[Assignment Tracking][12/*] Account for assignment tracking in mem2reg

[Orlando]

Summary

The changes for assignment tracking don't require much of a deviation from existing behaviour. dbg.assign intrinsics linked to an alloca are treated much in the same way as dbg.declare users of an alloca, except that we don't insert dbg.value intrinsics to describe assignments when there is already a dbg.assign intrinsic present, e.g. one linked to a store that is going to be removed.

[jmorse]

Possibly I've missed something -- there's nothing here that's converting dbg.declares to dbg.assigns, so it's up to the frontend to produce appropriate dbg.assigns initially, yes?

llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp

105

This will want a top-level docu-comment if there are members that are docucommented.

324

Docu-comment etc

692

The original authors saw fit to guard the copying of Info.DbgUsers by empty(), best to continue the pattern by guarding the copying of Info.AssignmentTracking.

[Orlando]

In D133295#3774554, @jmorse wrote:

Possibly I've missed something -- there's nothing here that's converting dbg.declares to dbg.assigns, so it's up to the frontend to produce appropriate dbg.assigns initially, yes?

Yep, in D132226 Clang injects the pass AssignmentTrackingPass, which added in D132225, into the optimization pipeline. It runs before any optimizations.

N.B. (possibly going off on a tangent here): originally, in the prototype, the initial dbg.assign-inserting was done from the front end, but the implementation basically had the same behaviour as that pass (convert dbg.declares to dbg.assigns). Using a pass has advantages in that it can be tested, and it's less invasive in Clang, and provides a cheap/easy way for front ends to try out assignment tracking. In the long run we should probably aim to deprecate the pass (and dbg.declare) and get front ends to produce the intrinsics themselves, but I think this is a good staging step.

[jmorse]

A small risk here is that there are promotion-parts of mem2reg that aren't covered; I think if there are, they'll show up when tests are converted to use dbg.assigns rather than dbg.value.

In the tests where allocas are deleted, should we not be testing that the alloca reference in the dbg.assigns are replaced with undef?

Probably beyond the call of duty, but there's no need for the tbaa metadata to be part of these tests, and it'll reduce unrelated maintenance if we can drop it.

(Otherwise looks good)

llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp

106

It isn't a comprehensive set though, right? From the constructor, it's a sample of one dbg.assign per DebugVariable. The purpose being that they act like a dbg.declare, the reference for creating dbg.values?

133–140

Am I right in thinking that this is where un-linked stores have an effect on variables, i.e., if we promote something off the stack and there are some unlinked stores, then they get dbg.values created for them here?

If so, IMO better to word the comment from that perspective. I think it's a style thing, but I'd flip the focus of the sentence to the open with "Stores that are not linked to dbg.assigns...", that gives the reader more context about what the purpose of this code is.

158–159

Need to use at::getAssignmentMarkers(AI) again because DbgAssigns filters some of the dbg.assigns out?

[Orlando]

+ Addressed review comments.

A small risk here is that there are promotion-parts of mem2reg that aren't covered; I think if there are, they'll show up when tests are converted to use dbg.assigns rather than dbg.value.

To the best of my knowledge I got them all, but it's definitely a risk.

In the tests where allocas are deleted, should we not be testing that the alloca reference in the dbg.assigns are replaced with undef?

Done.

Probably beyond the call of duty, but there's no need for the tbaa metadata to be part of these tests, and it'll reduce unrelated maintenance if we can drop it.

Done.

llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp

133–140

I think you understand this correctly and I have updated the comment to hopefully better explain. How does this look?

158–159

That is true, nice catch. I've added a new function deleteAssignmentMarkers(const Instruction *) in a new patch D133576, which is now called directly in place of calls to updateForDeletedAlloca, which I've now removed.

I've modified the test single-store-alloca.ll to check this works as expected.

692

Done. I think this should be okay - if the resize performed on AllocaATInfo before this loop behaves like a std::vector::resize IIUC it should result in the AssignmentTrackingInfo element member DbgAssigns being default-initialized. So everything should be okay if the assignment is skipped.

[jmorse]

LGTM with a microscopic wording nit that you don't need to worry abuot.

llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp

133–140

Sounds good; you might want to shoe-horn in the fact that untracked stores should be rare, and are typically undesirable, it should set the right tone in the mind of the reader.

(A lot of these comments are about making the future reader think the right thoughts, for when someone comes and redesigns this in n years time, in which case they should ask themselves "why were untracked stores considered undesirable", and come back to the what-is-the-source-of-truth problems that have been discussed).

llvm/lib/Transforms/Utils/Local.cpp

static bool valueCoversEntireFragment(Type *ValTy, DbgVariableIntrinsic *DII) {
   // Could not determine size of variable. Conservatively return false.
   return false;
 }
 
 /// Inserts a llvm.dbg.value intrinsic before a store to an alloca'd value
 /// that has an associated llvm.dbg.declare or llvm.dbg.addr intrinsic.
 void llvm::ConvertDebugDeclareToDebugValue(DbgVariableIntrinsic *DII,
                                            StoreInst *SI, DIBuilder &Builder) {
-  assert(DII->isAddressOfVariable());
+  assert(DII->isAddressOfVariable() || isa<DbgAssignIntrinsic>(DII));
   auto *DIVar = DII->getVariable();
   assert(DIVar && "Missing variable");
   auto *DIExpr = DII->getExpression();
   Value *DV = SI->getValueOperand();
 
   DebugLoc NewLoc = getDebugValueLoc(DII);
 
   if (!valueCoversEntireFragment(DV->getType(), DII)) {

llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp

for (const User *U : AI->users()) {
     }
   }
 
   return true;
 }
 
 namespace {
 
+class AssignmentTrackingInfo {
+  /// DbgAssignIntrinsics linked to the alloca.
+  SmallVector<DbgVariableIntrinsic *> DbgAssigns;
+
+public:
+  void init(AllocaInst *AI) {
+    SmallSet<DebugVariable, 2> Vars;
+    for (DbgAssignIntrinsic *DAI : at::getAssignmentMarkers(AI)) {
+      if (Vars.insert(DebugVariable(DAI)).second)
+        DbgAssigns.push_back(DAI);
+    }
+  }
+
+  /// Update assignment tracking debug info given for the to-be-deleted store
+  /// \p ToDelete that stores to this alloca.
+  void updateForDeletedStore(StoreInst *ToDelete, DIBuilder &DIB) const {
+    // There's nothing to do if the alloca doesn't have any variables using
+    // assignment tracking.
+    if (DbgAssigns.empty()) {
+      assert(at::getAssignmentMarkers(ToDelete).empty());
+      return;
+    }
+
+    // Just leave dbg.assign intrinsics in place.
+    SmallSet<DebugVariable, 2> Ignore;
+    for (DbgAssignIntrinsic *DAI : at::getAssignmentMarkers(ToDelete))
+      Ignore.insert(DebugVariable(DAI));
+
+    // Insert dbg.value intrinsics for variables that are using
+    // assignment tracking but don't have a dbg.assign linked to
+    // this store.
+    for (auto *DAI : DbgAssigns) {
+      if (Ignore.contains(DebugVariable(DAI)))
+        continue;
+      ConvertDebugDeclareToDebugValue(DAI, ToDelete, DIB);
+    }
+  }
+
+  /// Update assignment tracking debug info given for the newly inserted PHI \p
+  /// NewPhi.
+  void updateForNewPhi(PHINode *NewPhi, DIBuilder &DIB) const {
+    // Regardless of the position of dbg.assigns relative to stores, the
+    // incoming values into a new PHI should be the same for the (imaginary)
+    // debug-phi.
+    for (auto *DAI : DbgAssigns)
+      ConvertDebugDeclareToDebugValue(DAI, NewPhi, DIB);
+  }
+
+  /// Update assignment tracking debug info for this alloca that is about to be
+  /// deleted.
+  void updateForDeletedAlloca() const {
+    // Remove the dbg.assign intrinsics that are linked to the alloca since they
+    // don't provide any useful information once it is deleted.
+    for (auto *DAI : DbgAssigns)
+      DAI->eraseFromParent();
+  }
+
+  void clear() { DbgAssigns.clear(); }
+};
+
 struct AllocaInfo {
   using DbgUserVec = SmallVector<DbgVariableIntrinsic *, 1>;
 
   SmallVector<BasicBlock *, 32> DefiningBlocks;
   SmallVector<BasicBlock *, 32> UsingBlocks;
 
   StoreInst *OnlyStore;
   BasicBlock *OnlyBlock;
   bool OnlyUsedInOneBlock;
 
+  /// Debug users of the alloca - does not include dbg.assign intrinsics.
   DbgUserVec DbgUsers;
+  /// Helper to update assignment tracking debug info.
+  AssignmentTrackingInfo AssignmentTracking;
 
   void clear() {
     DefiningBlocks.clear();
     UsingBlocks.clear();
     OnlyStore = nullptr;
     OnlyBlock = nullptr;
     OnlyUsedInOneBlock = true;
     DbgUsers.clear();
+    AssignmentTracking.clear();
   }
 
   /// Scan the uses of the specified alloca, filling in the AllocaInfo used
   /// by the rest of the pass to reason about the uses of this alloca.
   void AnalyzeAlloca(AllocaInst *AI) {
     clear();
 
     // As we scan the uses of the alloca instruction, keep track of stores,
for (User *U : AI->users()) {
 
       if (OnlyUsedInOneBlock) {
         if (!OnlyBlock)
           OnlyBlock = User->getParent();
         else if (OnlyBlock != User->getParent())
           OnlyUsedInOneBlock = false;
       }
     }
-
-    findDbgUsers(DbgUsers, AI);
+    DbgUserVec AllDbgUsers;
+    findDbgUsers(AllDbgUsers, AI);
+    std::copy_if(AllDbgUsers.begin(), AllDbgUsers.end(),
+                 std::back_inserter(DbgUsers), [](DbgVariableIntrinsic *DII) {
+                   return !isa<DbgAssignIntrinsic>(DII);
+                 });
+    AssignmentTracking.init(AI);
   }
 };
 
 /// Data package used by RenamePass().
 struct RenamePassData {
   using ValVector = std::vector<Value *>;
   using LocationVector = std::vector<DebugLoc>;
 
struct PromoteMem2Reg {
   /// For each PHI node, keep track of which entry in Allocas it corresponds
   /// to.
   DenseMap<PHINode *, unsigned> PhiToAllocaMap;
 
   /// For each alloca, we keep track of the dbg.declare intrinsic that
   /// describes it, if any, so that we can convert it to a dbg.value
   /// intrinsic if the alloca gets promoted.
   SmallVector<AllocaInfo::DbgUserVec, 8> AllocaDbgUsers;
+  SmallVector<AssignmentTrackingInfo, 8> AllocaATInfo;
 
   /// The set of basic blocks the renamer has already visited.
   SmallPtrSet<BasicBlock *, 16> Visited;
 
   /// Contains a stable numbering of basic blocks to avoid non-determinstic
   /// behavior.
   DenseMap<BasicBlock *, unsigned> BBNumbers;
 
for (User *U : make_early_inc_range(AI->users())) {
     LI->eraseFromParent();
     LBI.deleteValue(LI);
   }
 
   // Finally, after the scan, check to see if the store is all that is left.
   if (!Info.UsingBlocks.empty())
     return false; // If not, we'll have to fall back for the remainder.
 
+  DIBuilder DIB(*AI->getModule(), /*AllowUnresolved*/ false);
+  // Update assignment tracking info for the store we're going to delete.
+  Info.AssignmentTracking.updateForDeletedStore(Info.OnlyStore, DIB);
+
   // Record debuginfo for the store and remove the declaration's
   // debuginfo.
   for (DbgVariableIntrinsic *DII : Info.DbgUsers) {
     if (DII->isAddressOfVariable()) {
-      DIBuilder DIB(*AI->getModule(), /*AllowUnresolved*/ false);
       ConvertDebugDeclareToDebugValue(DII, Info.OnlyStore, DIB);
       DII->eraseFromParent();
     } else if (DII->getExpression()->startsWithDeref()) {
       DII->eraseFromParent();
     }
   }
+
+  // Update assignment tracking info now that we're deleting the alloca.
+  Info.AssignmentTracking.updateForDeletedAlloca();
+
   // Remove the (now dead) store and alloca.
   Info.OnlyStore->eraseFromParent();
   LBI.deleteValue(Info.OnlyStore);
 
   AI->eraseFromParent();
   return true;
 }
 
if (I == StoresByIndex.begin()) {
       LI->replaceAllUsesWith(ReplVal);
     }
 
     LI->eraseFromParent();
     LBI.deleteValue(LI);
   }
 
   // Remove the (now dead) stores and alloca.
+  DIBuilder DIB(*AI->getModule(), /*AllowUnresolved*/ false);
   while (!AI->use_empty()) {
     StoreInst *SI = cast<StoreInst>(AI->user_back());
+    // Update assignment tracking info for the store we're going to delete.
+    Info.AssignmentTracking.updateForDeletedStore(SI, DIB);
     // Record debuginfo for the store before removing it.
     for (DbgVariableIntrinsic *DII : Info.DbgUsers) {
       if (DII->isAddressOfVariable()) {
-        DIBuilder DIB(*AI->getModule(), /*AllowUnresolved*/ false);
         ConvertDebugDeclareToDebugValue(DII, SI, DIB);
       }
     }
     SI->eraseFromParent();
     LBI.deleteValue(SI);
   }
 
+  // Update assignment tracking info now that we're deleting the alloca.
+  Info.AssignmentTracking.updateForDeletedAlloca();
   AI->eraseFromParent();
 
   // The alloca's debuginfo can be removed as well.
   for (DbgVariableIntrinsic *DII : Info.DbgUsers)
     if (DII->isAddressOfVariable() || DII->getExpression()->startsWithDeref())
       DII->eraseFromParent();
 
   ++NumLocalPromoted;
   return true;
 }
 
 void PromoteMem2Reg::run() {
   Function &F = *DT.getRoot()->getParent();
 
   AllocaDbgUsers.resize(Allocas.size());
+  AllocaATInfo.resize(Allocas.size());
 
   AllocaInfo Info;
   LargeBlockInfo LBI;
   ForwardIDFCalculator IDF(DT);
 
   for (unsigned AllocaNum = 0; AllocaNum != Allocas.size(); ++AllocaNum) {
     AllocaInst *AI = Allocas[AllocaNum];
 
if (BBNumbers.empty()) {
       unsigned ID = 0;
       for (auto &BB : F)
         BBNumbers[&BB] = ID++;
     }
 
     // Remember the dbg.declare intrinsic describing this alloca, if any.
     if (!Info.DbgUsers.empty())
       AllocaDbgUsers[AllocaNum] = Info.DbgUsers;
+    AllocaATInfo[AllocaNum] = Info.AssignmentTracking;
 
     // Keep the reverse mapping of the 'Allocas' array for the rename pass.
     AllocaLookup[Allocas[AllocaNum]] = AllocaNum;
 
     // Unique the set of defining blocks for efficient lookup.
     SmallPtrSet<BasicBlock *, 32> DefBlocks(Info.DefiningBlocks.begin(),
                                             Info.DefiningBlocks.end());
 
for (Instruction *A : Allocas) {
     // unreachable basic blocks that were not processed by walking the dominator
     // tree. Just delete the users now.
     if (!A->use_empty())
       A->replaceAllUsesWith(PoisonValue::get(A->getType()));
     A->eraseFromParent();
   }
 
   // Remove alloca's dbg.declare instrinsics from the function.
+  for (auto &ATInfo : AllocaATInfo)
+    ATInfo.updateForDeletedAlloca();
   for (auto &DbgUsers : AllocaDbgUsers) {
     for (auto *DII : DbgUsers)
       if (DII->isAddressOfVariable() || DII->getExpression()->startsWithDeref())
         DII->eraseFromParent();
   }
 
   // Loop over all of the PHI nodes and see if there are any that we can get
   // rid of because they merge all of the same incoming values.  This can
if (PhiToAllocaMap.count(APN)) {
                                        APN->getNumIncomingValues() > 0);
 
         // Add N incoming values to the PHI node.
         for (unsigned i = 0; i != NumEdges; ++i)
           APN->addIncoming(IncomingVals[AllocaNo], Pred);
 
         // The currently active variable for this block is now the PHI.
         IncomingVals[AllocaNo] = APN;
+        AllocaATInfo[AllocaNo].updateForNewPhi(APN, DIB);
         for (DbgVariableIntrinsic *DII : AllocaDbgUsers[AllocaNo])
           if (DII->isAddressOfVariable())
             ConvertDebugDeclareToDebugValue(DII, APN, DIB);
 
         // Get the next phi node.
         ++PNI;
         APN = dyn_cast<PHINode>(PNI);
         if (!APN)
if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
         continue;
 
       // what value were we writing?
       unsigned AllocaNo = ai->second;
       IncomingVals[AllocaNo] = SI->getOperand(0);
 
       // Record debuginfo for the store before removing it.
       IncomingLocs[AllocaNo] = SI->getDebugLoc();
+      AllocaATInfo[AllocaNo].updateForDeletedStore(SI, DIB);
       for (DbgVariableIntrinsic *DII : AllocaDbgUsers[ai->second])
         if (DII->isAddressOfVariable())
           ConvertDebugDeclareToDebugValue(DII, SI, DIB);
       BB->getInstList().erase(SI);
     }
   }
 
   // 'Recurse' to our successors.

llvm/test/DebugInfo/Generic/assignment-tracking/mem2reg/phi.ll

+; RUN: opt -passes=mem2reg -S %s -o - -experimental-assignment-tracking \
+; RUN: | FileCheck %s --implicit-check-not="call void @llvm.dbg"
+
+;; Test assignment tracking debug info when mem2reg promotes an alloca with
+;; stores requiring insertion of a phi. Check the output when the stores are
+;; tagged and also untagged (test manually updated for the latter by linking a
+;; dbg.assgin for another variable "b" to the alloca).
+
+; CHECK: entry:
+; CHECK-NEXT: call void @llvm.dbg.value(metadata i32 %a, metadata ![[B:[0-9]+]]
+; CHECK-NEXT: call void @llvm.dbg.assign(metadata i32 %a, metadata ![[A:[0-9]+]]
+; CHECK: if.then:
+; CHECK-NEXT: %add =
+; CHECK-NEXT: call void @llvm.dbg.value(metadata i32 %add, metadata ![[B]]
+; CHECK-NEXT: call void @llvm.dbg.assign(metadata i32 %add, metadata ![[A]]
+; CHECK: if.else:
+; CHECK-NEXT: call void @llvm.dbg.value(metadata i32 -1, metadata ![[B]]
+; CHECK-NEXT: call void @llvm.dbg.assign(metadata i32 -1, metadata ![[A]]
+; CHECK: if.end:
+; CHECK-NEXT: %a.addr.0 = phi i32
+; CHECK-NEXT: call void @llvm.dbg.value(metadata i32 %a.addr.0, metadata ![[A]]
+; CHECK-NEXT: call void @llvm.dbg.value(metadata i32 %a.addr.0, metadata ![[B]]
+
+; CHECK-DAG: ![[A]] = !DILocalVariable(name: "a",
+; CHECK-DAG: ![[B]] = !DILocalVariable(name: "b",
+
+;; $ cat test.cpp
+;; int f(int a) {
+;;   if (a)
+;;     a += 1;
+;;   else
+;;     a = -1;
+;;   return a;
+;; }
+
+define dso_local noundef i32 @_Z1fi(i32 noundef %a) #0 !dbg !7 {
+entry:
+  %a.addr = alloca i32, align 4, !DIAssignID !13
+  call void @llvm.dbg.assign(metadata i1 undef, metadata !12, metadata !DIExpression(), metadata !13, metadata i32* %a.addr, metadata !DIExpression()), !dbg !14
+  call void @llvm.dbg.assign(metadata i1 undef, metadata !30, metadata !DIExpression(), metadata !13, metadata i32* %a.addr, metadata !DIExpression()), !dbg !14  
+  store i32 %a, i32* %a.addr, align 4, !tbaa !15, !DIAssignID !19
+  call void @llvm.dbg.assign(metadata i32 %a, metadata !12, metadata !DIExpression(), metadata !19, metadata i32* %a.addr, metadata !DIExpression()), !dbg !14
+  %0 = load i32, i32* %a.addr, align 4, !dbg !20, !tbaa !15
+  %tobool = icmp ne i32 %0, 0, !dbg !20
+  br i1 %tobool, label %if.then, label %if.else, !dbg !22
+
+if.then:                                          ; preds = %entry
+  %1 = load i32, i32* %a.addr, align 4, !dbg !23, !tbaa !15
+  %add = add nsw i32 %1, 1, !dbg !23
+  store i32 %add, i32* %a.addr, align 4, !dbg !23, !tbaa !15, !DIAssignID !24
+  call void @llvm.dbg.assign(metadata i32 %add, metadata !12, metadata !DIExpression(), metadata !24, metadata i32* %a.addr, metadata !DIExpression()), !dbg !14
+  br label %if.end, !dbg !25
+
+if.else:                                          ; preds = %entry
+  store i32 -1, i32* %a.addr, align 4, !dbg !26, !tbaa !15, !DIAssignID !27
+  call void @llvm.dbg.assign(metadata i32 -1, metadata !12, metadata !DIExpression(), metadata !27, metadata i32* %a.addr, metadata !DIExpression()), !dbg !14
+  br label %if.end
+
+if.end:                                           ; preds = %if.else, %if.then
+  %2 = load i32, i32* %a.addr, align 4, !dbg !28, !tbaa !15
+  ret i32 %2, !dbg !29
+}
+
+declare void @llvm.dbg.assign(metadata, metadata, metadata, metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2, !3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang version 14.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "test.cpp", directory: "/")
+!2 = !{i32 7, !"Dwarf Version", i32 5}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = !{i32 1, !"wchar_size", i32 4}
+!5 = !{i32 7, !"uwtable", i32 1}
+!6 = !{!"clang version 14.0.0"}
+!7 = distinct !DISubprogram(name: "f", linkageName: "_Z1fi", scope: !1, file: !1, line: 1, type: !8, scopeLine: 1, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !11)
+!8 = !DISubroutineType(types: !9)
+!9 = !{!10, !10}
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = !{!12}
+!12 = !DILocalVariable(name: "a", arg: 1, scope: !7, file: !1, line: 1, type: !10)
+!13 = distinct !DIAssignID()
+!14 = !DILocation(line: 0, scope: !7)
+!15 = !{!16, !16, i64 0}
+!16 = !{!"int", !17, i64 0}
+!17 = !{!"omnipotent char", !18, i64 0}
+!18 = !{!"Simple C++ TBAA"}
+!19 = distinct !DIAssignID()
+!20 = !DILocation(line: 2, column: 7, scope: !21)
+!21 = distinct !DILexicalBlock(scope: !7, file: !1, line: 2, column: 7)
+!22 = !DILocation(line: 2, column: 7, scope: !7)
+!23 = !DILocation(line: 3, column: 7, scope: !21)
+!24 = distinct !DIAssignID()
+!25 = !DILocation(line: 3, column: 5, scope: !21)
+!26 = !DILocation(line: 5, column: 7, scope: !21)
+!27 = distinct !DIAssignID()
+!28 = !DILocation(line: 6, column: 10, scope: !7)
+!29 = !DILocation(line: 6, column: 3, scope: !7)
+!30 = !DILocalVariable(name: "b", arg: 2, scope: !7, file: !1, line: 1, type: !10)

llvm/test/DebugInfo/Generic/assignment-tracking/mem2reg/single-block-alloca.ll

+; RUN: opt -passes=mem2reg -S %s -o - \
+; RUN: | FileCheck %s --implicit-check-not="call void @llvm.dbg"
+
+;; Test assignment tracking debug info when mem2reg promotes a single-block
+;; alloca. Check the output when the stores are tagged and also untagged (test
+;; manually updated for the latter by linking a dbg.assgin for another variable
+;; "b" to the alloca).
+
+; CHECK: entry:
+; CHECK-NEXT: call void @llvm.dbg.value(metadata i32 %a, metadata ![[B:[0-9]+]]
+; CHECK-NEXT: call void @llvm.dbg.assign(metadata i32 %a, metadata ![[A:[0-9]+]]
+; CHECK-NEXT: %add =
+; CHECK-NEXT: call void @llvm.dbg.value(metadata i32 %add, metadata ![[B]]
+; CHECK-NEXT: call void @llvm.dbg.assign(metadata i32 %add, metadata ![[A]]
+
+; CHECK-DAG: ![[A]] = !DILocalVariable(name: "a",
+; CHECK-DAG: ![[B]] = !DILocalVariable(name: "b",
+
+;; $ cat test.cpp
+;; int f(int a) {
+;;   a += 1;
+;;   return a;
+;; }
+
+define dso_local noundef i32 @_Z1fi(i32 noundef %a) !dbg !7 {
+entry:
+  %a.addr = alloca i32, align 4, !DIAssignID !13
+  call void @llvm.dbg.assign(metadata i1 undef, metadata !12, metadata !DIExpression(), metadata !13, metadata i32* %a.addr, metadata !DIExpression()), !dbg !14
+  call void @llvm.dbg.assign(metadata i1 undef, metadata !24, metadata !DIExpression(), metadata !13, metadata i32* %a.addr, metadata !DIExpression()), !dbg !14
+  store i32 %a, i32* %a.addr, align 4, !tbaa !15, !DIAssignID !19
+  call void @llvm.dbg.assign(metadata i32 %a, metadata !12, metadata !DIExpression(), metadata !19, metadata i32* %a.addr, metadata !DIExpression()), !dbg !14
+  %0 = load i32, i32* %a.addr, align 4, !dbg !20, !tbaa !15
+  %add = add nsw i32 %0, 1, !dbg !20
+  store i32 %add, i32* %a.addr, align 4, !dbg !20, !tbaa !15, !DIAssignID !21
+  call void @llvm.dbg.assign(metadata i32 %add, metadata !12, metadata !DIExpression(), metadata !21, metadata i32* %a.addr, metadata !DIExpression()), !dbg !14
+  %1 = load i32, i32* %a.addr, align 4, !dbg !22, !tbaa !15
+  ret i32 %1, !dbg !23
+}
+
+declare void @llvm.dbg.assign(metadata, metadata, metadata, metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2, !3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang version 14.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "test.cpp", directory: "/")
+!2 = !{i32 7, !"Dwarf Version", i32 5}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = !{i32 1, !"wchar_size", i32 4}
+!5 = !{i32 7, !"uwtable", i32 1}
+!6 = !{!"clang version 14.0.0"}
+!7 = distinct !DISubprogram(name: "f", linkageName: "_Z1fi", scope: !1, file: !1, line: 1, type: !8, scopeLine: 1, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !11)
+!8 = !DISubroutineType(types: !9)
+!9 = !{!10, !10}
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = !{!12}
+!12 = !DILocalVariable(name: "a", arg: 1, scope: !7, file: !1, line: 1, type: !10)
+!13 = distinct !DIAssignID()
+!14 = !DILocation(line: 0, scope: !7)
+!15 = !{!16, !16, i64 0}
+!16 = !{!"int", !17, i64 0}
+!17 = !{!"omnipotent char", !18, i64 0}
+!18 = !{!"Simple C++ TBAA"}
+!19 = distinct !DIAssignID()
+!20 = !DILocation(line: 2, column: 5, scope: !7)
+!21 = distinct !DIAssignID()
+!22 = !DILocation(line: 3, column: 10, scope: !7)
+!23 = !DILocation(line: 3, column: 3, scope: !7)
+!24 = !DILocalVariable(name: "b", arg: 1, scope: !7, file: !1, line: 1, type: !10)

llvm/test/DebugInfo/Generic/assignment-tracking/mem2reg/single-store-alloca.ll

+; RUN: opt -passes=mem2reg -S %s -o - \
+; RUN: | FileCheck %s --implicit-check-not="call void @llvm.dbg"
+
+;; Test assignment tracking debug info when mem2reg promotes a single-store
+;; alloca.
+
+; CHECK: entry:
+; CHECK-NEXT: call void @llvm.dbg.value(metadata i32 %a, metadata ![[B:[0-9]+]]
+; CHECK-NEXT: call void @llvm.dbg.assign(metadata i32 %a, metadata ![[A:[0-9]+]]
+; CHECK-NEXT: ret
+
+; CHECK-DAG: ![[A]] = !DILocalVariable(name: "a",
+; CHECK-DAG: ![[B]] = !DILocalVariable(name: "b",
+
+;; 1. using source:
+;; $ cat test.cpp
+;; int f(int a) { return a; }
+;; 2. with dbg.assign for another variable ("b") attached to a's alloca to
+;;    check that a dbg.value is generated for the variable to represent the
+;;    store despite the store not having a dbg.assign linked for it.
+
+; Function Attrs: mustprogress nounwind uwtable
+define dso_local noundef i32 @_Z1fi(i32 noundef %a) #0 !dbg !7 {
+entry:
+  %a.addr = alloca i32, align 4, !DIAssignID !13
+  call void @llvm.dbg.assign(metadata i1 undef, metadata !12, metadata !DIExpression(), metadata !13, metadata i32* %a.addr, metadata !DIExpression()), !dbg !14
+  call void @llvm.dbg.assign(metadata i1 undef, metadata !22, metadata !DIExpression(), metadata !13, metadata i32* %a.addr, metadata !DIExpression()), !dbg !14
+  store i32 %a, i32* %a.addr, align 4, !tbaa !15, !DIAssignID !19
+  call void @llvm.dbg.assign(metadata i32 %a, metadata !12, metadata !DIExpression(), metadata !19, metadata i32* %a.addr, metadata !DIExpression()), !dbg !14
+  %0 = load i32, i32* %a.addr, align 4, !dbg !20, !tbaa !15
+  ret i32 %0, !dbg !21
+}
+
+declare void @llvm.dbg.assign(metadata, metadata, metadata, metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2, !3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang version 14.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "test.cpp", directory: "/")
+!2 = !{i32 7, !"Dwarf Version", i32 5}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = !{i32 1, !"wchar_size", i32 4}
+!5 = !{i32 7, !"uwtable", i32 1}
+!6 = !{!"clang version 14.0.0)"}
+!7 = distinct !DISubprogram(name: "f", linkageName: "_Z1fi", scope: !1, file: !1, line: 1, type: !8, scopeLine: 1, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !11)
+!8 = !DISubroutineType(types: !9)
+!9 = !{!10, !10}
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = !{!12}
+!12 = !DILocalVariable(name: "a", arg: 1, scope: !7, file: !1, line: 1, type: !10)
+!13 = distinct !DIAssignID()
+!14 = !DILocation(line: 0, scope: !7)
+!15 = !{!16, !16, i64 0}
+!16 = !{!"int", !17, i64 0}
+!17 = !{!"omnipotent char", !18, i64 0}
+!18 = !{!"Simple C++ TBAA"}
+!19 = distinct !DIAssignID()
+!20 = !DILocation(line: 1, column: 23, scope: !7)
+!21 = !DILocation(line: 1, column: 16, scope: !7)
+!22 = !DILocalVariable(name: "b", arg: 1, scope: !7, file: !1, line: 1, type: !10)