>(GV);
+    llvm::AttrBuilder B;
+
     if (FD->hasAttr<X86ForceAlignArgPointerAttr>()) {
-      // Get the LLVM function.
-      llvm::Function *Fn = cast<llvm::Function>(GV);
-
       // Now add the 'alignstack' attribute with a value of 16.
-      llvm::AttrBuilder B;
       B.addStackAlignmentAttr(16);
-      Fn->addAttributes(llvm::AttributeSet::FunctionIndex,
-                      llvm::AttributeSet::get(CGM.getLLVMContext(),
-                                              llvm::AttributeSet::FunctionIndex,
-                                              B));
     }
+
+    if (CGM.getCodeGenOpts().IsStackProbeSizeOverridden)
+      B.addStackProbeSizeAttr(CGM.getCodeGenOpts().StackProbeSize);
+
+    Fn->addAttributes(llvm::AttributeSet::FunctionIndex,
+                    llvm::AttributeSet::get(CGM.getLLVMContext(),
+                                            llvm::AttributeSet::FunctionIndex,
+                                            B));
   }
 }
 
@@ -1539,6 +1543,9 @@
   X86_64TargetCodeGenInfo(CodeGen::CodeGenTypes &CGT, bool HasAVX)
       : TargetCodeGenInfo(new X86_64ABIInfo(CGT, HasAVX)), HasAVX(HasAVX) {}
 
+  void SetTargetAttributes(const Decl *D, llvm::GlobalValue *GV,
+                           CodeGen::CodeGenModule &CGM) const override;
+
   const X86_64ABIInfo &getABIInfo() const {
     return static_cast<const X86_64ABIInfo&>(TargetCodeGenInfo::getABIInfo());
   }
@@ -1602,6 +1609,24 @@
   }
 };
 
+void X86_64TargetCodeGenInfo::SetTargetAttributes(const Decl *D,
+                                                  llvm::GlobalValue *GV,
+                                            CodeGen::CodeGenModule &CGM) const {
+  if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(D)) {
+    if (CGM.getCodeGenOpts().IsStackProbeSizeOverridden) {
+      llvm::Function *Fn = cast<llvm::Function>(GV);
+      llvm::AttrBuilder B;
+
+      B.addStackProbeSizeAttr(CGM.getCodeGenOpts().StackProbeSize);
+
+      Fn->addAttributes(llvm::AttributeSet::FunctionIndex,
+                      llvm::AttributeSet::get(CGM.getLLVMContext(),
+                                              llvm::AttributeSet::FunctionIndex,
+                                              B));
+    }
+  }
+}
+
 static std::string qualifyWindowsLibrary(llvm::StringRef Lib) {
   // If the argument does not end in .lib, automatically add the suffix. This
   // matches the behavior of MSVC.
Index: lib/Driver/Tools.cpp
===================================================================
--- lib/Driver/Tools.cpp
+++ lib/Driver/Tools.cpp
@@ -3711,6 +3711,15 @@
     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: lib/Frontend/CompilerInvocation.cpp
===================================================================
--- lib/Frontend/CompilerInvocation.cpp
+++ lib/Frontend/CompilerInvocation.cpp
@@ -508,6 +508,18 @@
     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;
+    Opts.IsStackProbeSizeOverridden = true;
+  }
+  else
+  {
+    Opts.IsStackProbeSizeOverridden = false;
+  }
+
   if (Arg *A = Args.getLastArg(OPT_fobjc_dispatch_method_EQ)) {
     StringRef Name = A->getValue();
     unsigned Method = llvm::StringSwitch<unsigned>(Name)
Index: test/Driver/cl-options.c
===================================================================
--- test/Driver/cl-options.c
+++ 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
 
@@ -249,7 +256,6 @@
 // RUN:     /Gm- \
 // RUN:     /Gr \
 // RUN:     /GS \
-// RUN:     /Gs1000 \
 // RUN:     /GT \
 // RUN:     /GX \
 // RUN:     /Gv \