[clang-cl] Support the /JMC flag

The introduction and some examples are on this page:
https://devblogs.microsoft.com/cppblog/announcing-jmc-stepping-in-visual-studio/

The `/JMC` flag enables these instrumentations:
- Insert at the beginning of every function immediately after the prologue with
  a call to `void __fastcall __CheckForDebuggerJustMyCode(unsigned char *JMC_flag)`.
  The argument for `__CheckForDebuggerJustMyCode` is the address of a boolean
  global variable (the global variable is initialized to 1) with the name
  convention `__<hash>_<filename>`. All such global variables are placed in
  the `.msvcjmc` section.
- The `<hash>` part of `__<hash>_<filename>` has a one-to-one mapping
  with a directory path. MSVC uses some unknown hashing function. Here I
  used DJB.
- Add a dummy/empty COMDAT function `__JustMyCode_Default`.
- Add `/alternatename:__CheckForDebuggerJustMyCode=__JustMyCode_Default` link
  option via ".drectve" section. This is to prevent failure in
  case `__CheckForDebuggerJustMyCode` is not provided during linking.

Implementation:
All the instrumentations are implemented in an IR codegen pass. The pass is placed immediately before CodeGenPrepare pass. This is to not interfere with mid-end optimizations and make the instrumentation target-independent (I'm still working on an ELF port in a separate patch).

Reviewed By: hans

Differential Revision: https://reviews.llvm.org/D118428

clang/docs/ReleaseNotes.rst

@@ -80,6 +80,12 @@ Attribute Changes in Clang
 Windows Support
 ---------------
 
+- Add support for MSVC-compatible ``/JMC``/``/JMC-`` flag in clang-cl (supports
+  X86/X64/ARM/ARM64). ``/JMC`` could only be used when ``/Zi`` or ``/Z7`` is
+  turned on. With this addition, clang-cl can be used in Visual Studio for the
+  JustMyCode feature. Note, you may need to manually add ``/JMC`` as additional
+  compile options in the Visual Studio since it currently assumes clang-cl does not support ``/JMC``.
+
 C Language Changes in Clang
 ---------------------------
 

clang/include/clang/Basic/CodeGenOptions.def

@@ -144,6 +144,7 @@ VALUE_CODEGENOPT(PatchableFunctionEntryOffset , 32, 0)
 CODEGENOPT(HotPatch, 1, 0) ///< Supports the Microsoft /HOTPATCH flag and
                            ///< generates a 'patchable-function' attribute.
 
+CODEGENOPT(JMCInstrument, 1, 0) ///< Set when -fjmc is enabled.
 CODEGENOPT(InstrumentForProfiling , 1, 0) ///< Set when -pg is enabled.
 CODEGENOPT(CallFEntry , 1, 0) ///< Set when -mfentry is enabled.
 CODEGENOPT(MNopMCount , 1, 0) ///< Set when -mnop-mcount is enabled.

clang/include/clang/Basic/DiagnosticDriverKinds.td

@@ -633,4 +633,8 @@ def err_drv_invalid_or_unsupported_offload_target : Error<
   "invalid or unsupported offload target: '%0'">;
 def err_drv_cuda_offload_only_emit_bc : Error<
   "CUDA offload target is supported only along with --emit-llvm">;
+
+def warn_drv_jmc_requires_debuginfo : Warning<
+  "/JMC requires debug info. Use '/Zi', '/Z7' or other debug options; option ignored">,
+  InGroup<OptionIgnored>;
 }

clang/include/clang/Driver/Options.td

@@ -1446,6 +1446,9 @@ def fno_elide_type : Flag<["-"], "fno-elide-type">, Group<f_Group>,
     HelpText<"Do not elide types when printing diagnostics">,
     MarshallingInfoNegativeFlag<DiagnosticOpts<"ElideType">>;
 def feliminate_unused_debug_symbols : Flag<["-"], "feliminate-unused-debug-symbols">, Group<f_Group>;
+def fjmc : Flag<["-"], "fjmc">, Group<f_Group>,Flags<[CC1Option]>,
+    HelpText<"Enable just-my-code debugging">,
+    MarshallingInfoFlag<CodeGenOpts<"JMCInstrument">>;
 defm eliminate_unused_debug_types : OptOutCC1FFlag<"eliminate-unused-debug-types",
   "Do not emit ", "Emit ", " debug info for defined but unused types">;
 def femit_all_decls : Flag<["-"], "femit-all-decls">, Group<f_Group>, Flags<[CC1Option]>,
@@ -6361,6 +6364,10 @@ def _SLASH_GX_ : CLFlag<"GX-">,
 def _SLASH_imsvc : CLJoinedOrSeparate<"imsvc">,
   HelpText<"Add <dir> to system include search path, as if in %INCLUDE%">,
   MetaVarName<"<dir>">;
+def _SLASH_JMC : CLFlag<"JMC">,
+  HelpText<"Enable just-my-code debugging">;
+def _SLASH_JMC_ : CLFlag<"JMC-">,
+  HelpText<"Disable just-my-code debugging (default)">;
 def _SLASH_LD : CLFlag<"LD">, HelpText<"Create DLL">;
 def _SLASH_LDd : CLFlag<"LDd">, HelpText<"Create debug DLL">;
 def _SLASH_link : CLRemainingArgsJoined<"link">,
@@ -6461,7 +6468,6 @@ def _SLASH_errorReport : CLIgnoredJoined<"errorReport">;
 def _SLASH_FC : CLIgnoredFlag<"FC">;
 def _SLASH_Fd : CLIgnoredJoined<"Fd">;
 def _SLASH_FS : CLIgnoredFlag<"FS">;
-def _SLASH_JMC : CLIgnoredFlag<"JMC">;
 def _SLASH_kernel_ : CLIgnoredFlag<"kernel-">;
 def _SLASH_nologo : CLIgnoredFlag<"nologo">;
 def _SLASH_RTC : CLIgnoredJoined<"RTC">;

clang/lib/CodeGen/BackendUtil.cpp

@@ -606,6 +606,10 @@ static bool initTargetOptions(DiagnosticsEngine &Diags,
   Options.EnableAIXExtendedAltivecABI = CodeGenOpts.EnableAIXExtendedAltivecABI;
   Options.XRayOmitFunctionIndex = CodeGenOpts.XRayOmitFunctionIndex;
   Options.LoopAlignment = CodeGenOpts.LoopAlignment;
+  Options.DebugStrictDwarf = CodeGenOpts.DebugStrictDwarf;
+  Options.ObjectFilenameForDebug = CodeGenOpts.ObjectFilenameForDebug;
+  Options.Hotpatch = CodeGenOpts.HotPatch;
+  Options.JMCInstrument = CodeGenOpts.JMCInstrument;
 
   switch (CodeGenOpts.getSwiftAsyncFramePointer()) {
   case CodeGenOptions::SwiftAsyncFramePointerKind::Auto:
@@ -644,9 +648,6 @@ static bool initTargetOptions(DiagnosticsEngine &Diags,
           Entry.IgnoreSysRoot ? Entry.Path : HSOpts.Sysroot + Entry.Path);
   Options.MCOptions.Argv0 = CodeGenOpts.Argv0;
   Options.MCOptions.CommandLineArgs = CodeGenOpts.CommandLineArgs;
-  Options.DebugStrictDwarf = CodeGenOpts.DebugStrictDwarf;
-  Options.ObjectFilenameForDebug = CodeGenOpts.ObjectFilenameForDebug;
-  Options.Hotpatch = CodeGenOpts.HotPatch;
 
   return true;
 }

clang/lib/Driver/ToolChains/Clang.cpp

@@ -7489,6 +7489,16 @@ void Clang::AddClangCLArgs(const ArgList &Args, types::ID InputType,
   }
 
   const Driver &D = getToolChain().getDriver();
+
+  // This controls whether or not we perform JustMyCode instrumentation.
+  if (Args.hasFlag(options::OPT__SLASH_JMC, options::OPT__SLASH_JMC_,
+                   /*Default=*/false)) {
+    if (*EmitCodeView && *DebugInfoKind >= codegenoptions::DebugInfoConstructor)
+      CmdArgs.push_back("-fjmc");
+    else
+      D.Diag(clang::diag::warn_drv_jmc_requires_debuginfo);
+  }
+
   EHFlags EH = parseClangCLEHFlags(D, Args);
   if (!isNVPTX && (EH.Synch || EH.Asynch)) {
     if (types::isCXX(InputType))

clang/test/Driver/cl-options.c

@@ -486,7 +486,6 @@
 // RUN:     /GZ \
 // RUN:     /H \
 // RUN:     /homeparams \
-// RUN:     /JMC \
 // RUN:     /kernel \
 // RUN:     /LN \
 // RUN:     /MP \
@@ -777,4 +776,14 @@
 // RUN: %clang_cl -target i686-pc-windows-msvc19.14.0  -### -- %s 2>&1 | FileCheck -check-prefix=TARGET %s
 // TARGET: "-triple" "i686-pc-windows-msvc19.14.0"
 
+// RUN: %clang_cl /JMC /c -### -- %s 2>&1 | FileCheck %s --check-prefix JMCWARN
+// JMCWARN: /JMC requires debug info. Use '/Zi', '/Z7' or other debug options; option ignored
+
+// RUN: %clang_cl /JMC /c -### -- %s 2>&1 | FileCheck %s --check-prefix NOJMC
+// RUN: %clang_cl /JMC /Z7 /JMC- /c -### -- %s 2>&1 | FileCheck %s --check-prefix NOJMC
+// NOJMC-NOT: -fjmc
+
+// RUN: %clang_cl /JMC /Z7 /c -### -- %s 2>&1 | FileCheck %s --check-prefix JMC
+// JMC: -fjmc
+
 void f(void) { }

llvm/include/llvm/CodeGen/CommandFlags.h

@@ -142,6 +142,8 @@ bool getDebugStrictDwarf();
 
 unsigned getAlignLoops();
 
+bool getJMCInstrument();
+
 /// Create this object with static storage to register codegen-related command
 /// line options.
 struct RegisterCodeGenFlags {

llvm/include/llvm/CodeGen/Passes.h

@@ -554,6 +554,9 @@ namespace llvm {
   /// When learning an eviction policy, extract score(reward) information,
   /// otherwise this does nothing
   FunctionPass *createRegAllocScoringPass();
+
+  /// JMC instrument pass.
+  ModulePass *createJMCInstrumenterPass();
 } // End llvm namespace
 
 #endif

llvm/include/llvm/InitializePasses.h

@@ -215,6 +215,7 @@ void initializeInterleavedAccessPass(PassRegistry&);
 void initializeInterleavedLoadCombinePass(PassRegistry &);
 void initializeInternalizeLegacyPassPass(PassRegistry&);
 void initializeIntervalPartitionPass(PassRegistry&);
+void initializeJMCInstrumenterPass(PassRegistry&);
 void initializeJumpThreadingPass(PassRegistry&);
 void initializeLCSSAVerificationPassPass(PassRegistry&);
 void initializeLCSSAWrapperPassPass(PassRegistry&);

llvm/include/llvm/LinkAllPasses.h

@@ -123,6 +123,7 @@ namespace {
       (void) llvm::createInstSimplifyLegacyPass();
       (void) llvm::createInstructionCombiningPass();
       (void) llvm::createInternalizePass();
+      (void) llvm::createJMCInstrumenterPass();
       (void) llvm::createLCSSAPass();
       (void) llvm::createLegacyDivergenceAnalysisPass();
       (void) llvm::createLICMPass();

llvm/include/llvm/Target/TargetOptions.h

@@ -142,7 +142,7 @@ namespace llvm {
           SupportsDebugEntryValues(false), EnableDebugEntryValues(false),
           ValueTrackingVariableLocations(false), ForceDwarfFrameSection(false),
           XRayOmitFunctionIndex(false), DebugStrictDwarf(false),
-          Hotpatch(false), PPCGenScalarMASSEntries(false),
+          Hotpatch(false), PPCGenScalarMASSEntries(false), JMCInstrument(false),
           FPDenormalMode(DenormalMode::IEEE, DenormalMode::IEEE) {}
 
     /// DisableFramePointerElim - This returns true if frame pointer elimination
@@ -348,6 +348,9 @@ namespace llvm {
     /// Enables scalar MASS conversions
     unsigned PPCGenScalarMASSEntries : 1;
 
+    /// Enable JustMyCode instrumentation.
+    unsigned JMCInstrument : 1;
+
     /// Name of the stack usage file (i.e., .su file) if user passes
     /// -fstack-usage. If empty, it can be implied that -fstack-usage is not
     /// passed on the command line.

llvm/lib/CodeGen/CMakeLists.txt

@@ -75,6 +75,7 @@ add_llvm_component_library(LLVMCodeGen
   InterleavedAccessPass.cpp
   InterleavedLoadCombinePass.cpp
   IntrinsicLowering.cpp
+  JMCInstrumenter.cpp
   LatencyPriorityQueue.cpp
   LazyMachineBlockFrequencyInfo.cpp
   LexicalScopes.cpp

llvm/lib/CodeGen/CodeGen.cpp

@@ -50,6 +50,7 @@ void llvm::initializeCodeGen(PassRegistry &Registry) {
   initializeIndirectBrExpandPassPass(Registry);
   initializeInterleavedLoadCombinePass(Registry);
   initializeInterleavedAccessPass(Registry);
+  initializeJMCInstrumenterPass(Registry);
   initializeLiveDebugValuesPass(Registry);
   initializeLiveDebugVariablesPass(Registry);
   initializeLiveIntervalsPass(Registry);

llvm/lib/CodeGen/CommandFlags.cpp

@@ -95,6 +95,7 @@ CGOPT(bool, ForceDwarfFrameSection)
 CGOPT(bool, XRayOmitFunctionIndex)
 CGOPT(bool, DebugStrictDwarf)
 CGOPT(unsigned, AlignLoops)
+CGOPT(bool, JMCInstrument)
 
 codegen::RegisterCodeGenFlags::RegisterCodeGenFlags() {
 #define CGBINDOPT(NAME)                                                        \
@@ -464,6 +465,12 @@ codegen::RegisterCodeGenFlags::RegisterCodeGenFlags() {
                                       cl::desc("Default alignment for loops"));
   CGBINDOPT(AlignLoops);
 
+  static cl::opt<bool> JMCInstrument(
+      "enable-jmc-instrument",
+      cl::desc("Instrument functions with a call to __CheckForDebuggerJustMyCode"),
+      cl::init(false));
+  CGBINDOPT(JMCInstrument);
+
 #undef CGBINDOPT
 
   mc::RegisterMCTargetOptionsFlags();
@@ -539,6 +546,7 @@ codegen::InitTargetOptionsFromCodeGenFlags(const Triple &TheTriple) {
   Options.XRayOmitFunctionIndex = getXRayOmitFunctionIndex();
   Options.DebugStrictDwarf = getDebugStrictDwarf();
   Options.LoopAlignment = getAlignLoops();
+  Options.JMCInstrument = getJMCInstrument();
 
   Options.MCOptions = mc::InitMCTargetOptionsFromFlags();
 

llvm/lib/CodeGen/JMCInstrumenter.cpp

@@ -0,0 +1,207 @@
+//===- JMCInstrumenter.cpp - JMC Instrumentation --------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// JMCInstrumenter pass:
+// - add "/alternatename:__CheckForDebuggerJustMyCode=__JustMyCode_Default" to
+//   "llvm.linker.options"
+// - create the dummy COMDAT function __JustMyCode_Default
+// - instrument each function with a call to __CheckForDebuggerJustMyCode. The
+//   sole argument should be defined in .msvcjmc. Each flag is 1 byte initilized
+//   to 1.
+// - (TODO) currently targeting MSVC, adds ELF debuggers support
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/SmallString.h"
+#include "llvm/ADT/StringExtras.h"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/IR/DIBuilder.h"
+#include "llvm/IR/DebugInfoMetadata.h"
+#include "llvm/IR/DerivedTypes.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/Type.h"
+#include "llvm/InitializePasses.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/DJB.h"
+#include "llvm/Support/Path.h"
+#include "llvm/Transforms/Utils/ModuleUtils.h"
+
+using namespace llvm;
+
+#define DEBUG_TYPE "jmc-instrument"
+
+namespace {
+struct JMCInstrumenter : public ModulePass {
+  static char ID;
+  JMCInstrumenter() : ModulePass(ID) {
+    initializeJMCInstrumenterPass(*PassRegistry::getPassRegistry());
+  }
+  bool runOnModule(Module &M) override;
+};
+char JMCInstrumenter::ID = 0;
+} // namespace
+
+INITIALIZE_PASS(
+    JMCInstrumenter, DEBUG_TYPE,
+    "Instrument function entry with call to __CheckForDebuggerJustMyCode",
+    false, false)
+
+ModulePass *llvm::createJMCInstrumenterPass() { return new JMCInstrumenter(); }
+
+namespace {
+const char CheckFunctionName[] = "__CheckForDebuggerJustMyCode";
+
+std::string getFlagName(DISubprogram &SP, bool UseX86FastCall) {
+  // Best effort path normalization. This is to guarantee an unique flag symbol
+  // is produced for the same directory. Some builds may want to use relative
+  // paths, or paths with a specific prefix (see the -fdebug-compilation-dir
+  // flag), so only hash paths in debuginfo. Don't expand them to absolute
+  // paths.
+  SmallString<256> FilePath(SP.getDirectory());
+  sys::path::append(FilePath, SP.getFilename());
+  sys::path::native(FilePath);
+  sys::path::remove_dots(FilePath, /*remove_dot_dot=*/true);
+
+  // The naming convention for the flag name is __<hash>_<file name> with '.' in
+  // <file name> replaced with '@'. For example C:\file.any.c would have a flag
+  // __D032E919_file@any@c. The naming convention match MSVC's format however
+  // the match is not required to make JMC work. The hashing function used here
+  // is different from MSVC's.
+
+  std::string Suffix;
+  for (auto C : sys::path::filename(FilePath))
+    Suffix.push_back(C == '.' ? '@' : C);
+
+  sys::path::remove_filename(FilePath);
+  return (UseX86FastCall ? "_" : "__") +
+         utohexstr(djbHash(FilePath), /*LowerCase=*/false,
+                   /*Width=*/8) +
+         "_" + Suffix;
+}
+
+void attachDebugInfo(GlobalVariable &GV, DISubprogram &SP) {
+  Module &M = *GV.getParent();
+  DICompileUnit *CU = SP.getUnit();
+  assert(CU);
+  DIBuilder DB(M, false, CU);
+
+  auto *DType =
+      DB.createBasicType("unsigned char", 8, dwarf::DW_ATE_unsigned_char,
+                         llvm::DINode::FlagArtificial);
+
+  auto *DGVE = DB.createGlobalVariableExpression(
+      CU, GV.getName(), /*LinkageName=*/StringRef(), SP.getFile(),
+      /*LineNo=*/0, DType, /*IsLocalToUnit=*/true, /*IsDefined=*/true);
+  GV.addMetadata(LLVMContext::MD_dbg, *DGVE);
+  DB.finalize();
+}
+
+FunctionType *getCheckFunctionType(LLVMContext &Ctx) {
+  Type *VoidTy = Type::getVoidTy(Ctx);
+  PointerType *VoidPtrTy = Type::getInt8PtrTy(Ctx);
+  return FunctionType::get(VoidTy, VoidPtrTy, false);
+}
+
+void createDefaultCheckFunction(Module &M, bool UseX86FastCall) {
+  LLVMContext &Ctx = M.getContext();
+  const char *DefaultCheckFunctionName =
+      UseX86FastCall ? "_JustMyCode_Default" : "__JustMyCode_Default";
+  // Create the function.
+  Function *DefaultCheckFunc =
+      Function::Create(getCheckFunctionType(Ctx), GlobalValue::ExternalLinkage,
+                       DefaultCheckFunctionName, &M);
+  DefaultCheckFunc->setUnnamedAddr(GlobalValue::UnnamedAddr::Global);
+  DefaultCheckFunc->addParamAttr(0, Attribute::NoUndef);
+  if (UseX86FastCall)
+    DefaultCheckFunc->addParamAttr(0, Attribute::InReg);
+  appendToUsed(M, {DefaultCheckFunc});
+  Comdat *C = M.getOrInsertComdat(DefaultCheckFunctionName);
+  C->setSelectionKind(Comdat::Any);
+  DefaultCheckFunc->setComdat(C);
+  BasicBlock *EntryBB = BasicBlock::Create(Ctx, "", DefaultCheckFunc);
+  ReturnInst::Create(Ctx, EntryBB);
+
+  // Add a linker option /alternatename to set the default implementation for
+  // the check function.
+  // https://devblogs.microsoft.com/oldnewthing/20200731-00/?p=104024
+  std::string AltOption = std::string("/alternatename:") + CheckFunctionName +
+                          "=" + DefaultCheckFunctionName;
+  llvm::Metadata *Ops[] = {llvm::MDString::get(Ctx, AltOption)};
+  MDTuple *N = MDNode::get(Ctx, Ops);
+  M.getOrInsertNamedMetadata("llvm.linker.options")->addOperand(N);
+}
+} // namespace
+
+bool JMCInstrumenter::runOnModule(Module &M) {
+  bool Changed = false;
+  LLVMContext &Ctx = M.getContext();
+  Triple ModuleTriple(M.getTargetTriple());
+  bool UseX86FastCall =
+      ModuleTriple.isOSWindows() && ModuleTriple.getArch() == Triple::x86;
+
+  Function *CheckFunction = nullptr;
+  DenseMap<DISubprogram *, Constant *> SavedFlags(8);
+  for (auto &F : M) {
+    if (F.isDeclaration())
+      continue;
+    auto *SP = F.getSubprogram();
+    if (!SP)
+      continue;
+
+    Constant *&Flag = SavedFlags[SP];
+    if (!Flag) {
+      std::string FlagName = getFlagName(*SP, UseX86FastCall);
+      IntegerType *FlagTy = Type::getInt8Ty(Ctx);
+      Flag = M.getOrInsertGlobal(FlagName, FlagTy, [&] {
+        // FIXME: Put the GV in comdat and have linkonce_odr linkage to save
+        //        .msvcjmc section space? maybe not worth it.
+        GlobalVariable *GV = new GlobalVariable(
+            M, FlagTy, /*isConstant=*/false, GlobalValue::InternalLinkage,
+            ConstantInt::get(FlagTy, 1), FlagName);
+        GV->setSection(".msvcjmc");
+        GV->setAlignment(Align(1));
+        GV->setUnnamedAddr(GlobalValue::UnnamedAddr::Global);
+        attachDebugInfo(*GV, *SP);
+        return GV;
+      });
+    }
+
+    if (!CheckFunction) {
+      assert(!M.getFunction(CheckFunctionName) &&
+             "JMC instrument more than once?");
+      CheckFunction = cast<Function>(
+          M.getOrInsertFunction(CheckFunctionName, getCheckFunctionType(Ctx))
+              .getCallee());
+      CheckFunction->setUnnamedAddr(GlobalValue::UnnamedAddr::Global);
+      CheckFunction->addParamAttr(0, Attribute::NoUndef);
+      if (UseX86FastCall) {
+        CheckFunction->setCallingConv(CallingConv::X86_FastCall);
+        CheckFunction->addParamAttr(0, Attribute::InReg);
+      }
+    }
+    // FIXME: it would be nice to make CI scheduling boundary, although in
+    //        practice it does not matter much.
+    auto *CI = CallInst::Create(CheckFunction, {Flag}, "",
+                                &*F.begin()->getFirstInsertionPt());
+    CI->addParamAttr(0, Attribute::NoUndef);
+    if (UseX86FastCall) {
+      CI->setCallingConv(CallingConv::X86_FastCall);
+      CI->addParamAttr(0, Attribute::InReg);
+    }
+
+    Changed = true;
+  }
+  if (!Changed)
+    return false;
+
+  createDefaultCheckFunction(M, UseX86FastCall);
+  return true;
+}

llvm/lib/Target/AArch64/AArch64TargetMachine.cpp

@@ -574,6 +574,9 @@ void AArch64PassConfig::addIRPasses() {
   // Add Control Flow Guard checks.
   if (TM->getTargetTriple().isOSWindows())
     addPass(createCFGuardCheckPass());
+
+  if (TM->Options.JMCInstrument)
+    addPass(createJMCInstrumenterPass());
 }
 
 // Pass Pipeline Configuration

llvm/lib/Target/ARM/ARMTargetMachine.cpp

@@ -434,6 +434,9 @@ void ARMPassConfig::addIRPasses() {
   // Add Control Flow Guard checks.
   if (TM->getTargetTriple().isOSWindows())
     addPass(createCFGuardCheckPass());
+
+  if (TM->Options.JMCInstrument)
+    addPass(createJMCInstrumenterPass());
 }
 
 void ARMPassConfig::addCodeGenPrepare() {

llvm/lib/Target/X86/X86TargetMachine.cpp

@@ -441,6 +441,9 @@ void X86PassConfig::addIRPasses() {
       addPass(createCFGuardCheckPass());
     }
   }
+
+  if (TM->Options.JMCInstrument)
+    addPass(createJMCInstrumenterPass());
 }
 
 bool X86PassConfig::addInstSelector() {

llvm/test/Instrumentation/JustMyCode/jmc-instrument-x86.ll

@@ -0,0 +1,53 @@
+; RUN: opt -jmc-instrument -S < %s | FileCheck %s
+
+; CHECK: $_JustMyCode_Default = comdat any
+
+; CHECK: @"_A85D9D03_x@c" = internal unnamed_addr global i8 1, section ".msvcjmc", align 1, !dbg !0
+; CHECK: @llvm.used = appending global [1 x i8*] [i8* bitcast (void (i8*)* @_JustMyCode_Default to i8*)], section "llvm.metadata"
+
+; CHECK: define void @w1() #0 !dbg !10 {
+; CHECK:   call x86_fastcallcc void @__CheckForDebuggerJustMyCode(i8* inreg noundef @"_A85D9D03_x@c")
+; CHECK:   ret void
+; CHECK: }
+
+; CHECK: declare x86_fastcallcc void @__CheckForDebuggerJustMyCode(i8* inreg noundef) unnamed_addr
+
+; CHECK: define void @_JustMyCode_Default(i8* inreg noundef %0) unnamed_addr comdat {
+; CHECK:   ret void
+; CHECK: }
+
+; CHECK: !0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+; CHECK: !1 = distinct !DIGlobalVariable(name: "_A85D9D03_x@c", scope: !2, file: !3, type: !5, isLocal: true, isDefinition: true)
+; CHECK: !2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, globals: !4, splitDebugInlining: false, nameTableKind: None)
+; CHECK: !3 = !DIFile(filename: "./b/./../b/x.c", directory: "C:\\\\a\\\\")
+; CHECK: !4 = !{!0}
+; CHECK: !5 = !DIBasicType(name: "unsigned char", size: 8, encoding: DW_ATE_unsigned_char, flags: DIFlagArtificial)
+; CHECK: !6 = !{i32 2, !"CodeView", i32 1}
+; CHECK: !7 = !{i32 2, !"Debug Info Version", i32 3}
+; CHECK: !8 = !{!"clang"}
+; CHECK: !9 = !{!"/alternatename:__CheckForDebuggerJustMyCode=_JustMyCode_Default"}
+; CHECK: !10 = distinct !DISubprogram(name: "w1", scope: !3, file: !3, line: 1, type: !11, scopeLine: 1, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !13)
+; CHECK: !11 = !DISubroutineType(types: !12)
+
+target datalayout = "e-m:x-p:32:32-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32-a:0:32-S32"
+target triple = "i386-pc-windows-msvc"
+
+define void @w1() #0 !dbg !10 {
+  ret void
+}
+
+attributes #0 = { "target-cpu"="pentium4" "target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!7, !8}
+!llvm.ident = !{!9}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "./b/./../b/x.c", directory: "C:\\\\a\\\\")
+!7 = !{i32 2, !"CodeView", i32 1}
+!8 = !{i32 2, !"Debug Info Version", i32 3}
+!9 = !{!"clang"}
+!10 = distinct !DISubprogram(name: "w1", scope: !1, file: !1, line: 1, type: !31, scopeLine: 1, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !33)
+!31 = !DISubroutineType(types: !32)
+!32 = !{null}
+!33 = !{}

llvm/test/Instrumentation/JustMyCode/jmc-instrument.ll

@@ -0,0 +1,120 @@
+; RUN: opt -jmc-instrument -mtriple=x86_64-pc-windows-msvc  -S < %s | FileCheck %s
+; RUN: opt -jmc-instrument -mtriple=aarch64-pc-windows-msvc -S < %s | FileCheck %s
+; RUN: opt -jmc-instrument -mtriple=arm-pc-windows-msvc     -S < %s | FileCheck %s
+
+; CHECK: $__JustMyCode_Default = comdat any
+
+; CHECK: @"__7DF23CF5_x@c" = internal unnamed_addr global i8 1, section ".msvcjmc", align 1, !dbg !0
+; CHECK: @"__A85D9D03_x@c" = internal unnamed_addr global i8 1, section ".msvcjmc", align 1, !dbg !5
+; CHECK: @llvm.used = appending global [1 x i8*] [i8* bitcast (void (i8*)* @__JustMyCode_Default to i8*)], section "llvm.metadata"
+
+; CHECK: define void @l1() !dbg !13 {
+; CHECK:   call void @__CheckForDebuggerJustMyCode(i8* noundef @"__7DF23CF5_x@c")
+; CHECK:   ret void
+; CHECK: }
+
+; CHECK: define void @l2() !dbg !17 {
+; CHECK:   call void @__CheckForDebuggerJustMyCode(i8* noundef @"__7DF23CF5_x@c")
+; CHECK:   ret void
+; CHECK: }
+
+; CHECK: define void @w1() !dbg !19 {
+; CHECK:   call void @__CheckForDebuggerJustMyCode(i8* noundef @"__A85D9D03_x@c")
+; CHECK:   ret void
+; CHECK: }
+
+; CHECK: define void @w2() !dbg !20 {
+; CHECK:   call void @__CheckForDebuggerJustMyCode(i8* noundef @"__A85D9D03_x@c")
+; CHECK:   ret void
+; CHECK: }
+
+; CHECK: define void @w3() !dbg !22 {
+; CHECK:   call void @__CheckForDebuggerJustMyCode(i8* noundef @"__A85D9D03_x@c")
+; CHECK:   ret void
+; CHECK: }
+
+; CHECK: define void @w4() !dbg !24 {
+; CHECK:   call void @__CheckForDebuggerJustMyCode(i8* noundef @"__A85D9D03_x@c")
+; CHECK:   ret void
+; CHECK: }
+
+; CHECK: declare void @__CheckForDebuggerJustMyCode(i8* noundef) unnamed_addr
+
+; CHECK: define void @__JustMyCode_Default(i8* noundef %0) unnamed_addr comdat {
+; CHECK:   ret void
+; CHECK: }
+
+; CHECK: !llvm.linker.options = !{!12}
+
+; CHECK: !0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+; CHECK: !1 = distinct !DIGlobalVariable(name: "__7DF23CF5_x@c", scope: !2, file: !3, type: !8, isLocal: true, isDefinition: true)
+; CHECK: !2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, globals: !4, splitDebugInlining: false, nameTableKind: None)
+; CHECK: !3 = !DIFile(filename: "a/x.c", directory: "/tmp")
+; CHECK: !4 = !{!0, !5}
+; CHECK: !5 = !DIGlobalVariableExpression(var: !6, expr: !DIExpression())
+; CHECK: !6 = distinct !DIGlobalVariable(name: "__A85D9D03_x@c", scope: !2, file: !7, type: !8, isLocal: true, isDefinition: true)
+; CHECK: !7 = !DIFile(filename: "./x.c", directory: "C:\\\\a\\\\b\\\\")
+; CHECK: !8 = !DIBasicType(name: "unsigned char", size: 8, encoding: DW_ATE_unsigned_char, flags: DIFlagArtificial)
+; CHECK: !9 = !{i32 2, !"CodeView", i32 1}
+; CHECK: !10 = !{i32 2, !"Debug Info Version", i32 3}
+; CHECK: !11 = !{!"clang"}
+; CHECK: !12 = !{!"/alternatename:__CheckForDebuggerJustMyCode=__JustMyCode_Default"}
+; CHECK: !13 = distinct !DISubprogram(name: "f", scope: !3, file: !3, line: 1, type: !14, scopeLine: 1, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !16)
+; CHECK: !14 = !DISubroutineType(types: !15)
+; CHECK: !15 = !{null}
+; CHECK: !16 = !{}
+; CHECK: !17 = distinct !DISubprogram(name: "f", scope: !18, file: !18, line: 1, type: !14, scopeLine: 1, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !16)
+; CHECK: !18 = !DIFile(filename: "x.c", directory: "/tmp/a")
+; CHECK: !19 = distinct !DISubprogram(name: "f", scope: !7, file: !7, line: 1, type: !14, scopeLine: 1, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !16)
+; CHECK: !20 = distinct !DISubprogram(name: "f", scope: !21, file: !21, line: 1, type: !14, scopeLine: 1, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !16)
+; CHECK: !21 = !DIFile(filename: "./b\\x.c", directory: "C:\\\\a\\\\")
+; CHECK: !22 = distinct !DISubprogram(name: "f", scope: !23, file: !23, line: 1, type: !14, scopeLine: 1, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !16)
+; CHECK: !23 = !DIFile(filename: "./b/x.c", directory: "C:\\\\a\\\\")
+; CHECK: !24 = distinct !DISubprogram(name: "f", scope: !25, file: !25, line: 1, type: !14, scopeLine: 1, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !16)
+; CHECK: !25 = !DIFile(filename: "./b/./../b/x.c", directory: "C:\\\\a")
+
+; All use the same flag
+define void @l1() !dbg !10 {
+  ret void
+}
+define void @l2() !dbg !11 {
+  ret void
+}
+
+; All use the same flag
+define void @w1() !dbg !12 {
+  ret void
+}
+define void @w2() !dbg !13 {
+  ret void
+}
+define void @w3() !dbg !14 {
+  ret void
+}
+define void @w4() !dbg !15 {
+  ret void
+}
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!7, !8}
+!llvm.ident = !{!9}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "a/x.c", directory: "/tmp")
+!2 = !DIFile(filename: "x.c", directory: "/tmp/a")
+!3 = !DIFile(filename: "./x.c", directory: "C:\\\\a\\\\b\\\\")
+!4 = !DIFile(filename: "./b\\x.c", directory: "C:\\\\a\\\\")
+!5 = !DIFile(filename: "./b/x.c", directory: "C:\\\\a\\\\")
+!6 = !DIFile(filename: "./b/./../b/x.c", directory: "C:\\\\a")
+!7 = !{i32 2, !"CodeView", i32 1}
+!8 = !{i32 2, !"Debug Info Version", i32 3}
+!9 = !{!"clang"}
+!10 = distinct !DISubprogram(name: "f", scope: !1, file: !1, line: 1, type: !31, scopeLine: 1, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !33)
+!11 = distinct !DISubprogram(name: "f", scope: !2, file: !2, line: 1, type: !31, scopeLine: 1, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !33)
+!12 = distinct !DISubprogram(name: "f", scope: !3, file: !3, line: 1, type: !31, scopeLine: 1, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !33)
+!13 = distinct !DISubprogram(name: "f", scope: !4, file: !4, line: 1, type: !31, scopeLine: 1, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !33)
+!14 = distinct !DISubprogram(name: "f", scope: !5, file: !5, line: 1, type: !31, scopeLine: 1, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !33)
+!15 = distinct !DISubprogram(name: "f", scope: !6, file: !6, line: 1, type: !31, scopeLine: 1, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !33)
+!31 = !DISubroutineType(types: !32)
+!32 = !{null}
+!33 = !{}

llvm/tools/opt/opt.cpp

@@ -498,7 +498,8 @@ static bool shouldPinPassToLegacyPM(StringRef Pass) {
       "generic-to-nvvm",      "expandmemcmp",
       "loop-reduce",          "lower-amx-type",
       "pre-amx-config",       "lower-amx-intrinsics",
-      "polyhedral-info",      "replace-with-veclib"};
+      "polyhedral-info",      "replace-with-veclib",
+      "jmc-instrument"};
   for (const auto &P : PassNamePrefix)
     if (Pass.startswith(P))
       return true;
@@ -572,6 +573,7 @@ int main(int argc, char **argv) {
   initializeHardwareLoopsPass(Registry);
   initializeTypePromotionPass(Registry);
   initializeReplaceWithVeclibLegacyPass(Registry);
+  initializeJMCInstrumenterPass(Registry);
 
 #ifdef BUILD_EXAMPLES
   initializeExampleIRTransforms(Registry);