[LiveDebugValues] 3/4 Add Xclang and CodeGen options for using instr-ref variable locations

[jmorse]

Summary

(Context: this thread http://lists.llvm.org/pipermail/llvm-dev/2020-June/142368.html )

This patch adds the -Xclang option "-fexperimental-debug-variable-locations" and same LLVM CodeGen option, to pick which variable location tracking solution to use.

Right now all the switch does is pick which LiveDebugValues implementation to use. Over time however, my aim is to add fragments of support in aid of this value-tracking RFC, also controlled by this command line switch. That will slowly move variable locations to be defined by an instruction calculating a value, and a DBG_INSTR_REF instruction referring to that value. Thus, this is going to grow into a "use the new kind of variable locations" switch, rather than just "use the new LiveDebugValues implementation".

[djtodoro]

Please add a test case for the Driver option (you can take a look into existing ones within clang/test/Driver/).

[jmorse]

(Rebase, only affecting LiveDebugValues.cpp)

[jmorse]

Add a test for the driver -Xclang option. As far as I understand this, we're just checking that the switch is accepted by the driver, not that it does anything in particular (please correct me if I'm wrong).

[djtodoro]

nit included, otherwise lgtm, thanks!

llvm/lib/CodeGen/LiveDebugValues/LiveDebugValues.cpp

45

is this clang-formatted?

clang/include/clang/Basic/CodeGenOptions.def

 /// Tune the debug info for this debugger.
 ENUM_CODEGENOPT(DebuggerTuning, llvm::DebuggerKind, 2,
                 llvm::DebuggerKind::Default)
 
 /// Dwarf version. Version zero indicates to LLVM that no DWARF should be
 /// emitted.
 VALUE_CODEGENOPT(DwarfVersion, 3, 0)
 
+/// Whether to use experimental new variable location tracking.
+CODEGENOPT(ValueTrackingVariableLocations, 1, 0)
+
 /// Whether we should emit CodeView debug information. It's possible to emit
 /// CodeView and DWARF into the same object.
 CODEGENOPT(EmitCodeView, 1, 0)
 
 /// Whether to emit the .debug$H section containing hashes of CodeView types.
 CODEGENOPT(CodeViewGHash, 1, 0)
 
 /// The kind of inlining to perform.

clang/include/clang/Driver/Options.td

def flto_visibility_public_std:
     HelpText<"Use public LTO visibility for classes in std and stdext namespaces">;
 def flto_unit: Flag<["-"], "flto-unit">,
     HelpText<"Emit IR to support LTO unit features (CFI, whole program vtable opt)">;
 def fno_lto_unit: Flag<["-"], "fno-lto-unit">;
 def fdebug_pass_manager : Flag<["-"], "fdebug-pass-manager">,
     HelpText<"Prints debug information for the new pass manager">;
 def fno_debug_pass_manager : Flag<["-"], "fno-debug-pass-manager">,
     HelpText<"Disables debug printing for the new pass manager">;
+def fexperimental_debug_variable_locations : Flag<["-"],
+    "fexperimental-debug-variable-locations">,
+    HelpText<"Use experimental new value-tracking variable locations">;
 // The driver option takes the key as a parameter to the -msign-return-address=
 // and -mbranch-protection= options, but CC1 has a separate option so we
 // don't have to parse the parameter twice.
 def msign_return_address_key_EQ : Joined<["-"], "msign-return-address-key=">,
     Values<"a_key,b_key">;
 def mbranch_target_enforce : Flag<["-"], "mbranch-target-enforce">;
 def fno_dllexport_inlines : Flag<["-"], "fno-dllexport-inlines">;
 def cfguard_no_checks : Flag<["-"], "cfguard-no-checks">,

clang/lib/CodeGen/BackendUtil.cpp

static void initTargetOptions(DiagnosticsEngine &Diags,
   Options.TLSSize = CodeGenOpts.TLSSize;
   Options.EmulatedTLS = CodeGenOpts.EmulatedTLS;
   Options.ExplicitEmulatedTLS = CodeGenOpts.ExplicitEmulatedTLS;
   Options.DebuggerTuning = CodeGenOpts.getDebuggerTuning();
   Options.EmitStackSizeSection = CodeGenOpts.StackSizeSection;
   Options.EmitAddrsig = CodeGenOpts.Addrsig;
   Options.ForceDwarfFrameSection = CodeGenOpts.ForceDwarfFrameSection;
   Options.EmitCallSiteInfo = CodeGenOpts.EmitCallSiteInfo;
+  Options.ValueTrackingVariableLocations =
+      CodeGenOpts.ValueTrackingVariableLocations;
   Options.XRayOmitFunctionIndex = CodeGenOpts.XRayOmitFunctionIndex;
 
   Options.MCOptions.SplitDwarfFile = CodeGenOpts.SplitDwarfFile;
   Options.MCOptions.MCRelaxAll = CodeGenOpts.RelaxAll;
   Options.MCOptions.MCSaveTempLabels = CodeGenOpts.SaveTempLabels;
   Options.MCOptions.MCUseDwarfDirectory = !CodeGenOpts.NoDwarfDirectoryAsm;
   Options.MCOptions.MCNoExecStack = CodeGenOpts.NoExecStack;
   Options.MCOptions.MCIncrementalLinkerCompatible =

clang/lib/Frontend/CompilerInvocation.cpp

const llvm::Triple::ArchType DebugEntryValueArchs[] = {
       llvm::Triple::arm, llvm::Triple::armeb, llvm::Triple::mips,
       llvm::Triple::mipsel, llvm::Triple::mips64, llvm::Triple::mips64el};
 
   llvm::Triple T(TargetOpts.Triple);
   if (Opts.OptimizationLevel > 0 && Opts.hasReducedDebugInfo() &&
       llvm::is_contained(DebugEntryValueArchs, T.getArch()))
     Opts.EmitCallSiteInfo = true;
 
+  Opts.ValueTrackingVariableLocations =
+      Args.hasArg(OPT_fexperimental_debug_variable_locations);
+
   Opts.DisableO0ImplyOptNone = Args.hasArg(OPT_disable_O0_optnone);
   Opts.DisableRedZone = Args.hasArg(OPT_disable_red_zone);
   Opts.IndirectTlsSegRefs = Args.hasArg(OPT_mno_tls_direct_seg_refs);
   Opts.ForbidGuardVariables = Args.hasArg(OPT_fforbid_guard_variables);
   Opts.UseRegisterSizedBitfieldAccess = Args.hasArg(
     OPT_fuse_register_sized_bitfield_access);
   Opts.RelaxedAliasing = Args.hasArg(OPT_relaxed_aliasing);
   Opts.StructPathTBAA = !Args.hasArg(OPT_no_struct_path_tbaa);

clang/test/Driver/debug-var-experimental-switch.c

+// RUN: %clang -Xclang -fexperimental-debug-variable-locations -fsyntax-only -disable-llvm-passes %s
+int main() {}

llvm/include/llvm/CodeGen/CommandFlags.h

 bool getEnableStackSizeSection();
 
 bool getEnableAddrsig();
 
 bool getEmitCallSiteInfo();
 
 bool getEnableDebugEntryValues();
 
+bool getValueTrackingVariableLocations();
+
 bool getForceDwarfFrameSection();
 
 bool getXRayOmitFunctionIndex();
 
 /// Create this object with static storage to register codegen-related command
 /// line options.
 struct RegisterCodeGenFlags {
   RegisterCodeGenFlags();

llvm/include/llvm/Target/TargetOptions.h

TargetOptions()
           DisableIntegratedAS(false), RelaxELFRelocations(false),
           FunctionSections(false), DataSections(false),
           UniqueSectionNames(true), UniqueBasicBlockSectionNames(false),
           TrapUnreachable(false), NoTrapAfterNoreturn(false), TLSSize(0),
           EmulatedTLS(false), ExplicitEmulatedTLS(false), EnableIPRA(false),
           EmitStackSizeSection(false), EnableMachineOutliner(false),
           SupportsDefaultOutlining(false), EmitAddrsig(false),
           EmitCallSiteInfo(false), SupportsDebugEntryValues(false),
-          EnableDebugEntryValues(false), ForceDwarfFrameSection(false),
-          XRayOmitFunctionIndex(false),
+          EnableDebugEntryValues(false), ValueTrackingVariableLocations(false),
+          ForceDwarfFrameSection(false), XRayOmitFunctionIndex(false),
           FPDenormalMode(DenormalMode::IEEE, DenormalMode::IEEE) {}
 
     /// DisableFramePointerElim - This returns true if frame pointer elimination
     /// optimization should be disabled for the given machine function.
     bool DisableFramePointerElim(const MachineFunction &MF) const;
 
     /// UnsafeFPMath - This flag is enabled when the
     /// -enable-unsafe-fp-math flag is specified on the command line.  When
public:
     /// of debug entry values even if the target does not officially support
     /// it. Useful for testing purposes only. This flag should never be checked
     /// directly, always use \ref ShouldEmitDebugEntryValues instead.
      unsigned EnableDebugEntryValues : 1;
     /// NOTE: There are targets that still do not support the debug entry values
     /// production.
     bool ShouldEmitDebugEntryValues() const;
 
+    // When set to true, use experimental new debug variable location tracking,
+    // which seeks to follow the values of variables rather than their location,
+    // post isel.
+    unsigned ValueTrackingVariableLocations : 1;
+
     /// Emit DWARF debug frame section.
     unsigned ForceDwarfFrameSection : 1;
 
     /// Emit XRay Function Index section
     unsigned XRayOmitFunctionIndex : 1;
 
     /// FloatABIType - This setting is set by -float-abi=xxx option is specfied
     /// on the command line. This setting may either be Default, Soft, or Hard.

llvm/lib/CodeGen/CommandFlags.cpp

 CGOPT(bool, UniqueSectionNames)
 CGOPT(bool, UniqueBasicBlockSectionNames)
 CGOPT(EABI, EABIVersion)
 CGOPT(DebuggerKind, DebuggerTuningOpt)
 CGOPT(bool, EnableStackSizeSection)
 CGOPT(bool, EnableAddrsig)
 CGOPT(bool, EmitCallSiteInfo)
 CGOPT(bool, EnableDebugEntryValues)
+CGOPT(bool, ValueTrackingVariableLocations)
 CGOPT(bool, ForceDwarfFrameSection)
 CGOPT(bool, XRayOmitFunctionIndex)
 
 codegen::RegisterCodeGenFlags::RegisterCodeGenFlags() {
 #define CGBINDOPT(NAME)                                                        \
   do {                                                                         \
     NAME##View = std::addressof(NAME);                                         \
   } while (0)
#define CGBINDOPT(NAME)                                                        \
   CGBINDOPT(EmitCallSiteInfo);
 
   static cl::opt<bool> EnableDebugEntryValues(
       "debug-entry-values",
       cl::desc("Enable debug info for the debug entry values."),
       cl::init(false));
   CGBINDOPT(EnableDebugEntryValues);
 
+  static cl::opt<bool> ValueTrackingVariableLocations(
+      "experimental-debug-variable-locations",
+      cl::desc("Use experimental new value-tracking variable locations"),
+      cl::init(false));
+  CGBINDOPT(ValueTrackingVariableLocations);
+
   static cl::opt<bool> ForceDwarfFrameSection(
       "force-dwarf-frame-section",
       cl::desc("Always emit a debug frame section."), cl::init(false));
   CGBINDOPT(ForceDwarfFrameSection);
 
   static cl::opt<bool> XRayOmitFunctionIndex(
       "no-xray-index", cl::desc("Don't emit xray_fn_idx section"),
       cl::init(false));
TargetOptions codegen::InitTargetOptionsFromCodeGenFlags() {
   Options.TLSSize = getTLSSize();
   Options.EmulatedTLS = getEmulatedTLS();
   Options.ExplicitEmulatedTLS = EmulatedTLSView->getNumOccurrences() > 0;
   Options.ExceptionModel = getExceptionModel();
   Options.EmitStackSizeSection = getEnableStackSizeSection();
   Options.EmitAddrsig = getEnableAddrsig();
   Options.EmitCallSiteInfo = getEmitCallSiteInfo();
   Options.EnableDebugEntryValues = getEnableDebugEntryValues();
+  Options.ValueTrackingVariableLocations = getValueTrackingVariableLocations();
   Options.ForceDwarfFrameSection = getForceDwarfFrameSection();
   Options.XRayOmitFunctionIndex = getXRayOmitFunctionIndex();
 
   Options.MCOptions = mc::InitMCTargetOptionsFromFlags();
 
   Options.ThreadModel = getThreadModel();
   Options.EABIVersion = getEABIVersion();
   Options.DebuggerTuning = getDebuggerTuningOpt();

llvm/lib/CodeGen/LiveDebugValues/LiveDebugValues.cpp

 //===- LiveDebugValues.cpp - Tracking Debug Value MIs ---------------------===//
 //
 // 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
 //
 //===----------------------------------------------------------------------===//
 
 #include "LiveDebugValues.h"
 
 #include "llvm/CodeGen/MachineBasicBlock.h"
 #include "llvm/CodeGen/MachineFrameInfo.h"
 #include "llvm/CodeGen/MachineFunctionPass.h"
 #include "llvm/CodeGen/Passes.h"
 #include "llvm/InitializePasses.h"
 #include "llvm/Pass.h"
+#include "llvm/Target/TargetMachine.h"
 
 /// \file LiveDebugValues.cpp
 ///
 /// The LiveDebugValues pass extends the range of variable locations
 /// (specified by DBG_VALUE instructions) from single blocks to successors
 /// and any other code locations where the variable location is valid.
 /// There are currently two implementations: the "VarLoc" implementation
 /// explicitly tracks the location of a variable, while the "InstrRef"

 /// Generic LiveDebugValues pass. Calls through to VarLocBasedLDV or
 /// InstrRefBasedLDV to perform location propagation, via the LDVImpl
 /// base class.
 class LiveDebugValues : public MachineFunctionPass {
 public:
   static char ID;
 
   LiveDebugValues();
-  ~LiveDebugValues() { delete TheImpl; }
+  ~LiveDebugValues() {
+    if (TheImpl)
+      delete TheImpl;
+  }
 
   /// Calculate the liveness information for the given machine function.
   bool runOnMachineFunction(MachineFunction &MF) override;
 
   MachineFunctionProperties getRequiredProperties() const override {
     return MachineFunctionProperties().set(
         MachineFunctionProperties::Property::NoVRegs);
   }
 
   void getAnalysisUsage(AnalysisUsage &AU) const override {
     AU.setPreservesCFG();
     MachineFunctionPass::getAnalysisUsage(AU);
   }
 
 private:
   LDVImpl *TheImpl;
+  TargetPassConfig *TPC;
 };
 
 char LiveDebugValues::ID = 0;
 
 char &llvm::LiveDebugValuesID = LiveDebugValues::ID;
 
 INITIALIZE_PASS(LiveDebugValues, DEBUG_TYPE, "Live DEBUG_VALUE analysis", false,
                 false)
 
 /// Default construct and initialize the pass.
 LiveDebugValues::LiveDebugValues() : MachineFunctionPass(ID) {
   initializeLiveDebugValuesPass(*PassRegistry::getPassRegistry());
-  TheImpl = llvm::makeVarLocBasedLiveDebugValues();
+  TheImpl = nullptr;
 }
 
 bool LiveDebugValues::runOnMachineFunction(MachineFunction &MF) {
-  auto *TPC = getAnalysisIfAvailable<TargetPassConfig>();
+  if (!TheImpl) {
+    TPC = getAnalysisIfAvailable<TargetPassConfig>();
+
+    bool InstrRefBased = false;
+    if (TPC) {
+      auto &TM = TPC->getTM<TargetMachine>();
+      InstrRefBased = TM.Options.ValueTrackingVariableLocations;
+    }
+
+    if (InstrRefBased)
+      TheImpl = llvm::makeInstrRefBasedLiveDebugValues();
+    else
+      TheImpl = llvm::makeVarLocBasedLiveDebugValues();
+  }
+
   return TheImpl->ExtendRanges(MF, TPC);
 }