Recommit r212203: Don't try to construct debug LexicalScopes hierarch…

…y for functions that do not have top level debug information.

Reverted by Eric Christopher (Thanks!) in r212203 after Bob Wilson
reported LTO issues. Duncan Exon Smith and Aditya Nandakumar helped
provide a reduced reproduction, though the failure wasn't too hard to
guess, and even easier with the example to confirm.

The assertion that the subprogram metadata associated with an
llvm::Function matches the scope data referenced by the DbgLocs on the
instructions in that function is not valid under LTO. In LTO, a C++
inline function might exist in multiple CUs and the subprogram metadata
nodes will refer to the same llvm::Function. In this case, depending on
the order of the CUs, the first intance of the subprogram metadata may
not be the one referenced by the instructions in that function and the
assertion will fail.

A test case (test/DebugInfo/cross-cu-linkonce-distinct.ll) is added, the
assertion removed and a comment added to explain this situation.

This was then reverted again in r213581 as it caused PR20367. The root
cause of this was the early exit in LiveDebugVariables meant that
spurious DBG_VALUE intrinsics that referenced dead variables were not
removed, causing an assertion/crash later on. The fix is to have
LiveDebugVariables strip all DBG_VALUE intrinsics in functions without
debug info as they're not needed anyway. Test case added to cover this
situation (that occurs when a debug-having function is inlined into a
nodebug function) in test/DebugInfo/X86/nodebug_with_debug_loc.ll

Original commit message:

If a function isn't actually in a CU's subprogram list in the debug info
metadata, ignore all the DebugLocs and don't try to build scopes, track
variables, etc.

While this is possibly a minor optimization, it's also a correctness fix
for an incoming patch that will add assertions to LexicalScopes and the
debug info verifier to ensure that all scope chains lead to debug info
for the current function.

Fix up a few test cases that had broken/incomplete debug info that could
violate this constraint.

Add a test case where this occurs by design (inlining a
debug-info-having function in an attribute nodebug function - we want
this to work because /if/ the nodebug function is then inlined into a
debug-info-having function, it should be fine (and will work fine - we
just stitch the scopes up as usual), but should the inlining not happen
we need to not assert fail either).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213952 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/AsmPrinter/DwarfDebug.cpp

@@ -731,6 +731,8 @@ void DwarfDebug::beginModule() {
 
   const Module *M = MMI->getModule();
 
+  FunctionDIs = makeSubprogramMap(*M);
+
   // If module has named metadata anchors then use them, otherwise scan the
   // module using debug info finder to collect debug info.
   NamedMDNode *CU_Nodes = M->getNamedMetadata("llvm.dbg.cu");
@@ -1416,6 +1418,10 @@ void DwarfDebug::beginFunction(const MachineFunction *MF) {
   if (!MMI->hasDebugInfo())
     return;
 
+  auto DI = FunctionDIs.find(MF->getFunction());
+  if (DI == FunctionDIs.end())
+    return;
+
   // Grab the lexical scopes for the function, if we don't have any of those
   // then we're not going to be able to do anything.
   LScopes.initialize(*MF);
@@ -1431,6 +1437,14 @@ void DwarfDebug::beginFunction(const MachineFunction *MF) {
   // belongs to so that we add to the correct per-cu line table in the
   // non-asm case.
   LexicalScope *FnScope = LScopes.getCurrentFunctionScope();
+  // FnScope->getScopeNode() and DI->second should represent the same function,
+  // though they may not be the same MDNode due to inline functions merged in
+  // LTO where the debug info metadata still differs (either due to distinct
+  // written differences - two versions of a linkonce_odr function
+  // written/copied into two separate files, or some sub-optimal metadata that
+  // isn't structurally identical (see: file path/name info from clang, which
+  // includes the directory of the cpp file being built, even when the file name
+  // is absolute (such as an <> lookup header)))
   DwarfCompileUnit *TheCU = SPMap.lookup(FnScope->getScopeNode());
   assert(TheCU && "Unable to find compile unit!");
   if (Asm->OutStreamer.hasRawTextSupport())
@@ -1528,7 +1542,8 @@ void DwarfDebug::endFunction(const MachineFunction *MF) {
     assert(CurFn == MF);
   assert(CurFn != nullptr);
 
-  if (!MMI->hasDebugInfo() || LScopes.empty()) {
+  if (!MMI->hasDebugInfo() || LScopes.empty() ||
+      !FunctionDIs.count(MF->getFunction())) {
     // If we don't have a lexical scope for this function then there will
     // be a hole in the range information. Keep note of this by setting the
     // previously used section to nullptr.

lib/CodeGen/AsmPrinter/DwarfDebug.h

@@ -330,6 +330,8 @@ class DwarfDebug : public AsmPrinterHandler {
   DwarfAccelTable AccelNamespace;
   DwarfAccelTable AccelTypes;
 
+  DenseMap<const Function *, DISubprogram> FunctionDIs;
+
   MCDwarfDwoLineTable *getDwoLineTable(const DwarfCompileUnit &);
 
   void addScopeVariable(LexicalScope *LS, DbgVariable *Var);

lib/CodeGen/LiveDebugVariables.cpp

@@ -329,12 +329,13 @@ class LDVImpl {
   void computeIntervals();
 
 public:
-  LDVImpl(LiveDebugVariables *ps) : pass(*ps), EmitDone(false),
-                                    ModifiedMF(false) {}
+  LDVImpl(LiveDebugVariables *ps)
+      : pass(*ps), MF(nullptr), EmitDone(false), ModifiedMF(false) {}
   bool runOnMachineFunction(MachineFunction &mf);
 
   /// clear - Release all memory.
   void clear() {
+    MF = nullptr;
     userValues.clear();
     virtRegToEqClass.clear();
     userVarMap.clear();
@@ -693,11 +694,11 @@ void LDVImpl::computeIntervals() {
 }
 
 bool LDVImpl::runOnMachineFunction(MachineFunction &mf) {
+  clear();
   MF = &mf;
   LIS = &pass.getAnalysis<LiveIntervals>();
   MDT = &pass.getAnalysis<MachineDominatorTree>();
   TRI = mf.getTarget().getRegisterInfo();
-  clear();
   LS.initialize(mf);
   DEBUG(dbgs() << "********** COMPUTING LIVE DEBUG VARIABLES: "
                << mf.getName() << " **********\n");
@@ -709,9 +710,25 @@ bool LDVImpl::runOnMachineFunction(MachineFunction &mf) {
   return Changed;
 }
 
+static void removeDebugValues(MachineFunction &mf) {
+  for (MachineBasicBlock &MBB : mf) {
+    for (auto MBBI = MBB.begin(), MBBE = MBB.end(); MBBI != MBBE; ) {
+      if (!MBBI->isDebugValue()) {
+        ++MBBI;
+        continue;
+      }
+      MBBI = MBB.erase(MBBI);
+    }
+  }
+}
+
 bool LiveDebugVariables::runOnMachineFunction(MachineFunction &mf) {
   if (!EnableLDV)
     return false;
+  if (!FunctionDIs.count(mf.getFunction())) {
+    removeDebugValues(mf);
+    return false;
+  }
   if (!pImpl)
     pImpl = new LDVImpl(this);
   return static_cast<LDVImpl*>(pImpl)->runOnMachineFunction(mf);
@@ -974,6 +991,8 @@ void UserValue::emitDebugValues(VirtRegMap *VRM, LiveIntervals &LIS,
 
 void LDVImpl::emitDebugValues(VirtRegMap *VRM) {
   DEBUG(dbgs() << "********** EMITTING LIVE DEBUG VARIABLES **********\n");
+  if (!MF)
+    return;
   const TargetInstrInfo *TII = MF->getTarget().getInstrInfo();
   for (unsigned i = 0, e = userValues.size(); i != e; ++i) {
     DEBUG(userValues[i]->print(dbgs(), &MF->getTarget()));
@@ -988,6 +1007,10 @@ void LiveDebugVariables::emitDebugValues(VirtRegMap *VRM) {
     static_cast<LDVImpl*>(pImpl)->emitDebugValues(VRM);
 }
 
+bool LiveDebugVariables::doInitialization(Module &M) {
+  FunctionDIs = makeSubprogramMap(M);
+  return Pass::doInitialization(M);
+}
 
 #ifndef NDEBUG
 void LiveDebugVariables::dump() {

lib/CodeGen/LiveDebugVariables.h

@@ -22,6 +22,7 @@
 #define LLVM_CODEGEN_LIVEDEBUGVARIABLES_H
 
 #include "llvm/ADT/ArrayRef.h"
+#include "llvm/IR/DebugInfo.h"
 #include "llvm/CodeGen/MachineFunctionPass.h"
 
 namespace llvm {
@@ -32,6 +33,7 @@ class VirtRegMap;
 
 class LiveDebugVariables : public MachineFunctionPass {
   void *pImpl;
+  DenseMap<const Function*, DISubprogram> FunctionDIs;
 public:
   static char ID; // Pass identification, replacement for typeid
 
@@ -64,6 +66,7 @@ class LiveDebugVariables : public MachineFunctionPass {
   bool runOnMachineFunction(MachineFunction &) override;
   void releaseMemory() override;
   void getAnalysisUsage(AnalysisUsage &) const override;
+  bool doInitialization(Module &) override;
 
 };
 

test/CodeGen/X86/2010-06-01-DeadArg-DbgInfo.ll

@@ -24,7 +24,7 @@ declare void @llvm.dbg.value(metadata, i64, metadata) nounwind readnone
 !llvm.dbg.lv = !{!0, !14, !15, !16, !17, !24, !25, !28}
 
 !0 = metadata !{i32 786689, metadata !1, metadata !"this", metadata !3, i32 11, metadata !12, i32 0, null} ; [ DW_TAG_arg_variable ]
-!1 = metadata !{i32 786478, metadata !31, metadata !2, metadata !"bar", metadata !"bar", metadata !"_ZN3foo3barEi", i32 11, metadata !9, i1 false, i1 true, i32 0, i32 0, null, i32 0, i1 true, i32 (%struct.foo*, i32)* @_ZN3foo3bazEi, null, null, null, i32 11} ; [ DW_TAG_subprogram ]
+!1 = metadata !{i32 786478, metadata !31, metadata !2, metadata !"bar", metadata !"bar", metadata !"_ZN3foo3barEi", i32 11, metadata !9, i1 false, i1 true, i32 0, i32 0, null, i32 0, i1 true, i32 (%struct.foo*, i32)* null, null, null, null, i32 11} ; [ DW_TAG_subprogram ]
 !2 = metadata !{i32 786451, metadata !31, metadata !3, metadata !"foo", i32 3, i64 32, i64 32, i64 0, i32 0, null, metadata !5, i32 0, null, null, null} ; [ DW_TAG_structure_type ] [foo] [line 3, size 32, align 32, offset 0] [def] [from ]
 !3 = metadata !{i32 786473, metadata !31} ; [ DW_TAG_file_type ]
 !4 = metadata !{i32 786449, metadata !31, i32 4, metadata !"4.2.1 LLVM build", i1 true, metadata !"", i32 0, metadata !32, metadata !32, metadata !33, null, null, metadata !""} ; [ DW_TAG_compile_unit ]