[DebugInfo][RemoveDIs] Instrument inliner for non-instr debug-info (#72884)

With intrinsics representing debug-info, we just clone all the
intrinsics when inlining a function and don't think about it any
further. With non-instruction debug-info however we need to be a bit
more careful and manually move the debug-info from one place to another.
For the most part, this means keeping a "cursor" during block cloning of
where we last copied debug-info from, and performing debug-info copying
whenever we successfully clone another instruction.

There are several utilities in LLVM for doing this, all of which now
need to manually call cloneDebugInfo. The testing story for this is not
well covered as we could rely on normal instruction-cloning mechanisms
to do all the hard stuff. Thus, I've added a few tests to explicitly
test dbg.value behaviours, ahead of them becoming not-instructions.

Author: jmorse

llvm/include/llvm/IR/DebugInfo.h

@@ -102,10 +102,12 @@ class DebugInfoFinder {
   /// Process a single instruction and collect debug info anchors.
   void processInstruction(const Module &M, const Instruction &I);
 
-  /// Process DbgVariableIntrinsic.
-  void processVariable(const Module &M, const DbgVariableIntrinsic &DVI);
+  /// Process a DILocalVariable.
+  void processVariable(const Module &M, const DILocalVariable *DVI);
   /// Process debug info location.
   void processLocation(const Module &M, const DILocation *Loc);
+  // Process a DPValue, much like a DbgVariableIntrinsic.
+  void processDPValue(const Module &M, const DPValue &DPV);
 
   /// Process subprogram.
   void processSubprogram(DISubprogram *SP);

llvm/lib/IR/DebugInfo.cpp

@@ -205,10 +205,13 @@ void DebugInfoFinder::processCompileUnit(DICompileUnit *CU) {
 void DebugInfoFinder::processInstruction(const Module &M,
                                          const Instruction &I) {
   if (auto *DVI = dyn_cast<DbgVariableIntrinsic>(&I))
-    processVariable(M, *DVI);
+    processVariable(M, DVI->getVariable());
 
   if (auto DbgLoc = I.getDebugLoc())
     processLocation(M, DbgLoc.get());
+
+  for (const DPValue &DPV : I.getDbgValueRange())
+    processDPValue(M, DPV);
 }
 
 void DebugInfoFinder::processLocation(const Module &M, const DILocation *Loc) {
@@ -218,6 +221,11 @@ void DebugInfoFinder::processLocation(const Module &M, const DILocation *Loc) {
   processLocation(M, Loc->getInlinedAt());
 }
 
+void DebugInfoFinder::processDPValue(const Module &M, const DPValue &DPV) {
+  processVariable(M, DPV.getVariable());
+  processLocation(M, DPV.getDebugLoc().get());
+}
+
 void DebugInfoFinder::processType(DIType *DT) {
   if (!addType(DT))
     return;
@@ -292,15 +300,7 @@ void DebugInfoFinder::processSubprogram(DISubprogram *SP) {
 }
 
 void DebugInfoFinder::processVariable(const Module &M,
-                                      const DbgVariableIntrinsic &DVI) {
-  auto *N = dyn_cast<MDNode>(DVI.getVariable());
-  if (!N)
-    return;
-
-  auto *DV = dyn_cast<DILocalVariable>(N);
-  if (!DV)
-    return;
-
+                                      const DILocalVariable *DV) {
   if (!NodesSeen.insert(DV).second)
     return;
   processScope(DV->getScope());

llvm/lib/Transforms/Scalar/CallSiteSplitting.cpp

@@ -402,6 +402,7 @@ static void splitCallSite(CallBase &CB,
       NewPN->insertBefore(&*TailBB->begin());
       CurrentI->replaceAllUsesWith(NewPN);
     }
+    CurrentI->dropDbgValues();
     CurrentI->eraseFromParent();
     // We are done once we handled the first original instruction in TailBB.
     if (CurrentI == OriginalBegin)

llvm/lib/Transforms/Scalar/JumpThreading.cpp

@@ -3118,8 +3118,8 @@ bool JumpThreadingPass::threadGuard(BasicBlock *BB, IntrinsicInst *Guard,
     if (!isa<PHINode>(&*BI))
       ToRemove.push_back(&*BI);
 
-  Instruction *InsertionPoint = &*BB->getFirstInsertionPt();
-  assert(InsertionPoint && "Empty block?");
+  BasicBlock::iterator InsertionPoint = BB->getFirstInsertionPt();
+  assert(InsertionPoint != BB->end() && "Empty block?");
   // Substitute with Phis & remove.
   for (auto *Inst : reverse(ToRemove)) {
     if (!Inst->use_empty()) {
@@ -3129,6 +3129,7 @@ bool JumpThreadingPass::threadGuard(BasicBlock *BB, IntrinsicInst *Guard,
       NewPN->insertBefore(InsertionPoint);
       Inst->replaceAllUsesWith(NewPN);
     }
+    Inst->dropDbgValues();
     Inst->eraseFromParent();
   }
   return true;

llvm/lib/Transforms/Utils/CloneFunction.cpp

@@ -94,6 +94,7 @@ void llvm::CloneFunctionInto(Function *NewFunc, const Function *OldFunc,
                              const char *NameSuffix, ClonedCodeInfo *CodeInfo,
                              ValueMapTypeRemapper *TypeMapper,
                              ValueMaterializer *Materializer) {
+  NewFunc->setIsNewDbgInfoFormat(OldFunc->IsNewDbgInfoFormat);
   assert(NameSuffix && "NameSuffix cannot be null!");
 
 #ifndef NDEBUG
@@ -271,9 +272,13 @@ void llvm::CloneFunctionInto(Function *NewFunc, const Function *OldFunc,
            BB = cast<BasicBlock>(VMap[&OldFunc->front()])->getIterator(),
            BE = NewFunc->end();
        BB != BE; ++BB)
-    // Loop over all instructions, fixing each one as we find it...
-    for (Instruction &II : *BB)
+    // Loop over all instructions, fixing each one as we find it, and any
+    // attached debug-info records.
+    for (Instruction &II : *BB) {
       RemapInstruction(&II, VMap, RemapFlag, TypeMapper, Materializer);
+      RemapDPValueRange(II.getModule(), II.getDbgValueRange(), VMap, RemapFlag,
+                        TypeMapper, Materializer);
+    }
 
   // Only update !llvm.dbg.cu for DifferentModule (not CloneModule). In the
   // same module, the compile unit will already be listed (or not). When
@@ -331,6 +336,7 @@ Function *llvm::CloneFunction(Function *F, ValueToValueMapTy &VMap,
   // Create the new function...
   Function *NewF = Function::Create(FTy, F->getLinkage(), F->getAddressSpace(),
                                     F->getName(), F->getParent());
+  NewF->setIsNewDbgInfoFormat(F->IsNewDbgInfoFormat);
 
   // Loop over the arguments, copying the names of the mapped arguments over...
   Function::arg_iterator DestI = NewF->arg_begin();
@@ -496,6 +502,22 @@ void PruningFunctionCloner::CloneBlock(
   bool hasCalls = false, hasDynamicAllocas = false, hasStaticAllocas = false;
   bool hasMemProfMetadata = false;
 
+  // Keep a cursor pointing at the last place we cloned debug-info records from.
+  BasicBlock::const_iterator DbgCursor = StartingInst;
+  auto CloneDbgRecordsToHere =
+      [NewBB, &DbgCursor](Instruction *NewInst, BasicBlock::const_iterator II) {
+        if (!NewBB->IsNewDbgInfoFormat)
+          return;
+
+        // Clone debug-info records onto this instruction. Iterate through any
+        // source-instructions we've cloned and then subsequently optimised
+        // away, so that their debug-info doesn't go missing.
+        for (; DbgCursor != II; ++DbgCursor)
+          NewInst->cloneDebugInfoFrom(&*DbgCursor, std::nullopt, false);
+        NewInst->cloneDebugInfoFrom(&*II);
+        DbgCursor = std::next(II);
+      };
+
   // Loop over all instructions, and copy them over, DCE'ing as we go.  This
   // loop doesn't include the terminator.
   for (BasicBlock::const_iterator II = StartingInst, IE = --BB->end(); II != IE;
@@ -545,6 +567,8 @@ void PruningFunctionCloner::CloneBlock(
       hasMemProfMetadata |= II->hasMetadata(LLVMContext::MD_memprof);
     }
 
+    CloneDbgRecordsToHere(NewInst, II);
+
     if (CodeInfo) {
       CodeInfo->OrigVMap[&*II] = NewInst;
       if (auto *CB = dyn_cast<CallBase>(&*II))
@@ -602,6 +626,9 @@ void PruningFunctionCloner::CloneBlock(
     if (OldTI->hasName())
       NewInst->setName(OldTI->getName() + NameSuffix);
     NewInst->insertInto(NewBB, NewBB->end());
+
+    CloneDbgRecordsToHere(NewInst, OldTI->getIterator());
+
     VMap[OldTI] = NewInst; // Add instruction map to value.
 
     if (CodeInfo) {
@@ -613,6 +640,13 @@ void PruningFunctionCloner::CloneBlock(
 
     // Recursively clone any reachable successor blocks.
     append_range(ToClone, successors(BB->getTerminator()));
+  } else {
+    // If we didn't create a new terminator, clone DPValues from the old
+    // terminator onto the new terminator.
+    Instruction *NewInst = NewBB->getTerminator();
+    assert(NewInst);
+
+    CloneDbgRecordsToHere(NewInst, OldTI->getIterator());
   }
 
   if (CodeInfo) {
@@ -850,12 +884,22 @@ void llvm::CloneAndPruneIntoFromInst(Function *NewFunc, const Function *OldFunc,
                        TypeMapper, Materializer);
   }
 
+  // Do the same for DPValues, touching all the instructions in the cloned
+  // range of blocks.
+  Function::iterator Begin = cast<BasicBlock>(VMap[StartingBB])->getIterator();
+  for (BasicBlock &BB : make_range(Begin, NewFunc->end())) {
+    for (Instruction &I : BB) {
+      RemapDPValueRange(I.getModule(), I.getDbgValueRange(), VMap,
+                        ModuleLevelChanges ? RF_None : RF_NoModuleLevelChanges,
+                        TypeMapper, Materializer);
+    }
+  }
+
   // Simplify conditional branches and switches with a constant operand. We try
   // to prune these out when cloning, but if the simplification required
   // looking through PHI nodes, those are only available after forming the full
   // basic block. That may leave some here, and we still want to prune the dead
   // code as early as possible.
-  Function::iterator Begin = cast<BasicBlock>(VMap[StartingBB])->getIterator();
   for (BasicBlock &BB : make_range(Begin, NewFunc->end()))
     ConstantFoldTerminator(&BB);
 
@@ -944,10 +988,15 @@ void llvm::CloneAndPruneFunctionInto(
 void llvm::remapInstructionsInBlocks(ArrayRef<BasicBlock *> Blocks,
                                      ValueToValueMapTy &VMap) {
   // Rewrite the code to refer to itself.
-  for (auto *BB : Blocks)
-    for (auto &Inst : *BB)
+  for (auto *BB : Blocks) {
+    Module *M = BB->getModule();
+    for (auto &Inst : *BB) {
+      RemapDPValueRange(Inst.getModule(), Inst.getDbgValueRange(), VMap,
+                        RF_NoModuleLevelChanges | RF_IgnoreMissingLocals);
       RemapInstruction(&Inst, VMap,
                        RF_NoModuleLevelChanges | RF_IgnoreMissingLocals);
+    }
+  }
 }
 
 /// Clones a loop \p OrigLoop.  Returns the loop and the blocks in \p
@@ -1071,6 +1120,7 @@ BasicBlock *llvm::DuplicateInstructionsInSplitBetween(
     Instruction *New = BI->clone();
     New->setName(BI->getName());
     New->insertBefore(NewTerm);
+    New->cloneDebugInfoFrom(&*BI);
     ValueMapping[&*BI] = New;
 
     // Remap operands to patch up intra-block references.

llvm/lib/Transforms/Utils/CloneModule.cpp

@@ -61,6 +61,7 @@ std::unique_ptr<Module> llvm::CloneModule(
   New->setDataLayout(M.getDataLayout());
   New->setTargetTriple(M.getTargetTriple());
   New->setModuleInlineAsm(M.getModuleInlineAsm());
+  New->IsNewDbgInfoFormat = M.IsNewDbgInfoFormat;
 
   // Loop over all of the global variables, making corresponding globals in the
   // new module.  Here we add them to the VMap and to the new Module.  We

llvm/lib/Transforms/Utils/InlineFunction.cpp

@@ -1666,48 +1666,71 @@ static void fixupLineNumbers(Function *Fn, Function::iterator FI,
   // the call site location instead.
   bool NoInlineLineTables = Fn->hasFnAttribute("no-inline-line-tables");
 
-  for (; FI != Fn->end(); ++FI) {
-    for (BasicBlock::iterator BI = FI->begin(), BE = FI->end();
-         BI != BE; ++BI) {
-      // Loop metadata needs to be updated so that the start and end locs
-      // reference inlined-at locations.
-      auto updateLoopInfoLoc = [&Ctx, &InlinedAtNode,
-                                &IANodes](Metadata *MD) -> Metadata * {
-        if (auto *Loc = dyn_cast_or_null<DILocation>(MD))
-          return inlineDebugLoc(Loc, InlinedAtNode, Ctx, IANodes).get();
-        return MD;
-      };
-      updateLoopMetadataDebugLocations(*BI, updateLoopInfoLoc);
-
-      if (!NoInlineLineTables)
-        if (DebugLoc DL = BI->getDebugLoc()) {
-          DebugLoc IDL =
-              inlineDebugLoc(DL, InlinedAtNode, BI->getContext(), IANodes);
-          BI->setDebugLoc(IDL);
-          continue;
-        }
+  // Helper-util for updating the metadata attached to an instruction.
+  auto UpdateInst = [&](Instruction &I) {
+    // Loop metadata needs to be updated so that the start and end locs
+    // reference inlined-at locations.
+    auto updateLoopInfoLoc = [&Ctx, &InlinedAtNode,
+                              &IANodes](Metadata *MD) -> Metadata * {
+      if (auto *Loc = dyn_cast_or_null<DILocation>(MD))
+        return inlineDebugLoc(Loc, InlinedAtNode, Ctx, IANodes).get();
+      return MD;
+    };
+    updateLoopMetadataDebugLocations(I, updateLoopInfoLoc);
+
+    if (!NoInlineLineTables)
+      if (DebugLoc DL = I.getDebugLoc()) {
+        DebugLoc IDL =
+            inlineDebugLoc(DL, InlinedAtNode, I.getContext(), IANodes);
+        I.setDebugLoc(IDL);
+        return;
+      }
 
-      if (CalleeHasDebugInfo && !NoInlineLineTables)
-        continue;
+    if (CalleeHasDebugInfo && !NoInlineLineTables)
+      return;
 
-      // If the inlined instruction has no line number, or if inline info
-      // is not being generated, make it look as if it originates from the call
-      // location. This is important for ((__always_inline, __nodebug__))
-      // functions which must use caller location for all instructions in their
-      // function body.
+    // If the inlined instruction has no line number, or if inline info
+    // is not being generated, make it look as if it originates from the call
+    // location. This is important for ((__always_inline, __nodebug__))
+    // functions which must use caller location for all instructions in their
+    // function body.
 
-      // Don't update static allocas, as they may get moved later.
-      if (auto *AI = dyn_cast<AllocaInst>(BI))
-        if (allocaWouldBeStaticInEntry(AI))
-          continue;
+    // Don't update static allocas, as they may get moved later.
+    if (auto *AI = dyn_cast<AllocaInst>(&I))
+      if (allocaWouldBeStaticInEntry(AI))
+        return;
 
-      // Do not force a debug loc for pseudo probes, since they do not need to
-      // be debuggable, and also they are expected to have a zero/null dwarf
-      // discriminator at this point which could be violated otherwise.
-      if (isa<PseudoProbeInst>(BI))
-        continue;
+    // Do not force a debug loc for pseudo probes, since they do not need to
+    // be debuggable, and also they are expected to have a zero/null dwarf
+    // discriminator at this point which could be violated otherwise.
+    if (isa<PseudoProbeInst>(I))
+      return;
+
+    I.setDebugLoc(TheCallDL);
+  };
 
-      BI->setDebugLoc(TheCallDL);
+  // Helper-util for updating debug-info records attached to instructions.
+  auto UpdateDPV = [&](DPValue *DPV) {
+    assert(DPV->getDebugLoc() && "Debug Value must have debug loc");
+    if (NoInlineLineTables) {
+      DPV->setDebugLoc(TheCallDL);
+      return;
+    }
+    DebugLoc DL = DPV->getDebugLoc();
+    DebugLoc IDL =
+        inlineDebugLoc(DL, InlinedAtNode,
+                       DPV->getMarker()->getParent()->getContext(), IANodes);
+    DPV->setDebugLoc(IDL);
+  };
+
+  // Iterate over all instructions, updating metadata and debug-info records.
+  for (; FI != Fn->end(); ++FI) {
+    for (BasicBlock::iterator BI = FI->begin(), BE = FI->end(); BI != BE;
+         ++BI) {
+      UpdateInst(*BI);
+      for (DPValue &DPV : BI->getDbgValueRange()) {
+        UpdateDPV(&DPV);
+      }
     }
 
     // Remove debug info intrinsics if we're not keeping inline info.
@@ -1717,11 +1740,12 @@ static void fixupLineNumbers(Function *Fn, Function::iterator FI,
         if (isa<DbgInfoIntrinsic>(BI)) {
           BI = BI->eraseFromParent();
           continue;
+        } else {
+          BI->dropDbgValues();
         }
         ++BI;
       }
     }
-
   }
 }
 
@@ -2402,6 +2426,7 @@ llvm::InlineResult llvm::InlineFunction(CallBase &CB, InlineFunctionInfo &IFI,
       // Transfer all of the allocas over in a block.  Using splice means
       // that the instructions aren't removed from the symbol table, then
       // reinserted.
+      I.setTailBit(true);
       Caller->getEntryBlock().splice(InsertPoint, &*FirstNewBlock,
                                      AI->getIterator(), I);
     }