MachineModuleInfo: Initialize DbgInfoAvailable depending on debug_cus existing

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.

Differential Revision: https://reviews.llvm.org/D53885

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@345740 91177308-0d34-0410-b5e6-96231b3b80d8

Author: MatzeB

lib/CodeGen/AsmPrinter/CodeViewDebug.cpp

@@ -117,6 +117,7 @@ CodeViewDebug::CodeViewDebug(AsmPrinter *AP)
   if (!MMI->getModule()->getNamedMetadata("llvm.dbg.cu") ||
       !AP->getObjFileLowering().getCOFFDebugSymbolsSection()) {
     Asm = nullptr;
+    MMI->setDebugInfoAvailability(false);
     return;
   }
   // Tell MMI that we have debug info.

lib/CodeGen/AsmPrinter/DwarfDebug.cpp

@@ -701,15 +701,18 @@ sortGlobalExprs(SmallVectorImpl<DwarfCompileUnit::GlobalExpr> &GVEs) {
 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;

lib/CodeGen/MachineModuleInfo.cpp

@@ -206,10 +206,11 @@ 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;
 }
 

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

@@ -0,0 +1,26 @@
+; 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)