diff --git a/clang/docs/ShadowCallStack.rst b/clang/docs/ShadowCallStack.rst
--- a/clang/docs/ShadowCallStack.rst
+++ b/clang/docs/ShadowCallStack.rst
@@ -9,7 +9,7 @@
 ============
 
 ShadowCallStack is an instrumentation pass, currently only implemented for
-aarch64 and x86_64, that protects programs against return address overwrites
+aarch64, that protects programs against return address overwrites
 (e.g. stack buffer overflows.) It works by saving a function's return address
 to a separately allocated 'shadow call stack' in the function prolog in
 non-leaf functions and loading the return address from the shadow call stack
@@ -18,11 +18,10 @@
 
 The aarch64 implementation is considered production ready, and
 an `implementation of the runtime`_ has been added to Android's libc
-(bionic). The x86_64 implementation was evaluated using Chromium and was
-found to have critical performance and security deficiencies, and may be
-removed in a future release of the compiler. This document only describes
-the aarch64 implementation; details on the x86_64 implementation are found
-in the `Clang 7.0.1 documentation`_.
+(bionic). An x86_64 implementation was evaluated using Chromium and was found
+to have critical performance and security deficiencies--it was removed in
+LLVM 9.0. Details on the x86_64 implementation can be found in the
+`Clang 7.0.1 documentation`_.
 
 .. _`implementation of the runtime`: https://android.googlesource.com/platform/bionic/+/808d176e7e0dd727c7f929622ec017f6e065c582/libc/bionic/pthread_create.cpp#128
 .. _`Clang 7.0.1 documentation`: https://releases.llvm.org/7.0.1/tools/clang/docs/ShadowCallStack.html
@@ -37,10 +36,9 @@
 memory accesses.
 
 `Return Flow Guard`_ is a pure software implementation of shadow call stacks
-on x86_64. It is similar to the ShadowCallStack x86_64 implementation but
-trades off higher memory usage for a shorter prologue and epilogue. Like
-x86_64 ShadowCallStack, it is inherently racy due to the architecture's use
-of the stack for calls and returns.
+on x86_64. Like the previous implementation of ShadowCallStack on x86_64, it is
+inherently racy due to the architecture's use of the stack for calls and
+returns.
 
 Intel `Control-flow Enforcement Technology`_ (CET) is a proposed hardware
 extension that would add native support to use a shadow stack to store/check
diff --git a/compiler-rt/cmake/config-ix.cmake b/compiler-rt/cmake/config-ix.cmake
--- a/compiler-rt/cmake/config-ix.cmake
+++ b/compiler-rt/cmake/config-ix.cmake
@@ -254,7 +254,7 @@
 else()
 set(ALL_XRAY_SUPPORTED_ARCH ${X86_64} ${ARM32} ${ARM64} ${MIPS32} ${MIPS64} powerpc64le)
 endif()
-set(ALL_SHADOWCALLSTACK_SUPPORTED_ARCH ${X86_64} ${ARM64})
+set(ALL_SHADOWCALLSTACK_SUPPORTED_ARCH ${ARM64})
 
 if(APPLE)
   include(CompilerRTDarwinUtils)
diff --git a/compiler-rt/test/shadowcallstack/libc_support.h b/compiler-rt/test/shadowcallstack/libc_support.h
--- a/compiler-rt/test/shadowcallstack/libc_support.h
+++ b/compiler-rt/test/shadowcallstack/libc_support.h
@@ -33,9 +33,5 @@
 }
 
 #else
-
-__attribute__((noinline)) void scs_fputs_stdout(const char *p) {
-  fputs(p, stdout);
-}
-
+#error Unsupported platform
 #endif
diff --git a/compiler-rt/test/shadowcallstack/lit.cfg b/compiler-rt/test/shadowcallstack/lit.cfg
--- a/compiler-rt/test/shadowcallstack/lit.cfg
+++ b/compiler-rt/test/shadowcallstack/lit.cfg
@@ -19,5 +19,5 @@
   scs_arch_cflags += ' -ffixed-x18 '
 config.substitutions.append( ("%clang_scs ", config.clang + ' -O0 -fsanitize=shadow-call-stack ' + scs_arch_cflags + ' ') )
 
-if config.host_os not in ['Linux'] or config.target_arch not in ['x86_64', 'aarch64']:
+if config.host_os not in ['Linux'] or config.target_arch not in ['aarch64']:
    config.unsupported = True
diff --git a/compiler-rt/test/shadowcallstack/minimal_runtime.h b/compiler-rt/test/shadowcallstack/minimal_runtime.h
--- a/compiler-rt/test/shadowcallstack/minimal_runtime.h
+++ b/compiler-rt/test/shadowcallstack/minimal_runtime.h
@@ -4,10 +4,6 @@
 
 #pragma once
 
-#ifdef __x86_64__
-#include <asm/prctl.h>
-int arch_prctl(int code, void *addr);
-#endif
 #include <stdlib.h>
 #include <sys/mman.h>
 #include <sys/prctl.h>
@@ -21,10 +17,7 @@
   if (stack == MAP_FAILED)
     abort();
 
-#if defined(__x86_64__)
-  if (arch_prctl(ARCH_SET_GS, stack))
-    abort();
-#elif defined(__aarch64__)
+#if defined(__aarch64__)
   __asm__ __volatile__("mov x18, %0" ::"r"(stack));
 #else
 #error Unsupported platform
diff --git a/compiler-rt/test/shadowcallstack/overflow-aarch64.c b/compiler-rt/test/shadowcallstack/overflow-aarch64.c
deleted file mode 100644
--- a/compiler-rt/test/shadowcallstack/overflow-aarch64.c
+++ /dev/null
@@ -1,5 +0,0 @@
-// See overflow.c for a description.
-
-// REQUIRES: aarch64-target-arch
-// RUN: %clang_scs %S/overflow.c -o %t -DITERATIONS=12
-// RUN: %run %t | FileCheck %S/overflow.c
diff --git a/compiler-rt/test/shadowcallstack/overflow-x86_64.c b/compiler-rt/test/shadowcallstack/overflow-x86_64.c
deleted file mode 100644
--- a/compiler-rt/test/shadowcallstack/overflow-x86_64.c
+++ /dev/null
@@ -1,5 +0,0 @@
-// See overflow.c for a description.
-
-// REQUIRES: x86_64-target-arch
-// RUN: %clang_scs %S/overflow.c -o %t -DITERATIONS=12
-// RUN: not --crash %run %t
diff --git a/compiler-rt/test/shadowcallstack/overflow.c b/compiler-rt/test/shadowcallstack/overflow.c
--- a/compiler-rt/test/shadowcallstack/overflow.c
+++ b/compiler-rt/test/shadowcallstack/overflow.c
@@ -8,12 +8,10 @@
 // RUN: %clang_scs %s -o %t -DITERATIONS=3
 // RUN: %run %t | FileCheck %s
 
-// The behavioral check for SCS + overflow lives in the tests overflow-x86_64.c
-// and overflow-aarch64.c. This is because the expected behavior is different
-// between the two platforms. On x86_64 we crash because the comparison between
-// the shadow call stack and the regular stack fails. On aarch64 there is no
-// comparison, we just load the return address from the shadow call stack. So we
-// just expect not to see the output from print_and_exit.
+// On aarch64 we just load the return address from the shadow call stack so we
+// do not expect to see the output from print_and_exit.
+// RUN: %clang_scs %s -o %t -DITERATIONS=12
+// RUN: %run %t | FileCheck %S/overflow.c
 
 #include <stdio.h>
 #include <stdlib.h>
diff --git a/llvm/lib/Target/X86/CMakeLists.txt b/llvm/lib/Target/X86/CMakeLists.txt
--- a/llvm/lib/Target/X86/CMakeLists.txt
+++ b/llvm/lib/Target/X86/CMakeLists.txt
@@ -22,7 +22,6 @@
 add_public_tablegen_target(X86CommonTableGen)
 
 set(sources
-  ShadowCallStack.cpp
   X86AsmPrinter.cpp
   X86CallFrameOptimization.cpp
   X86CallingConv.cpp
diff --git a/llvm/lib/Target/X86/ShadowCallStack.cpp b/llvm/lib/Target/X86/ShadowCallStack.cpp
deleted file mode 100644
--- a/llvm/lib/Target/X86/ShadowCallStack.cpp
+++ /dev/null
@@ -1,321 +0,0 @@
-//===------- ShadowCallStack.cpp - Shadow Call Stack pass -----------------===//
-//
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-//===----------------------------------------------------------------------===//
-//
-// The ShadowCallStack pass instruments function prologs/epilogs to check that
-// the return address has not been corrupted during the execution of the
-// function. The return address is stored in a 'shadow call stack' addressed
-// using the %gs segment register.
-//
-//===----------------------------------------------------------------------===//
-
-#include "X86.h"
-#include "X86InstrBuilder.h"
-#include "X86InstrInfo.h"
-#include "X86Subtarget.h"
-
-#include "llvm/CodeGen/MachineFunction.h"
-#include "llvm/CodeGen/MachineFunctionPass.h"
-#include "llvm/CodeGen/MachineInstrBuilder.h"
-#include "llvm/CodeGen/MachineModuleInfo.h"
-#include "llvm/CodeGen/MachineRegisterInfo.h"
-#include "llvm/CodeGen/Passes.h"
-#include "llvm/CodeGen/TargetInstrInfo.h"
-#include "llvm/Pass.h"
-#include "llvm/Support/raw_ostream.h"
-
-using namespace llvm;
-
-namespace {
-
-class ShadowCallStack : public MachineFunctionPass {
-public:
-  static char ID;
-
-  ShadowCallStack() : MachineFunctionPass(ID) {
-    initializeShadowCallStackPass(*PassRegistry::getPassRegistry());
-  }
-
-  void getAnalysisUsage(AnalysisUsage &AU) const override {
-    MachineFunctionPass::getAnalysisUsage(AU);
-  }
-
-  bool runOnMachineFunction(MachineFunction &Fn) override;
-
-private:
-  // Do not instrument leaf functions with this many or fewer instructions. The
-  // shadow call stack instrumented prolog/epilog are slightly race-y reading
-  // and checking the saved return address, so it is better to not instrument
-  // functions that have fewer instructions than the instrumented prolog/epilog
-  // race.
-  static const size_t SkipLeafInstructions = 3;
-};
-
-char ShadowCallStack::ID = 0;
-} // end anonymous namespace.
-
-static void addProlog(MachineFunction &Fn, const TargetInstrInfo *TII,
-                      MachineBasicBlock &MBB, const DebugLoc &DL);
-static void addPrologLeaf(MachineFunction &Fn, const TargetInstrInfo *TII,
-                          MachineBasicBlock &MBB, const DebugLoc &DL,
-                          MCPhysReg FreeRegister);
-
-static void addEpilog(const TargetInstrInfo *TII, MachineBasicBlock &MBB,
-                      MachineInstr &MI, MachineBasicBlock &TrapBB);
-static void addEpilogLeaf(const TargetInstrInfo *TII, MachineBasicBlock &MBB,
-                          MachineInstr &MI, MachineBasicBlock &TrapBB,
-                          MCPhysReg FreeRegister);
-// Generate a longer epilog that only uses r10 when a tailcall branches to r11.
-static void addEpilogOnlyR10(const TargetInstrInfo *TII, MachineBasicBlock &MBB,
-                             MachineInstr &MI, MachineBasicBlock &TrapBB);
-
-// Helper function to add ModR/M references for [Seg: Reg + Offset] memory
-// accesses
-static inline const MachineInstrBuilder &
-addSegmentedMem(const MachineInstrBuilder &MIB, MCPhysReg Seg, MCPhysReg Reg,
-                int Offset = 0) {
-  return MIB.addReg(Reg).addImm(1).addReg(0).addImm(Offset).addReg(Seg);
-}
-
-static void addProlog(MachineFunction &Fn, const TargetInstrInfo *TII,
-                      MachineBasicBlock &MBB, const DebugLoc &DL) {
-  const MCPhysReg ReturnReg = X86::R10;
-  const MCPhysReg OffsetReg = X86::R11;
-
-  auto MBBI = MBB.begin();
-  // mov r10, [rsp]
-  addDirectMem(BuildMI(MBB, MBBI, DL, TII->get(X86::MOV64rm)).addDef(ReturnReg),
-               X86::RSP);
-  // xor r11, r11
-  BuildMI(MBB, MBBI, DL, TII->get(X86::XOR64rr))
-      .addDef(OffsetReg)
-      .addReg(OffsetReg, RegState::Undef)
-      .addReg(OffsetReg, RegState::Undef);
-  // add QWORD [gs:r11], 8
-  addSegmentedMem(BuildMI(MBB, MBBI, DL, TII->get(X86::ADD64mi8)), X86::GS,
-                  OffsetReg)
-      .addImm(8);
-  // mov r11, [gs:r11]
-  addSegmentedMem(
-      BuildMI(MBB, MBBI, DL, TII->get(X86::MOV64rm)).addDef(OffsetReg), X86::GS,
-      OffsetReg);
-  // mov [gs:r11], r10
-  addSegmentedMem(BuildMI(MBB, MBBI, DL, TII->get(X86::MOV64mr)), X86::GS,
-                  OffsetReg)
-      .addReg(ReturnReg);
-}
-
-static void addPrologLeaf(MachineFunction &Fn, const TargetInstrInfo *TII,
-                          MachineBasicBlock &MBB, const DebugLoc &DL,
-                          MCPhysReg FreeRegister) {
-  // mov REG, [rsp]
-  addDirectMem(BuildMI(MBB, MBB.begin(), DL, TII->get(X86::MOV64rm))
-                   .addDef(FreeRegister),
-               X86::RSP);
-}
-
-static void addEpilog(const TargetInstrInfo *TII, MachineBasicBlock &MBB,
-                      MachineInstr &MI, MachineBasicBlock &TrapBB) {
-  const DebugLoc &DL = MI.getDebugLoc();
-
-  // xor r11, r11
-  BuildMI(MBB, MI, DL, TII->get(X86::XOR64rr))
-      .addDef(X86::R11)
-      .addReg(X86::R11, RegState::Undef)
-      .addReg(X86::R11, RegState::Undef);
-  // mov r10, [gs:r11]
-  addSegmentedMem(BuildMI(MBB, MI, DL, TII->get(X86::MOV64rm)).addDef(X86::R10),
-                  X86::GS, X86::R11);
-  // mov r10, [gs:r10]
-  addSegmentedMem(BuildMI(MBB, MI, DL, TII->get(X86::MOV64rm)).addDef(X86::R10),
-                  X86::GS, X86::R10);
-  // sub QWORD [gs:r11], 8
-  // This instruction should not be moved up to avoid a signal race.
-  addSegmentedMem(BuildMI(MBB, MI, DL, TII->get(X86::SUB64mi8)),
-                  X86::GS, X86::R11)
-      .addImm(8);
-  // cmp [rsp], r10
-  addDirectMem(BuildMI(MBB, MI, DL, TII->get(X86::CMP64mr)), X86::RSP)
-      .addReg(X86::R10);
-  // jne trap
-  BuildMI(MBB, MI, DL, TII->get(X86::JNE_1)).addMBB(&TrapBB);
-  MBB.addSuccessor(&TrapBB);
-}
-
-static void addEpilogLeaf(const TargetInstrInfo *TII, MachineBasicBlock &MBB,
-                          MachineInstr &MI, MachineBasicBlock &TrapBB,
-                          MCPhysReg FreeRegister) {
-  const DebugLoc &DL = MI.getDebugLoc();
-
-  // cmp [rsp], REG
-  addDirectMem(BuildMI(MBB, MI, DL, TII->get(X86::CMP64mr)), X86::RSP)
-      .addReg(FreeRegister);
-  // jne trap
-  BuildMI(MBB, MI, DL, TII->get(X86::JNE_1)).addMBB(&TrapBB);
-  MBB.addSuccessor(&TrapBB);
-}
-
-static void addEpilogOnlyR10(const TargetInstrInfo *TII, MachineBasicBlock &MBB,
-                             MachineInstr &MI, MachineBasicBlock &TrapBB) {
-  const DebugLoc &DL = MI.getDebugLoc();
-
-  // xor r10, r10
-  BuildMI(MBB, MI, DL, TII->get(X86::XOR64rr))
-      .addDef(X86::R10)
-      .addReg(X86::R10, RegState::Undef)
-      .addReg(X86::R10, RegState::Undef);
-  // mov r10, [gs:r10]
-  addSegmentedMem(BuildMI(MBB, MI, DL, TII->get(X86::MOV64rm)).addDef(X86::R10),
-                  X86::GS, X86::R10);
-  // mov r10, [gs:r10]
-  addSegmentedMem(BuildMI(MBB, MI, DL, TII->get(X86::MOV64rm)).addDef(X86::R10),
-                  X86::GS, X86::R10);
-  // sub QWORD [gs:0], 8
-  // This instruction should not be moved up to avoid a signal race.
-  addSegmentedMem(BuildMI(MBB, MI, DL, TII->get(X86::SUB64mi8)), X86::GS, 0)
-      .addImm(8);
-  // cmp [rsp], r10
-  addDirectMem(BuildMI(MBB, MI, DL, TII->get(X86::CMP64mr)), X86::RSP)
-      .addReg(X86::R10);
-  // jne trap
-  BuildMI(MBB, MI, DL, TII->get(X86::JNE_1)).addMBB(&TrapBB);
-  MBB.addSuccessor(&TrapBB);
-}
-
-bool ShadowCallStack::runOnMachineFunction(MachineFunction &Fn) {
-  if (!Fn.getFunction().hasFnAttribute(Attribute::ShadowCallStack) ||
-      Fn.getFunction().hasFnAttribute(Attribute::Naked))
-    return false;
-
-  if (Fn.empty() || !Fn.getRegInfo().tracksLiveness())
-    return false;
-
-  // FIXME: Skip functions that have r10 or r11 live on entry (r10 can be live
-  // on entry for parameters with the nest attribute.)
-  if (Fn.front().isLiveIn(X86::R10) || Fn.front().isLiveIn(X86::R11))
-    return false;
-
-  // FIXME: Skip functions with conditional and r10 tail calls for now.
-  bool HasReturn = false;
-  for (auto &MBB : Fn) {
-    if (MBB.empty())
-      continue;
-
-    const MachineInstr &MI = MBB.instr_back();
-    if (MI.isReturn())
-      HasReturn = true;
-
-    if (MI.isReturn() && MI.isCall()) {
-      if (MI.findRegisterUseOperand(X86::EFLAGS))
-        return false;
-      // This should only be possible on Windows 64 (see GR64_TC versus
-      // GR64_TCW64.)
-      if (MI.findRegisterUseOperand(X86::R10) ||
-          MI.hasRegisterImplicitUseOperand(X86::R10))
-        return false;
-    }
-  }
-
-  if (!HasReturn)
-    return false;
-
-  // For leaf functions:
-  // 1. Do not instrument very short functions where it would not improve that
-  //    function's security.
-  // 2. Detect if there is an unused caller-saved register we can reserve to
-  //    hold the return address instead of writing/reading it from the shadow
-  //    call stack.
-  MCPhysReg LeafFuncRegister = X86::NoRegister;
-  if (!Fn.getFrameInfo().adjustsStack()) {
-    size_t InstructionCount = 0;
-    std::bitset<X86::NUM_TARGET_REGS> UsedRegs;
-    for (auto &MBB : Fn) {
-      for (auto &LiveIn : MBB.liveins())
-        UsedRegs.set(LiveIn.PhysReg);
-      for (auto &MI : MBB) {
-        if (!MI.isDebugValue() && !MI.isCFIInstruction() && !MI.isLabel())
-          InstructionCount++;
-        for (auto &Op : MI.operands())
-          if (Op.isReg() && Op.isDef())
-            UsedRegs.set(Op.getReg());
-      }
-    }
-
-    if (InstructionCount <= SkipLeafInstructions)
-      return false;
-
-    std::bitset<X86::NUM_TARGET_REGS> CalleeSavedRegs;
-    const MCPhysReg *CSRegs = Fn.getRegInfo().getCalleeSavedRegs();
-    for (size_t i = 0; CSRegs[i]; i++)
-      CalleeSavedRegs.set(CSRegs[i]);
-
-    const TargetRegisterInfo *TRI = Fn.getSubtarget().getRegisterInfo();
-    for (auto &Reg : X86::GR64_NOSPRegClass.getRegisters()) {
-      // FIXME: Optimization opportunity: spill/restore a callee-saved register
-      // if a caller-saved register is unavailable.
-      if (CalleeSavedRegs.test(Reg))
-        continue;
-
-      bool Used = false;
-      for (MCSubRegIterator SR(Reg, TRI, true); SR.isValid(); ++SR)
-        if ((Used = UsedRegs.test(*SR)))
-          break;
-
-      if (!Used) {
-        LeafFuncRegister = Reg;
-        break;
-      }
-    }
-  }
-
-  const bool LeafFuncOptimization = LeafFuncRegister != X86::NoRegister;
-  if (LeafFuncOptimization)
-    // Mark the leaf function register live-in for all MBBs except the entry MBB
-    for (auto I = ++Fn.begin(), E = Fn.end(); I != E; ++I)
-      I->addLiveIn(LeafFuncRegister);
-
-  MachineBasicBlock &MBB = Fn.front();
-  const MachineBasicBlock *NonEmpty = MBB.empty() ? MBB.getFallThrough() : &MBB;
-  const DebugLoc &DL = NonEmpty->front().getDebugLoc();
-
-  const TargetInstrInfo *TII = Fn.getSubtarget().getInstrInfo();
-  if (LeafFuncOptimization)
-    addPrologLeaf(Fn, TII, MBB, DL, LeafFuncRegister);
-  else
-    addProlog(Fn, TII, MBB, DL);
-
-  MachineBasicBlock *Trap = nullptr;
-  for (auto &MBB : Fn) {
-    if (MBB.empty())
-      continue;
-
-    MachineInstr &MI = MBB.instr_back();
-    if (MI.isReturn()) {
-      if (!Trap) {
-        Trap = Fn.CreateMachineBasicBlock();
-        BuildMI(Trap, MI.getDebugLoc(), TII->get(X86::TRAP));
-        Fn.push_back(Trap);
-      }
-
-      if (LeafFuncOptimization)
-        addEpilogLeaf(TII, MBB, MI, *Trap, LeafFuncRegister);
-      else if (MI.findRegisterUseOperand(X86::R11))
-        addEpilogOnlyR10(TII, MBB, MI, *Trap);
-      else
-        addEpilog(TII, MBB, MI, *Trap);
-    }
-  }
-
-  return true;
-}
-
-INITIALIZE_PASS(ShadowCallStack, "shadow-call-stack", "Shadow Call Stack",
-                false, false)
-
-FunctionPass *llvm::createShadowCallStackPass() {
-  return new ShadowCallStack();
-}
diff --git a/llvm/lib/Target/X86/X86.h b/llvm/lib/Target/X86/X86.h
--- a/llvm/lib/Target/X86/X86.h
+++ b/llvm/lib/Target/X86/X86.h
@@ -49,11 +49,6 @@
 /// transition penalty between functions encoded with AVX and SSE.
 FunctionPass *createX86IssueVZeroUpperPass();
 
-/// This pass instruments the function prolog to save the return address to a
-/// 'shadow call stack' and the function epilog to check that the return address
-/// did not change during function execution.
-FunctionPass *createShadowCallStackPass();
-
 /// This pass inserts ENDBR instructions before indirect jump/call
 /// destinations as part of CET IBT mechanism.
 FunctionPass *createX86IndirectBranchTrackingPass();
@@ -137,7 +132,6 @@
 void initializeEvexToVexInstPassPass(PassRegistry &);
 void initializeFixupBWInstPassPass(PassRegistry &);
 void initializeFixupLEAPassPass(PassRegistry &);
-void initializeShadowCallStackPass(PassRegistry &);
 void initializeWinEHStatePassPass(PassRegistry &);
 void initializeX86AvoidSFBPassPass(PassRegistry &);
 void initializeX86CallFrameOptimizationPass(PassRegistry &);
diff --git a/llvm/lib/Target/X86/X86TargetMachine.cpp b/llvm/lib/Target/X86/X86TargetMachine.cpp
--- a/llvm/lib/Target/X86/X86TargetMachine.cpp
+++ b/llvm/lib/Target/X86/X86TargetMachine.cpp
@@ -69,7 +69,6 @@
   initializeFixupBWInstPassPass(PR);
   initializeEvexToVexInstPassPass(PR);
   initializeFixupLEAPassPass(PR);
-  initializeShadowCallStackPass(PR);
   initializeX86CallFrameOptimizationPass(PR);
   initializeX86CmovConverterPassPass(PR);
   initializeX86ExecutionDomainFixPass(PR);
@@ -489,7 +488,6 @@
     addPass(createBreakFalseDeps());
   }
 
-  addPass(createShadowCallStackPass());
   addPass(createX86IndirectBranchTrackingPass());
 
   if (UseVZeroUpper)
diff --git a/llvm/test/CodeGen/X86/O0-pipeline.ll b/llvm/test/CodeGen/X86/O0-pipeline.ll
--- a/llvm/test/CodeGen/X86/O0-pipeline.ll
+++ b/llvm/test/CodeGen/X86/O0-pipeline.ll
@@ -55,7 +55,6 @@
 ; CHECK-NEXT:       Post-RA pseudo instruction expansion pass
 ; CHECK-NEXT:       X86 pseudo instruction expansion pass
 ; CHECK-NEXT:       Analyze Machine Code For Garbage Collection
-; CHECK-NEXT:       Shadow Call Stack
 ; CHECK-NEXT:       X86 Indirect Branch Tracking
 ; CHECK-NEXT:       X86 vzeroupper inserter
 ; CHECK-NEXT:       X86 Discriminate Memory Operands
diff --git a/llvm/test/CodeGen/X86/O3-pipeline.ll b/llvm/test/CodeGen/X86/O3-pipeline.ll
--- a/llvm/test/CodeGen/X86/O3-pipeline.ll
+++ b/llvm/test/CodeGen/X86/O3-pipeline.ll
@@ -150,7 +150,6 @@
 ; CHECK-NEXT:       ReachingDefAnalysis
 ; CHECK-NEXT:       X86 Execution Dependency Fix
 ; CHECK-NEXT:       BreakFalseDeps
-; CHECK-NEXT:       Shadow Call Stack
 ; CHECK-NEXT:       X86 Indirect Branch Tracking
 ; CHECK-NEXT:       X86 vzeroupper inserter
 ; CHECK-NEXT:       MachineDominator Tree Construction
diff --git a/llvm/test/CodeGen/X86/shadow-call-stack.mir b/llvm/test/CodeGen/X86/shadow-call-stack.mir
deleted file mode 100644
--- a/llvm/test/CodeGen/X86/shadow-call-stack.mir
+++ /dev/null
@@ -1,212 +0,0 @@
-# RUN: llc -mtriple=x86_64-unknown-linux-gnu -run-pass shadow-call-stack -verify-machineinstrs -o - %s | FileCheck %s
---- |
-
-  define void @no_return() #0 { ret void }
-  define void @normal_return() #0 { ret void }
-  define void @normal_return_leaf_func() #0 { ret void }
-  define void @short_leaf_func() #0 { ret void }
-  define void @normal_tail_call() #0 { ret void }
-  define void @r11_tail_call() #0 { ret void }
-  define void @conditional_tail_call() #0 { ret void }
-  define void @r10_live_in() #0 { ret void }
-
-  attributes #0 = { shadowcallstack }
-
-...
----
-# CHECK-LABEL: name: no_return
-name: no_return
-tracksRegLiveness: true
-frameInfo:
-  adjustsStack: true # not a leaf function
-body: |
-  ; CHECK: bb.0:
-  bb.0:
-    ; CHECK-NEXT: $eax = MOV32ri 13
-    $eax = MOV32ri 13
-...
----
-# CHECK-LABEL: name: normal_return
-name: normal_return
-tracksRegLiveness: true
-frameInfo:
-  adjustsStack: true # not a leaf function
-body: |
-  ; CHECK: bb.0:
-  bb.0:
-    ; CHECK: $r10 = MOV64rm $rsp, 1, $noreg, 0, $noreg
-    ; CHECK-NEXT: $r11 = XOR64rr undef $r11, undef $r11, implicit-def $eflags
-    ; CHECK-NEXT: ADD64mi8 $r11, 1, $noreg, 0, $gs, 8, implicit-def $eflags
-    ; CHECK-NEXT: $r11 = MOV64rm $r11, 1, $noreg, 0, $gs
-    ; CHECK-NEXT: MOV64mr $r11, 1, $noreg, 0, $gs, $r10
-    ; CHECK-NEXT: $eax = MOV32ri 13
-    $eax = MOV32ri 13
-
-    ; CHECK-NEXT: $r11 = XOR64rr undef $r11, undef $r11, implicit-def $eflags
-    ; CHECK-NEXT: $r10 = MOV64rm $r11, 1, $noreg, 0, $gs
-    ; CHECK-NEXT: $r10 = MOV64rm $r10, 1, $noreg, 0, $gs
-    ; CHECK-NEXT: SUB64mi8 $r11, 1, $noreg, 0, $gs, 8, implicit-def $eflags
-    ; CHECK-NEXT: CMP64mr $rsp, 1, $noreg, 0, $noreg, $r10, implicit-def $eflags
-    ; CHECK-NEXT: JNE_1 %bb.1, implicit $eflags
-    ; CHECK-NEXT: RETQ $eax
-    RETQ $eax
-
-    ; CHECK: bb.1:
-    ; CHECK-NEXT; TRAP
-...
----
-# CHECK-LABEL: name: normal_return_leaf_func
-name: normal_return_leaf_func
-tracksRegLiveness: true
-frameInfo:
-  adjustsStack: false # leaf function
-body: |
-  ; CHECK: bb.0:
-  ; CHECK: liveins: $rcx
-  bb.0:
-    liveins: $rcx
-
-    ; CHECK: $rdx = MOV64rm $rsp, 1, $noreg, 0, $noreg
-    ; CHECK-NEXT: $eax = MOV32ri 0
-    $eax = MOV32ri 0
-    ; CHECK-NEXT: CMP64ri8 $rcx, 5, implicit-def $eflags
-    CMP64ri8 $rcx, 5, implicit-def $eflags
-    ; CHECK-NEXT: JA_1 %bb.1, implicit $eflags
-    JA_1 %bb.1, implicit $eflags
-    ; CHECK-NEXT: JMP_1 %bb.2
-    JMP_1 %bb.2
-
-  ; CHECK: bb.1
-  ; CHECK: liveins: $eax, $rdx
-  bb.1:
-    liveins: $eax
-
-    ; CHECKT: $eax = MOV32ri 1
-    $eax = MOV32ri 1
-
-  ; CHECK: bb.2
-  ; CHECK: liveins: $eax, $rdx
-  bb.2:
-    liveins: $eax
-
-    ; CHECK: CMP64mr $rsp, 1, $noreg, 0, $noreg, $rdx, implicit-def $eflags
-    ; CHECK-NEXT: JNE_1 %bb.3, implicit $eflags
-    ; CHECK-NEXT: RETQ $eax
-    RETQ $eax
-
-    ; CHECK: bb.3:
-    ; CHECK-NEXT; TRAP
-...
----
-# CHECK-LABEL: name: short_leaf_func
-name: short_leaf_func
-tracksRegLiveness: true
-frameInfo:
-  adjustsStack: false # leaf function
-body: |
-  ; CHECK: bb.0:
-  bb.0:
-    ; Ensure these are not counted as machine instructions
-    CFI_INSTRUCTION 0
-    CFI_INSTRUCTION 0
-    CFI_INSTRUCTION 0
-    DBG_VALUE 0
-    DBG_VALUE 0
-    DBG_VALUE 0
-
-    ; CHECK: $eax = MOV32ri 13
-    $eax = MOV32ri 13
-
-    ; CHECK-NEXT: RETQ $eax
-    RETQ $eax
-...
----
-# CHECK-LABEL: name: normal_tail_call
-name: normal_tail_call
-tracksRegLiveness: true
-frameInfo:
-  adjustsStack: true # not a leaf function
-body: |
-  ; CHECK: bb.0:
-  bb.0:
-    ; CHECK: $r10 = MOV64rm $rsp, 1, $noreg, 0, $noreg
-    ; CHECK-NEXT: $r11 = XOR64rr undef $r11, undef $r11, implicit-def $eflags
-    ; CHECK-NEXT: ADD64mi8 $r11, 1, $noreg, 0, $gs, 8, implicit-def $eflags
-    ; CHECK-NEXT: $r11 = MOV64rm $r11, 1, $noreg, 0, $gs
-    ; CHECK-NEXT: MOV64mr $r11, 1, $noreg, 0, $gs, $r10
-    ; CHECK-NEXT: $eax = MOV32ri 13
-    $eax = MOV32ri 13
-
-    ; CHECK-NEXT: $r11 = XOR64rr undef $r11, undef $r11, implicit-def $eflags
-    ; CHECK-NEXT: $r10 = MOV64rm $r11, 1, $noreg, 0, $gs
-    ; CHECK-NEXT: $r10 = MOV64rm $r10, 1, $noreg, 0, $gs
-    ; CHECK-NEXT: SUB64mi8 $r11, 1, $noreg, 0, $gs, 8, implicit-def $eflags
-    ; CHECK-NEXT: CMP64mr $rsp, 1, $noreg, 0, $noreg, $r10, implicit-def $eflags
-    ; CHECK-NEXT: JNE_1 %bb.1, implicit $eflags
-    ; CHECK-NEXT: TAILJMPr64 $rax
-    TAILJMPr64 $rax
-
-    ; CHECK: bb.1:
-    ; CHECK-NEXT; TRAP
-...
----
-# CHECK-LABEL: name: r11_tail_call
-name: r11_tail_call
-tracksRegLiveness: true
-frameInfo:
-  adjustsStack: true # not a leaf function
-body: |
-  ; CHECK: bb.0:
-  bb.0:
-    ; CHECK: $r10 = MOV64rm $rsp, 1, $noreg, 0, $noreg
-    ; CHECK-NEXT: $r11 = XOR64rr undef $r11, undef $r11, implicit-def $eflags
-    ; CHECK-NEXT: ADD64mi8 $r11, 1, $noreg, 0, $gs, 8, implicit-def $eflags
-    ; CHECK-NEXT: $r11 = MOV64rm $r11, 1, $noreg, 0, $gs
-    ; CHECK-NEXT: MOV64mr $r11, 1, $noreg, 0, $gs, $r10
-    ; CHECK-NEXT: $eax = MOV32ri 13
-    $eax = MOV32ri 13
-
-    ; CHECK-NEXT: $r10 = XOR64rr undef $r10, undef $r10, implicit-def $eflags
-    ; CHECK-NEXT: $r10 = MOV64rm $r10, 1, $noreg, 0, $gs
-    ; CHECK-NEXT: $r10 = MOV64rm $r10, 1, $noreg, 0, $gs
-    ; CHECK-NEXT: SUB64mi8 $noreg, 1, $noreg, 0, $gs, 8, implicit-def $eflags
-    ; CHECK-NEXT: CMP64mr $rsp, 1, $noreg, 0, $noreg, $r10, implicit-def $eflags
-    ; CHECK-NEXT: JNE_1 %bb.1, implicit $eflags
-    ; CHECK-NEXT: TAILJMPr64 undef $r11
-    TAILJMPr64 undef $r11
-
-    ; CHECK: bb.1:
-    ; CHECK-NEXT; TRAP
-...
----
-# CHECK-LABEL: name: conditional_tail_call
-name: conditional_tail_call
-tracksRegLiveness: true
-frameInfo:
-  adjustsStack: true # not a leaf function
-body: |
-  ; CHECK: bb.0:
-  bb.0:
-    ; CHECK: $eax = MOV32ri 13
-    $eax = MOV32ri 13
-
-    ; CHECK-NEXT: TAILJMPd64_CC @conditional_tail_call, undef $eflags
-    TAILJMPd64_CC @conditional_tail_call, undef $eflags
-...
----
-# CHECK-LABEL: name: r10_live_in
-name: r10_live_in
-tracksRegLiveness: true
-frameInfo:
-  adjustsStack: true # not a leaf function
-body: |
-  ; CHECK: bb.0:
-  ; CHECK: liveins: $r10
-  bb.0:
-    liveins: $r10
-
-    ; CHECK: $eax = MOV32ri 13
-    $eax = MOV32ri 13
-    ; CHECK-NEXT: RETQ $eax
-    RETQ $eax
-...
diff --git a/llvm/utils/gn/secondary/llvm/lib/Target/X86/BUILD.gn b/llvm/utils/gn/secondary/llvm/lib/Target/X86/BUILD.gn
--- a/llvm/utils/gn/secondary/llvm/lib/Target/X86/BUILD.gn
+++ b/llvm/utils/gn/secondary/llvm/lib/Target/X86/BUILD.gn
@@ -76,7 +76,6 @@
     deps += [ ":X86GenFoldTables" ]
   }
   sources = [
-    "ShadowCallStack.cpp",
     "X86AsmPrinter.cpp",
     "X86AvoidStoreForwardingBlocks.cpp",
     "X86CallFrameOptimization.cpp",