MachineModuleInfo: Initialize DbgInfoAvailable depending on debug_cus existing

[MatzeB]

Summary

Before this patch DbgInfoAvailable was set to true in
DwarfDebug::beginModule() or CodeViewDebug::CodeViewDebug(). This made
MIR testing weird, since passes would suddenly stop dealing with debug
info just because we stopped the pipeline before the debug printers.

This patch changes the logic to initialize DbgInfoAvailable based on the
fact that debug_compile_units exist in the llvm Module. The debug
printers may then override it with false in case of debug printing being
disabled.

[dblaikie]

Sounds like this could have a test case, if it's meant to facilitate easier testing?

lib/CodeGen/MachineModuleInfo.cpp

214 ↗

(On Diff #171770)

maybe:

empty(M.debug_compile_units());

(we should have/add an llvm::empty(Range) template somewhere in STLExtras or the like, I think - that compares begin/end - maybe it should be called is_empty, I guess, to clarify that it isn't mutating a container... )

[MatzeB]

• Use empty implementation from https://reviews.llvm.org/D53909
• Add a test (I wish writing minimal debug info tests was simpler than this...)

[dblaikie]

test/CodeGen/AArch64/fast-isel-dbg.ll

6–18 ↗

(On Diff #171851)

Probably put this metadata after the rest of the code, as it's usually printed (this also has the effect of moving the CHECKs (and the original dbg.declare in question) up closer to the RUN lines, so it's a bit easier to see how all the testing is related

llvm/trunk/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp

 
 CodeViewDebug::CodeViewDebug(AsmPrinter *AP)
     : DebugHandlerBase(AP), OS(*Asm->OutStreamer), TypeTable(Allocator) {
   // If module doesn't have named metadata anchors or COFF debug section
   // is not available, skip any debug info related stuff.
   if (!MMI->getModule()->getNamedMetadata("llvm.dbg.cu") ||
       !AP->getObjFileLowering().getCOFFDebugSymbolsSection()) {
     Asm = nullptr;
+    MMI->setDebugInfoAvailability(false);
     return;
   }
   // Tell MMI that we have debug info.
   MMI->setDebugInfoAvailability(true);
 
   TheCPU =
       mapArchToCVCPUType(Triple(MMI->getModule()->getTargetTriple()).getArch());
 }

llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

 }
 
 // Emit all Dwarf sections that should come prior to the content. Create
 // global DIEs and emit initial debug info sections. This is invoked by
 // the target AsmPrinter.
 void DwarfDebug::beginModule() {
   NamedRegionTimer T(DbgTimerName, DbgTimerDescription, DWARFGroupName,
                      DWARFGroupDescription, TimePassesIsEnabled);
-  if (DisableDebugInfoPrinting)
+  if (DisableDebugInfoPrinting) {
+    MMI->setDebugInfoAvailability(false);
     return;
+  }
 
   const Module *M = MMI->getModule();
 
   unsigned NumDebugCUs = std::distance(M->debug_compile_units_begin(),
                                        M->debug_compile_units_end());
   // Tell MMI whether we have debug info.
-  MMI->setDebugInfoAvailability(NumDebugCUs > 0);
+  assert(MMI->hasDebugInfo() == (NumDebugCUs > 0) &&
+         "DebugInfoAvailabilty initialized unexpectedly");
   SingleCU = NumDebugCUs == 1;
   DenseMap<DIGlobalVariable *, SmallVector<DwarfCompileUnit::GlobalExpr, 1>>
       GVMap;
   for (const GlobalVariable &Global : M->globals()) {
     SmallVector<DIGlobalVariableExpression *, 1> GVs;
     Global.getDebugInfo(GVs);
     for (auto *GVE : GVs)
       GVMap[GVE->getVariable()].push_back({&Global, GVE->getExpression()});

llvm/trunk/lib/CodeGen/MachineModuleInfo.cpp

MachineModuleInfo::MachineModuleInfo(const TargetMachine *TM)
   initializeMachineModuleInfoPass(*PassRegistry::getPassRegistry());
 }
 
 MachineModuleInfo::~MachineModuleInfo() = default;
 
 bool MachineModuleInfo::doInitialization(Module &M) {
   ObjFileMMI = nullptr;
   CurCallSite = 0;
-  DbgInfoAvailable = UsesVAFloatArgument = UsesMorestackAddr = false;
+  UsesVAFloatArgument = UsesMorestackAddr = false;
   HasSplitStack = HasNosplitStack = false;
   AddrLabelSymbols = nullptr;
   TheModule = &M;
+  DbgInfoAvailable = !empty(M.debug_compile_units());
   return false;
 }
 
 bool MachineModuleInfo::doFinalization(Module &M) {
   Personalities.clear();
 
   delete AddrLabelSymbols;
   AddrLabelSymbols = nullptr;

llvm/trunk/test/CodeGen/AArch64/fast-isel-dbg.ll

+; RUN: llc -o - %s -fast-isel -stop-before=expand-isel-pseudos | FileCheck %s
+; Make sure fast-isel produces DBG_VALUE instructions even if no debug printer
+; is scheduled because of -stop-before.
+target triple="aarch64--"
+
+; CHECK-LABEL: name: func
+; CHECK: DBG_VALUE
+define void @func(i32 %a) !dbg !4 {
+  call void @llvm.dbg.declare(metadata i32 %a, metadata !5, metadata !DIExpression()), !dbg !7
+  ret void
+}
+
+declare void @llvm.dbg.declare(metadata, metadata, metadata) #0
+attributes #0 = { nounwind readnone speculatable }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2, !3}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C, file: !1, isOptimized: false, runtimeVersion: 0, emissionKind: LineTablesOnly)
+!1 = !DIFile(filename: "fast-isel-dbg.ll", directory: "/")
+!2 = !{i32 2, !"Dwarf Version", i32 4}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = distinct !DISubprogram(name: "func", scope: null, isLocal: false, isDefinition: true, isOptimized: false, unit: !0)
+!5 = !DILocalVariable(name: "a", arg: 1, scope: !4, file: !1, line: 17, type: !6)
+!6 = !DIBasicType(name: "unsigned int", size: 32, encoding: DW_ATE_unsigned)
+!7 = !DILocation(line: 17, scope: !4)