AsmPrinter: Emit debug information sections lasst

[MatzeB]

Summary

Attaching debug information should ideally not change the rest of the
binary. This works best when the debug information sections come last in
the file. See also the discussion in https://reviews.llvm.org/D29315 or
r197922 or rdar://15623193

This means that we should output the debug information after calling the
targets EmitEndOfAsmFile.

@rafael: Could you please look at the changes to test/DebugInfo/X86/arange-and-stub.ll. This patch moves ".section .data.DW.ref.foo,"aGw",@progbits,DW.ref.foo,comdat" from the end of the file to before the debug info which "CHECK: .data" catches unitentionally I think.

[aprantl]

include/llvm/CodeGen/AsmPrinter.h

129

Is this supposed to mean "(The) Handler's" or "Handles", or can I just not parse that sentence? ;-)

lib/CodeGen/AsmPrinter/AsmPrinter.cpp

257

enum or /*EmitLate=*/ ?

[MatzeB]

include/llvm/CodeGen/AsmPrinter.h

129

Yep I meant "The Handler's" and tried hard to stay within 80 columns, looks like I need a line break after all :)

[echristo]

include/llvm/CodeGen/AsmPrinter.h

129

Let's try to avoid booleans here and define an enum of "when to emit" at least?

lib/CodeGen/AsmPrinter/AsmPrinter.cpp

1204

This loop makes it feel like we should actually be checking EH for "emit early" rather than everything else for emit late...

1285

Unconvinced that this should go after EmitEndOfAsmFile... what's the rationale here?

1292

Comment as to why this isn't next to the endModule above.

include/llvm/CodeGen/AsmPrinter.h

private:
   MachineLoopInfo *LI;
 
   struct HandlerInfo {
     AsmPrinterHandler *Handler;
     const char *TimerName;
     const char *TimerDescription;
     const char *TimerGroupName;
     const char *TimerGroupDescription;
+    bool EmitLate; ///< Handlers endModule() is called after EmitEndOfAsmFile().
     HandlerInfo(AsmPrinterHandler *Handler, const char *TimerName,
                 const char *TimerDescription, const char *TimerGroupName,
-                const char *TimerGroupDescription)
+                const char *TimerGroupDescription, bool EmitLate = false)
         : Handler(Handler), TimerName(TimerName),
           TimerDescription(TimerDescription), TimerGroupName(TimerGroupName),
-          TimerGroupDescription(TimerGroupDescription) {}
+          TimerGroupDescription(TimerGroupDescription), EmitLate(EmitLate) {}
   };
   /// A vector of all debug/EH info emitters we should use. This vector
   /// maintains ownership of the emitters.
   SmallVector<HandlerInfo, 2> Handlers;
 
   /// If the target supports dwarf debug info, this pointer is non-null.
   DwarfDebug *DD;
 

lib/CodeGen/AsmPrinter/AsmPrinter.cpp

bool AsmPrinter::doInitialization(Module &M) {
 
   if (MAI->doesSupportDebugInformation()) {
     bool EmitCodeView = MMI->getModule()->getCodeViewFlag();
     if (EmitCodeView && (TM.getTargetTriple().isKnownWindowsMSVCEnvironment() ||
                          TM.getTargetTriple().isWindowsItaniumEnvironment())) {
       Handlers.push_back(HandlerInfo(new CodeViewDebug(this),
                                      DbgTimerName, DbgTimerDescription,
                                      CodeViewLineTablesGroupName,
-                                     CodeViewLineTablesGroupDescription));
+                                     CodeViewLineTablesGroupDescription, true));
     }
     if (!EmitCodeView || MMI->getModule()->getDwarfVersion()) {
       DD = new DwarfDebug(this, &M);
       DD->beginModule();
       Handlers.push_back(HandlerInfo(DD, DbgTimerName, DbgTimerDescription,
-                                     DWARFGroupName, DWARFGroupDescription));
+                                     DWARFGroupName, DWARFGroupDescription,
+                                     true));
     }
   }
 
   switch (MAI->getExceptionHandlingType()) {
   case ExceptionHandling::SjLj:
   case ExceptionHandling::DwarfCFI:
   case ExceptionHandling::ARM:
     isCFIMoveForDebugging = true;
if (!Stubs.empty()) {
       for (const auto &Stub : Stubs) {
         OutStreamer->EmitLabel(Stub.first);
         OutStreamer->EmitSymbolValue(Stub.second.getPointer(),
                                      DL.getPointerSize());
       }
     }
   }
 
-  // Finalize debug and EH information.
+  // Called endModule on handlers (exception info).
   for (const HandlerInfo &HI : Handlers) {
+    if (HI.EmitLate)
+      continue;
     NamedRegionTimer T(HI.TimerName, HI.TimerDescription, HI.TimerGroupName,
                        HI.TimerGroupDescription, TimePassesIsEnabled);
     HI.Handler->endModule();
-    delete HI.Handler;
   }
-  Handlers.clear();
-  DD = nullptr;
 
   // If the target wants to know about weak references, print them all.
   if (MAI->getWeakRefDirective()) {
     // FIXME: This is not lazy, it would be nice to only print weak references
     // to stuff that is actually used.  Note that doing so would require targets
     // to notice uses in operands (due to constant exprs etc).  This should
     // happen with the MC stuff eventually.
 
bool AsmPrinter::doFinalization(Module &M) {
   if (!InitTrampolineIntrinsic || InitTrampolineIntrinsic->use_empty())
     if (MCSection *S = MAI->getNonexecutableStackSection(OutContext))
       OutStreamer->SwitchSection(S);
 
   // Allow the target to emit any magic that it wants at the end of the file,
   // after everything else has gone out.
   EmitEndOfAsmFile(M);
 
+  // Finalize late handlers (debug info).
+  for (const HandlerInfo &HI : Handlers) {
+    if (HI.EmitLate) {
+      NamedRegionTimer T(HI.TimerName, HI.TimerDescription, HI.TimerGroupName,
+                         HI.TimerGroupDescription, TimePassesIsEnabled);
+      HI.Handler->endModule();
+    }
+    delete HI.Handler;
+  }
+  Handlers.clear();
+  DD = nullptr;
+
+  // Emit late handlers (debug info).
+
   MMI = nullptr;
 
   OutStreamer->Finish();
   OutStreamer->reset();
 
   return false;
 }
 

test/DebugInfo/X86/arange-and-stub.ll

 ; RUN: llc -generate-arange-section -relocation-model=pic < %s | FileCheck %s
 
 ; CHECK:   .data
 ; CHECK-NOT: .section
 ; CHECK: .L_ZTId.DW.stub:
 
-; CHECK:  .data
+; CHECK:  .data{{$}}
 ; CHECK-NEXT: .Lsec_end0:
 
 source_filename = "test/DebugInfo/X86/arange-and-stub.ll"
 target triple = "x86_64-linux-gnu"
 
 @_ZTId = external constant i8*
 @zed = global [1 x void ()*] [void ()* @bar], !dbg !0