Index: include/llvm/CodeGen/CommandFlags.h
===================================================================
--- include/llvm/CodeGen/CommandFlags.h
+++ include/llvm/CodeGen/CommandFlags.h
@@ -256,6 +256,7 @@
   Options.JTType = JTableType;
 
   Options.ThreadModel = TMModel;
+  Options.NoRedZone = DisableRedZone;
 
   return Options;
 }
Index: include/llvm/Target/TargetOptions.h
===================================================================
--- include/llvm/Target/TargetOptions.h
+++ include/llvm/Target/TargetOptions.h
@@ -70,8 +70,8 @@
           EnableFastISel(false), PositionIndependentExecutable(false),
           UseInitArray(false), DisableIntegratedAS(false),
           CompressDebugSections(false), FunctionSections(false),
-          DataSections(false), TrapUnreachable(false), TrapFuncName(""),
-          FloatABIType(FloatABI::Default),
+          DataSections(false), TrapUnreachable(false), NoRedZone(false),
+          TrapFuncName(""), FloatABIType(FloatABI::Default),
           AllowFPOpFusion(FPOpFusion::Standard), JTType(JumpTable::Single),
           ThreadModel(ThreadModel::POSIX) {}
 
@@ -192,6 +192,16 @@
     /// Emit target-specific trap instruction for 'unreachable' IR instructions.
     unsigned TrapUnreachable : 1;
 
+    /// NoRedZone - This flag is enabled when the -disable-red-zone flag is
+    /// specified on the command line.  When this flag is off (the default),
+    /// leaf functions may use unallocated stack space.  This optimization
+    /// eliminates stack adjustment instructions. For example, in
+    /// x86_64 targets, red zone use results in insructions with negative
+    /// stack offsets, as in -8(%rsp).  Red Zone optimization is unsafe
+    /// where hardware preemption such as interrupt handling may overwrite
+    /// unallocated stack space.
+    unsigned NoRedZone : 1;
+
     /// getTrapFunctionName - If this returns a non-empty string, this means
     /// isel should lower Intrinsic::trap to a call to the specified function
     /// name instead of an ISD::TRAP node.
@@ -258,6 +268,7 @@
     ARE_EQUAL(PositionIndependentExecutable) &&
     ARE_EQUAL(UseInitArray) &&
     ARE_EQUAL(TrapUnreachable) &&
+    ARE_EQUAL(NoRedZone) &&
     ARE_EQUAL(TrapFuncName) &&
     ARE_EQUAL(FloatABIType) &&
     ARE_EQUAL(AllowFPOpFusion) &&
Index: lib/Target/X86/X86FrameLowering.cpp
===================================================================
--- lib/Target/X86/X86FrameLowering.cpp
+++ lib/Target/X86/X86FrameLowering.cpp
@@ -517,6 +517,7 @@
       !MFI->adjustsStack() &&                           // No calls.
       !IsWin64 &&                                       // Win64 has no Red Zone
       !usesTheStack(MF) &&                              // Don't push and pop.
+      !MF.getTarget().Options.NoRedZone &&              // command line
       !MF.shouldSplitStack()) {                         // Regular stack
     uint64_t MinSize = X86FI->getCalleeSavedFrameSize();
     if (HasFP) MinSize += SlotSize;
Index: test/CodeGen/X86/red-zone.ll
===================================================================
--- test/CodeGen/X86/red-zone.ll
+++ test/CodeGen/X86/red-zone.ll
@@ -1,4 +1,5 @@
 ; RUN: llc < %s -mcpu=generic -mtriple=x86_64-linux | FileCheck %s
+; RUN: llc < %s -mcpu=generic -disable-red-zone -mtriple=x86_64-linux | FileCheck %s --check-prefix=CMDLINE
 
 ; First without noredzone.
 ; CHECK-LABEL: f0:
@@ -11,7 +12,7 @@
 	ret x86_fp80 %0
 }
 
-; Then with noredzone.
+; Then with noredzone function attribute.
 ; CHECK-LABEL: f1:
 ; CHECK: subq $4, %rsp
 ; CHECK: (%rsp)
@@ -23,3 +24,11 @@
 	%0 = fpext float %f to x86_fp80		; <x86_fp80> [#uses=1]
 	ret x86_fp80 %0
 }
+
+; Then with -disable-red-zone on command line
+; CMDLINE-LABEL: f0:
+; CMDLINE: subq $4, %rsp
+; CMDLINE: (%rsp)
+; CMDLINE: (%rsp)
+; CMDLINE: addq $4, %rsp
+; CMDLINE: ret