[MC][re-land] Omit DWARF unwind info if compact unwind is present where eligible

This reverts commit d941d59783.

Differential Revision: https://reviews.llvm.org/D122258

clang/include/clang/Basic/CodeGenOptions.def

@@ -114,6 +114,10 @@ CODEGENOPT(StackSizeSection  , 1, 0) ///< Set when -fstack-size-section is enabl
 CODEGENOPT(ForceDwarfFrameSection , 1, 0) ///< Set when -fforce-dwarf-frame is
                                           ///< enabled.
 
+///< Set when -femit-dwarf-unwind is passed.
+ENUM_CODEGENOPT(EmitDwarfUnwind, llvm::EmitDwarfUnwindType, 2,
+                llvm::EmitDwarfUnwindType::Default)
+
 ///< Set when -fxray-always-emit-customevents is enabled.
 CODEGENOPT(XRayAlwaysEmitCustomEvents , 1, 0)
 

clang/include/clang/Driver/Options.td

@@ -3044,6 +3044,13 @@ def fmacro_prefix_map_EQ
 defm force_dwarf_frame : BoolFOption<"force-dwarf-frame",
   CodeGenOpts<"ForceDwarfFrameSection">, DefaultFalse,
   PosFlag<SetTrue, [CC1Option], "Always emit a debug frame section">, NegFlag<SetFalse>>;
+def femit_dwarf_unwind_EQ : Joined<["-"], "femit-dwarf-unwind=">,
+  Group<f_Group>, Flags<[CC1Option, CC1AsOption]>,
+  HelpText<"When to emit DWARF unwind (EH frame) info">,
+  Values<"always,no-compact-unwind,default">,
+  NormalizedValues<["Always", "NoCompactUnwind", "Default"]>,
+  NormalizedValuesScope<"llvm::EmitDwarfUnwindType">,
+  MarshallingInfoEnum<CodeGenOpts<"EmitDwarfUnwind">, "Default">;
 def g_Flag : Flag<["-"], "g">, Group<g_Group>,
   HelpText<"Generate source-level debug information">;
 def gline_tables_only : Flag<["-"], "gline-tables-only">, Group<gN_Group>,

clang/lib/CodeGen/BackendUtil.cpp

@@ -453,6 +453,7 @@ static bool initTargetOptions(DiagnosticsEngine &Diags,
   }
 
   Options.MCOptions.SplitDwarfFile = CodeGenOpts.SplitDwarfFile;
+  Options.MCOptions.EmitDwarfUnwind = CodeGenOpts.getEmitDwarfUnwind();
   Options.MCOptions.MCRelaxAll = CodeGenOpts.RelaxAll;
   Options.MCOptions.MCSaveTempLabels = CodeGenOpts.SaveTempLabels;
   Options.MCOptions.MCUseDwarfDirectory =

clang/lib/Driver/ToolChains/Clang.cpp

@@ -2518,6 +2518,8 @@ static void CollectArgsForIntegratedAssembler(Compilation &C,
                    DefaultIncrementalLinkerCompatible))
     CmdArgs.push_back("-mincremental-linker-compatible");
 
+  Args.AddLastArg(CmdArgs, options::OPT_femit_dwarf_unwind_EQ);
+
   // If you add more args here, also add them to the block below that
   // starts with "// If CollectArgsForIntegratedAssembler() isn't called below".
 
@@ -4622,6 +4624,7 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
     }
     Args.ClaimAllArgs(options::OPT_Wa_COMMA);
     Args.ClaimAllArgs(options::OPT_Xassembler);
+    Args.ClaimAllArgs(options::OPT_femit_dwarf_unwind_EQ);
   }
 
   if (isa<AnalyzeJobAction>(JA)) {

clang/test/Driver/femit-dwarf-unwind.c

@@ -0,0 +1,14 @@
+// REQUIRES: x86-registered-target
+
+// RUN: rm -rf %t; mkdir %t
+// RUN: %clang -target x86_64-apple-macos11.0 -c %s -o %t/x86_64.o
+// RUN: %clang -target x86_64-apple-macos11.0 -femit-dwarf-unwind=no-compact-unwind -c %s -o %t/x86_64-no-dwarf.o
+// RUN: llvm-objdump --macho --dwarf=frames %t/x86_64.o | FileCheck %s --check-prefix=WITH-FDE
+// RUN: llvm-objdump --macho --dwarf=frames %t/x86_64-no-dwarf.o | FileCheck %s --check-prefix=NO-FDE
+
+// WITH-FDE: FDE
+// NO-FDE-NOT: FDE
+
+int foo() {
+  return 1;
+}

clang/test/Driver/femit-dwarf-unwind.s

@@ -0,0 +1,17 @@
+// REQUIRES: x86-registered-target
+
+// RUN: rm -rf %t; mkdir %t
+// RUN: %clang -target x86_64-apple-macos11.0 -c %s -o %t/x86_64.o
+// RUN: %clang -target x86_64-apple-macos11.0 -femit-dwarf-unwind=no-compact-unwind -c %s -o %t/x86_64-no-dwarf.o
+// RUN: llvm-objdump --macho --dwarf=frames %t/x86_64.o | FileCheck %s --check-prefix=WITH-FDE
+// RUN: llvm-objdump --macho --dwarf=frames %t/x86_64-no-dwarf.o | FileCheck %s --check-prefix=NO-FDE
+
+// WITH-FDE: FDE
+// NO-FDE-NOT: FDE
+
+.text
+_foo:
+  .cfi_startproc
+  .cfi_def_cfa_offset 8
+  ret
+  .cfi_endproc

clang/tools/driver/cc1as_main.cpp

@@ -137,6 +137,9 @@ struct AssemblerInvocation {
   unsigned IncrementalLinkerCompatible : 1;
   unsigned EmbedBitcode : 1;
 
+  /// Whether to emit DWARF unwind info.
+  EmitDwarfUnwindType EmitDwarfUnwind;
+
   /// The name of the relocation model to use.
   std::string RelocationModel;
 
@@ -317,6 +320,14 @@ bool AssemblerInvocation::CreateFromArgs(AssemblerInvocation &Opts,
                             .Default(0);
   }
 
+  if (auto *A = Args.getLastArg(OPT_femit_dwarf_unwind_EQ)) {
+    Opts.EmitDwarfUnwind =
+        llvm::StringSwitch<EmitDwarfUnwindType>(A->getValue())
+            .Case("always", EmitDwarfUnwindType::Always)
+            .Case("no-compact-unwind", EmitDwarfUnwindType::NoCompactUnwind)
+            .Case("default", EmitDwarfUnwindType::Default);
+  }
+
   return Success;
 }
 
@@ -367,6 +378,8 @@ static bool ExecuteAssemblerImpl(AssemblerInvocation &Opts,
   assert(MRI && "Unable to create target register info!");
 
   MCTargetOptions MCOptions;
+  MCOptions.EmitDwarfUnwind = Opts.EmitDwarfUnwind;
+
   std::unique_ptr<MCAsmInfo> MAI(
       TheTarget->createMCAsmInfo(*MRI, Opts.Triple, MCOptions));
   assert(MAI && "Unable to create target asm info!");

llvm/include/llvm/MC/MCContext.h

@@ -67,6 +67,7 @@ template <typename T> class SmallVectorImpl;
 class SMDiagnostic;
 class SMLoc;
 class SourceMgr;
+enum class EmitDwarfUnwindType;
 
 /// Context object for machine code objects.  This class owns all of the
 /// sections that it creates.
@@ -772,6 +773,7 @@ public:
   bool getGenDwarfForAssembly() { return GenDwarfForAssembly; }
   void setGenDwarfForAssembly(bool Value) { GenDwarfForAssembly = Value; }
   unsigned getGenDwarfFileNumber() { return GenDwarfFileNumber; }
+  EmitDwarfUnwindType emitDwarfUnwindInfo() const;
 
   void setGenDwarfFileNumber(unsigned FileNumber) {
     GenDwarfFileNumber = FileNumber;

llvm/include/llvm/MC/MCTargetOptions.h

@@ -31,6 +31,12 @@ enum class DebugCompressionType {
   Z,    ///< zlib style complession
 };
 
+enum class EmitDwarfUnwindType {
+  Always,          // Always emit dwarf unwind
+  NoCompactUnwind, // Only emit if compact unwind isn't available
+  Default,         // Default behavior is based on the target
+};
+
 class StringRef;
 
 class MCTargetOptions {
@@ -56,6 +62,9 @@ public:
   bool PreserveAsmComments : 1;
 
   bool Dwarf64 : 1;
+
+  EmitDwarfUnwindType EmitDwarfUnwind;
+
   int DwarfVersion = 0;
 
   enum DwarfDirectory {

llvm/include/llvm/MC/MCTargetOptionsCommandFlags.h

@@ -20,6 +20,7 @@
 namespace llvm {
 
 class MCTargetOptions;
+enum class EmitDwarfUnwindType;
 
 namespace mc {
 
@@ -32,6 +33,8 @@ int getDwarfVersion();
 
 bool getDwarf64();
 
+EmitDwarfUnwindType getEmitDwarfUnwind();
+
 bool getShowMCInst();
 
 bool getFatalWarnings();

llvm/lib/CodeGen/LLVMTargetMachine.cpp

@@ -264,6 +264,9 @@ bool LLVMTargetMachine::addPassesToEmitMC(PassManagerBase &PM, MCContext *&Ctx,
          "Cannot emit MC with limited codegen pipeline");
 
   Ctx = &MMIWP->getMMI().getContext();
+  // libunwind is unable to load compact unwind dynamically, so we must generate
+  // DWARF unwind info for the JIT.
+  Options.MCOptions.EmitDwarfUnwind = EmitDwarfUnwindType::Always;
   if (Options.MCOptions.MCSaveTempLabels)
     Ctx->setAllowTemporaryLabels(false);
 

llvm/lib/CodeGen/MachineModuleInfo.cpp

@@ -60,7 +60,7 @@ MachineModuleInfo::MachineModuleInfo(MachineModuleInfo &&MMI)
     : TM(std::move(MMI.TM)),
       Context(MMI.TM.getTargetTriple(), MMI.TM.getMCAsmInfo(),
               MMI.TM.getMCRegisterInfo(), MMI.TM.getMCSubtargetInfo(), nullptr,
-              nullptr, false),
+              &MMI.TM.Options.MCOptions, false),
       MachineFunctions(std::move(MMI.MachineFunctions)) {
   Context.setObjectFileInfo(MMI.TM.getObjFileLowering());
   ObjFileMMI = MMI.ObjFileMMI;
@@ -72,7 +72,7 @@ MachineModuleInfo::MachineModuleInfo(MachineModuleInfo &&MMI)
 MachineModuleInfo::MachineModuleInfo(const LLVMTargetMachine *TM)
     : TM(*TM), Context(TM->getTargetTriple(), TM->getMCAsmInfo(),
                        TM->getMCRegisterInfo(), TM->getMCSubtargetInfo(),
-                       nullptr, nullptr, false) {
+                       nullptr, &TM->Options.MCOptions, false) {
   Context.setObjectFileInfo(TM->getObjFileLowering());
   initialize();
 }
@@ -81,7 +81,7 @@ MachineModuleInfo::MachineModuleInfo(const LLVMTargetMachine *TM,
                                      MCContext *ExtContext)
     : TM(*TM), Context(TM->getTargetTriple(), TM->getMCAsmInfo(),
                        TM->getMCRegisterInfo(), TM->getMCSubtargetInfo(),
-                       nullptr, nullptr, false),
+                       nullptr, &TM->Options.MCOptions, false),
       ExternalContext(ExtContext) {
   Context.setObjectFileInfo(TM->getObjFileLowering());
   initialize();

llvm/lib/ExecutionEngine/MCJIT/MCJIT.cpp

@@ -19,6 +19,7 @@
 #include "llvm/IR/LegacyPassManager.h"
 #include "llvm/IR/Mangler.h"
 #include "llvm/IR/Module.h"
+#include "llvm/MC/MCContext.h"
 #include "llvm/Object/Archive.h"
 #include "llvm/Object/ObjectFile.h"
 #include "llvm/Support/DynamicLibrary.h"

llvm/lib/ExecutionEngine/Orc/CompileUtils.cpp

@@ -12,6 +12,7 @@
 #include "llvm/ExecutionEngine/ObjectCache.h"
 #include "llvm/IR/LegacyPassManager.h"
 #include "llvm/IR/Module.h"
+#include "llvm/MC/MCContext.h"
 #include "llvm/Object/ObjectFile.h"
 #include "llvm/Support/Error.h"
 #include "llvm/Support/ErrorHandling.h"

llvm/lib/ExecutionEngine/RuntimeDyld/RTDyldMemoryManager.cpp

@@ -95,18 +95,16 @@ void RTDyldMemoryManager::registerEHFramesInProcess(uint8_t *Addr,
   // and projects/libunwind/src/UnwindLevel1-gcc-ext.c.
   const char *P = (const char *)Addr;
   const char *End = P + Size;
-  do  {
+  while (P != End)
     P = processFDE(P, false);
-  } while(P != End);
 }
 
 void RTDyldMemoryManager::deregisterEHFramesInProcess(uint8_t *Addr,
                                                       size_t Size) {
   const char *P = (const char *)Addr;
   const char *End = P + Size;
-  do  {
+  while (P != End)
     P = processFDE(P, true);
-  } while(P != End);
 }
 
 #else

llvm/lib/MC/MCContext.cpp

@@ -877,6 +877,12 @@ void MCContext::RemapDebugPaths() {
 // Dwarf Management
 //===----------------------------------------------------------------------===//
 
+EmitDwarfUnwindType MCContext::emitDwarfUnwindInfo() const {
+  if (!TargetOptions)
+    return EmitDwarfUnwindType::Default;
+  return TargetOptions->EmitDwarfUnwind;
+}
+
 void MCContext::setGenDwarfRootFile(StringRef InputFileName, StringRef Buffer) {
   // MCDwarf needs the root file as well as the compilation directory.
   // If we find a '.file 0' directive that will supersede these values.

llvm/lib/MC/MCDwarf.cpp

@@ -1842,8 +1842,6 @@ template <> struct DenseMapInfo<CIEKey> {
 
 void MCDwarfFrameEmitter::Emit(MCObjectStreamer &Streamer, MCAsmBackend *MAB,
                                bool IsEH) {
-  Streamer.generateCompactUnwindEncodings(MAB);
-
   MCContext &Context = Streamer.getContext();
   const MCObjectFileInfo *MOFI = Context.getObjectFileInfo();
   const MCAsmInfo *AsmInfo = Context.getAsmInfo();
@@ -1853,6 +1851,7 @@ void MCDwarfFrameEmitter::Emit(MCObjectStreamer &Streamer, MCAsmBackend *MAB,
   // Emit the compact unwind info if available.
   bool NeedsEHFrameSection = !MOFI->getSupportsCompactUnwindWithoutEHFrame();
   if (IsEH && MOFI->getCompactUnwindSection()) {
+    Streamer.generateCompactUnwindEncodings(MAB);
     bool SectionEmitted = false;
     for (const MCDwarfFrameInfo &Frame : FrameArray) {
       if (Frame.CompactUnwindEncoding == 0) continue;

llvm/lib/MC/MCObjectFileInfo.cpp

@@ -64,8 +64,18 @@ void MCObjectFileInfo::initMachOMCObjectFileInfo(const Triple &T) {
       (T.getArch() == Triple::aarch64 || T.getArch() == Triple::aarch64_32))
     SupportsCompactUnwindWithoutEHFrame = true;
 
-  if (T.isWatchABI())
+  switch (Ctx->emitDwarfUnwindInfo()) {
+  case EmitDwarfUnwindType::Always:
+    OmitDwarfIfHaveCompactUnwind = false;
+    break;
+  case EmitDwarfUnwindType::NoCompactUnwind:
     OmitDwarfIfHaveCompactUnwind = true;
+    break;
+  case EmitDwarfUnwindType::Default:
+    OmitDwarfIfHaveCompactUnwind =
+        T.isWatchABI() || SupportsCompactUnwindWithoutEHFrame;
+    break;
+  }
 
   FDECFIEncoding = dwarf::DW_EH_PE_pcrel;
 

llvm/lib/MC/MCTargetOptions.cpp

@@ -17,6 +17,7 @@ MCTargetOptions::MCTargetOptions()
       MCSaveTempLabels(false), MCIncrementalLinkerCompatible(false),
       ShowMCEncoding(false), ShowMCInst(false), AsmVerbose(false),
       PreserveAsmComments(true), Dwarf64(false),
+      EmitDwarfUnwind(EmitDwarfUnwindType::Default),
       MCUseDwarfDirectory(DefaultDwarfDirectory) {}
 
 StringRef MCTargetOptions::getABIName() const {

llvm/lib/MC/MCTargetOptionsCommandFlags.cpp

@@ -1,5 +1,4 @@
-//===-- MCTargetOptionsCommandFlags.cpp --------------------------*- C++
+//===-- MCTargetOptionsCommandFlags.cpp -----------------------*- C++ //-*-===//
-//-*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -39,6 +38,7 @@ MCOPT_EXP(bool, RelaxAll)
 MCOPT(bool, IncrementalLinkerCompatible)
 MCOPT(int, DwarfVersion)
 MCOPT(bool, Dwarf64)
+MCOPT(EmitDwarfUnwindType, EmitDwarfUnwind)
 MCOPT(bool, ShowMCInst)
 MCOPT(bool, FatalWarnings)
 MCOPT(bool, NoWarn)
@@ -73,6 +73,19 @@ llvm::mc::RegisterMCTargetOptionsFlags::RegisterMCTargetOptionsFlags() {
       cl::desc("Generate debugging info in the 64-bit DWARF format"));
   MCBINDOPT(Dwarf64);
 
+  static cl::opt<EmitDwarfUnwindType> EmitDwarfUnwind(
+      "emit-dwarf-unwind", cl::desc("Whether to emit DWARF EH frame entries."),
+      cl::init(EmitDwarfUnwindType::Default),
+      cl::values(clEnumValN(EmitDwarfUnwindType::Always, "always",
+                            "Always emit EH frame entries"),
+                 clEnumValN(EmitDwarfUnwindType::NoCompactUnwind,
+                            "no-compact-unwind",
+                            "Only emit EH frame entries when compact unwind is "
+                            "not available"),
+                 clEnumValN(EmitDwarfUnwindType::Default, "default",
+                            "Use target platform default")));
+  MCBINDOPT(EmitDwarfUnwind);
+
   static cl::opt<bool> ShowMCInst(
       "asm-show-inst",
       cl::desc("Emit internal instruction representation to assembly file"));
@@ -116,5 +129,7 @@ MCTargetOptions llvm::mc::InitMCTargetOptionsFromFlags() {
   Options.MCNoWarn = getNoWarn();
   Options.MCNoDeprecatedWarn = getNoDeprecatedWarn();
   Options.MCNoTypeCheck = getNoTypeCheck();
+  Options.EmitDwarfUnwind = getEmitDwarfUnwind();
+
   return Options;
 }

llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp

@@ -1377,7 +1377,7 @@ public:
       default:
         // Any other CFI directives indicate a frame that we aren't prepared
         // to represent via compact unwind, so just bail out.
-        return 0;
+        return CU::UNWIND_MODE_DWARF;
       case MCCFIInstruction::OpDefCfaRegister: {
         // Defines a frame pointer. E.g.
         //
@@ -1391,7 +1391,7 @@ public:
         // generate a compact unwinding representation, so bail out.
         if (*MRI.getLLVMRegNum(Inst.getRegister(), true) !=
             (Is64Bit ? X86::RBP : X86::EBP))
-          return 0;
+          return CU::UNWIND_MODE_DWARF;
 
         // Reset the counts.
         memset(SavedRegs, 0, sizeof(SavedRegs));

llvm/test/MC/MachO/AArch64/emit-dwarf-unwind.s

@@ -0,0 +1,33 @@
+// RUN: rm -rf %t; mkdir %t
+// RUN: llvm-mc -triple x86_64-apple-macos11.0 %s -filetype=obj -o %t/x86_64.o
+// RUN: llvm-objdump --macho --dwarf=frames %t/x86_64.o | FileCheck %s --check-prefix TWO-FDES
+// RUN: llvm-mc -triple arm64-apple-macos11.0 %s -filetype=obj -o %t/arm64.o
+// RUN: llvm-objdump --macho --dwarf=frames %t/arm64.o | FileCheck %s --check-prefix ONE-FDE
+// RUN: llvm-mc -triple x86_64-apple-macos11.0 %s -filetype=obj --emit-dwarf-unwind no-compact-unwind -o %t/x86_64-no-dwarf.o
+// RUN: llvm-objdump --macho --dwarf=frames %t/x86_64-no-dwarf.o | FileCheck %s --check-prefix ONE-FDE
+// RUN: llvm-mc -triple arm64-apple-macos11.0 %s -filetype=obj --emit-dwarf-unwind always -o %t/arm64-dwarf.o
+// RUN: llvm-objdump --macho --dwarf=frames %t/arm64-dwarf.o | FileCheck %s --check-prefix TWO-FDES
+
+// TWO-FDES: FDE
+// TWO-FDES: FDE
+
+// ONE-FDE-NOT: FDE
+// ONE-FDE:     FDE
+// ONE-FDE-NOT: FDE
+
+_main:
+  .cfi_startproc
+  .cfi_def_cfa_offset 16
+  ret
+  .cfi_endproc
+
+_foo:
+  .cfi_startproc
+  .cfi_def_cfa_offset 16
+  /// This encodes DW_CFA_GNU_args_size which cannot be expressed using compact
+  /// unwind, so we must use DWARf unwind for this function.
+  .cfi_escape 0x2e, 0x10
+  ret
+  .cfi_endproc
+
+.subsections_via_symbols

llvm/test/MC/X86/compact-unwind-mode-dwarf.s

@@ -0,0 +1,50 @@
+// RUN: llvm-mc -triple x86_64-apple-macos10.6 -filetype=obj %s -o %t.o
+// RUN: llvm-objdump --macho --unwind-info --dwarf=frames %t.o | FileCheck %s
+
+/// For functions whose unwind info cannot be encoded with compact unwind, make
+/// sure that we encode them using DWARF unwind, and make sure we emit a compact
+/// unwind entry that indicates that a DWARF encoding is being used.
+
+_f:
+  .cfi_startproc
+  ## This encodes DW_CFA_GNU_args_size which cannot be expressed using compact
+  ## unwind, so we must use DWARF unwind instead.
+  .cfi_escape 0x2e, 0x10
+  ret
+  .cfi_endproc
+
+_g:
+  .cfi_startproc
+  ## This encodes DW_CFA_GNU_args_size which cannot be expressed using compact
+  ## unwind, so we must use DWARF unwind instead.
+  .cfi_escape 0x2e, 0x10
+  ret
+  .cfi_endproc
+
+// CHECK: Contents of __compact_unwind section:
+// CHECK:   Entry at offset 0x0:
+// CHECK:     start:                0x[[#%x,F:]] _f
+// CHECK:     length:               0x1
+// CHECK:     compact encoding:     0x04000000
+// CHECK:   Entry at offset 0x20:
+// CHECK:     start:                0x[[#%x,G:]] _g
+// CHECK:     length:               0x1
+// CHECK:     compact encoding:     0x04000000
+
+// CHECK: .eh_frame contents:
+// CHECK: 00000000 00000014 00000000 CIE
+// CHECK:   Format:                DWARF32
+// CHECK:   Version:               1
+// CHECK:   Augmentation:          "zR"
+// CHECK:   Code alignment factor: 1
+// CHECK:   Data alignment factor: -8
+// CHECK:   Return address column: 16
+// CHECK:   Augmentation data:     10
+
+// CHECK: FDE cie=00000000 pc=[[#%.8x,F]]...
+// CHECK:   Format:       DWARF32
+// CHECK:   DW_CFA_GNU_args_size: +16
+
+// CHECK: FDE cie=00000000 pc=[[#%.8x,G]]...
+// CHECK:   Format:       DWARF32
+// CHECK:   DW_CFA_GNU_args_size: +16