[MC] Remove unnecessary DWARFMustBeAtTheEnd check

MaskRay · MaskRay · commit aa86f4f18549 · 2024-07-20T10:43:52.000-07:00
36a15cb introduced the DWARFMustBeAtTheEnd check to ensure DWARF sections were placed after all text sections to help avoid out-of-range branches for Darwin ARM. The commit removed a Darwin ARM hack from 20e5f5e (2009), likely due to a no-longer-relevant assembler limitation. However, this check is no longer relevant due to the following: * Our CodeGen approach reliably places DWARF sections at the end. * Darwin AArch32 is less relevant today. Removing this check also addresses a minor clang cc1as crash that could occur when text sections were placed after DWARF sections (e9ad54b (2015)).
diff --git a/llvm/include/llvm/MC/TargetRegistry.h b/llvm/include/llvm/MC/TargetRegistry.h
@@ -201,8 +201,7 @@ class Target {
   using MachOStreamerCtorTy =
       MCStreamer *(*)(MCContext &Ctx, std::unique_ptr<MCAsmBackend> &&TAB,
                       std::unique_ptr<MCObjectWriter> &&OW,
-                      std::unique_ptr<MCCodeEmitter> &&Emitter,
-                      bool DWARFMustBeAtTheEnd);
+                      std::unique_ptr<MCCodeEmitter> &&Emitter);
   using COFFStreamerCtorTy =
       MCStreamer *(*)(MCContext &Ctx, std::unique_ptr<MCAsmBackend> &&TAB,
                       std::unique_ptr<MCObjectWriter> &&OW,
@@ -559,7 +558,7 @@ class Target {
                                      std::unique_ptr<MCObjectWriter> &&OW,
                                      std::unique_ptr<MCCodeEmitter> &&Emitter,
                                      const MCSubtargetInfo &STI, bool, bool,
-                                     bool DWARFMustBeAtTheEnd) const {
+                                     bool) const {
     MCStreamer *S = nullptr;
     switch (T.getObjectFormat()) {
     case Triple::UnknownObjectFormat:
@@ -573,10 +572,10 @@ class Target {
     case Triple::MachO:
       if (MachOStreamerCtorFn)
         S = MachOStreamerCtorFn(Ctx, std::move(TAB), std::move(OW),
-                                std::move(Emitter), DWARFMustBeAtTheEnd);
+                                std::move(Emitter));
       else
         S = createMachOStreamer(Ctx, std::move(TAB), std::move(OW),
-                                std::move(Emitter), DWARFMustBeAtTheEnd);
+                                std::move(Emitter), false);
       break;
     case Triple::ELF:
       if (ELFStreamerCtorFn)
diff --git a/llvm/lib/CodeGen/LLVMTargetMachine.cpp b/llvm/lib/CodeGen/LLVMTargetMachine.cpp
@@ -208,9 +208,8 @@ Expected<std::unique_ptr<MCStreamer>> LLVMTargetMachine::createMCStreamer(
         T, Context, std::unique_ptr<MCAsmBackend>(MAB),
         DwoOut ? MAB->createDwoObjectWriter(Out, *DwoOut)
                : MAB->createObjectWriter(Out),
-        std::unique_ptr<MCCodeEmitter>(MCE), STI, Options.MCOptions.MCRelaxAll,
-        Options.MCOptions.MCIncrementalLinkerCompatible,
-        /*DWARFMustBeAtTheEnd*/ true));
+        std::unique_ptr<MCCodeEmitter>(MCE), STI, /*ignore=*/false, false,
+        false));
     break;
   }
   case CodeGenFileType::Null:
@@ -284,9 +283,7 @@ bool LLVMTargetMachine::addPassesToEmitMC(PassManagerBase &PM, MCContext *&Ctx,
   const Triple &T = getTargetTriple();
   std::unique_ptr<MCStreamer> AsmStreamer(getTarget().createMCObjectStreamer(
       T, *Ctx, std::move(MAB), MAB->createObjectWriter(Out), std::move(MCE),
-      STI, Options.MCOptions.MCRelaxAll,
-      Options.MCOptions.MCIncrementalLinkerCompatible,
-      /*DWARFMustBeAtTheEnd*/ true));
+      STI, /*ignore=*/false, false, false));
 
   // Create the AsmPrinter, which takes ownership of AsmStreamer if successful.
   FunctionPass *Printer =
diff --git a/llvm/lib/MC/MCMachOStreamer.cpp b/llvm/lib/MC/MCMachOStreamer.cpp
@@ -54,9 +54,6 @@ class MCMachOStreamer : public MCObjectStreamer {
   /// need for local relocations. False by default.
   bool LabelSections;
 
-  bool DWARFMustBeAtTheEnd;
-  bool CreatedADWARFSection;
-
   /// HasSectionLabel - map of which sections have already had a non-local
   /// label emitted to them. Used so we don't emit extraneous linker local
   /// labels in the middle of the section.
@@ -70,16 +67,13 @@ class MCMachOStreamer : public MCObjectStreamer {
 public:
   MCMachOStreamer(MCContext &Context, std::unique_ptr<MCAsmBackend> MAB,
                   std::unique_ptr<MCObjectWriter> OW,
-                  std::unique_ptr<MCCodeEmitter> Emitter,
-                  bool DWARFMustBeAtTheEnd, bool label)
+                  std::unique_ptr<MCCodeEmitter> Emitter, bool label)
       : MCObjectStreamer(Context, std::move(MAB), std::move(OW),
                          std::move(Emitter)),
-        LabelSections(label), DWARFMustBeAtTheEnd(DWARFMustBeAtTheEnd),
-        CreatedADWARFSection(false) {}
+        LabelSections(label) {}
 
   /// state management
   void reset() override {
-    CreatedADWARFSection = false;
     HasSectionLabel.clear();
     MCObjectStreamer::reset();
   }
@@ -141,48 +135,9 @@ class MCMachOStreamer : public MCObjectStreamer {
 
 } // end anonymous namespace.
 
-static bool canGoAfterDWARF(const MCSectionMachO &MSec) {
-  // These sections are created by the assembler itself after the end of
-  // the .s file.
-  StringRef SegName = MSec.getSegmentName();
-  StringRef SecName = MSec.getName();
-
-  if (SegName == "__LD" && SecName == "__compact_unwind")
-    return true;
-
-  if (SegName == "__IMPORT") {
-    if (SecName == "__jump_table")
-      return true;
-
-    if (SecName == "__pointers")
-      return true;
-  }
-
-  if (SegName == "__TEXT" && SecName == "__eh_frame")
-    return true;
-
-  if (SegName == "__DATA" &&
-      (SecName == "__llvm_addrsig" || SecName == "__nl_symbol_ptr" ||
-       SecName == "__thread_ptr"))
-    return true;
-  if (SegName == "__LLVM" && (SecName == "__cg_profile"))
-    return true;
-
-  if (SegName == "__DATA" && SecName == "__auth_ptr")
-    return true;
-
-  return false;
-}
-
 void MCMachOStreamer::changeSection(MCSection *Section, uint32_t Subsection) {
   // Change the section normally.
-  bool Created = changeSectionImpl(Section, Subsection);
-  const MCSectionMachO &MSec = *cast<MCSectionMachO>(Section);
-  StringRef SegName = MSec.getSegmentName();
-  if (SegName == "__DWARF")
-    CreatedADWARFSection = true;
-  else if (Created && DWARFMustBeAtTheEnd && !canGoAfterDWARF(MSec))
-    assert(!CreatedADWARFSection && "Creating regular section after DWARF");
+  changeSectionImpl(Section, Subsection);
 
   // Output a linker-local symbol so we don't need section-relative local
   // relocations. The linker hates us when we do that.
@@ -576,9 +531,8 @@ MCStreamer *llvm::createMachOStreamer(MCContext &Context,
                                       std::unique_ptr<MCCodeEmitter> &&CE,
                                       bool DWARFMustBeAtTheEnd,
                                       bool LabelSections) {
-  MCMachOStreamer *S =
-      new MCMachOStreamer(Context, std::move(MAB), std::move(OW), std::move(CE),
-                          DWARFMustBeAtTheEnd, LabelSections);
+  MCMachOStreamer *S = new MCMachOStreamer(
+      Context, std::move(MAB), std::move(OW), std::move(CE), LabelSections);
   const Triple &Target = Context.getTargetTriple();
   S->emitVersionForTarget(
       Target, Context.getObjectFileInfo()->getSDKVersion(),
diff --git a/llvm/lib/Target/AArch64/MCTargetDesc/AArch64MCTargetDesc.cpp b/llvm/lib/Target/AArch64/MCTargetDesc/AArch64MCTargetDesc.cpp
@@ -386,13 +386,12 @@ static MCStreamer *createELFStreamer(const Triple &T, MCContext &Ctx,
                                   std::move(Emitter));
 }
 
-static MCStreamer *createMachOStreamer(MCContext &Ctx,
-                                       std::unique_ptr<MCAsmBackend> &&TAB,
-                                       std::unique_ptr<MCObjectWriter> &&OW,
-                                       std::unique_ptr<MCCodeEmitter> &&Emitter,
-                                       bool DWARFMustBeAtTheEnd) {
+static MCStreamer *
+createMachOStreamer(MCContext &Ctx, std::unique_ptr<MCAsmBackend> &&TAB,
+                    std::unique_ptr<MCObjectWriter> &&OW,
+                    std::unique_ptr<MCCodeEmitter> &&Emitter) {
   return createMachOStreamer(Ctx, std::move(TAB), std::move(OW),
-                             std::move(Emitter), DWARFMustBeAtTheEnd,
+                             std::move(Emitter), /*ignore=*/false,
                              /*LabelSections*/ true);
 }
 
diff --git a/llvm/lib/Target/ARM/MCTargetDesc/ARMMCTargetDesc.cpp b/llvm/lib/Target/ARM/MCTargetDesc/ARMMCTargetDesc.cpp
@@ -369,10 +369,9 @@ static MCStreamer *createELFStreamer(const Triple &T, MCContext &Ctx,
 static MCStreamer *
 createARMMachOStreamer(MCContext &Ctx, std::unique_ptr<MCAsmBackend> &&MAB,
                        std::unique_ptr<MCObjectWriter> &&OW,
-                       std::unique_ptr<MCCodeEmitter> &&Emitter,
-                       bool DWARFMustBeAtTheEnd) {
+                       std::unique_ptr<MCCodeEmitter> &&Emitter) {
   return createMachOStreamer(Ctx, std::move(MAB), std::move(OW),
-                             std::move(Emitter), DWARFMustBeAtTheEnd);
+                             std::move(Emitter), false);
 }
 
 static MCInstPrinter *createARMMCInstPrinter(const Triple &T,
