[Assignment Tracking] Fix fragment error for some DSE-shortened stores

[Orlando]

Summary

shortenAssignment inserts dbg.assigns with fragments describing the dead part of a shortened store after each dbg.assign linked to the store.

Without this patch it doesn't take into account that the dead part of a shortened store may be outside the bounds of a variable of a linked dbg.assign. It also doesn't correctly account for a non-zero offset in the address modifying DIExpression of the dbg.assign (which is possible for fragments now even though whole variables currently cannot have a non-zero offset in their alloca).

Fix this by moving the dead slice into variable-space and performing an intersect of that adjusted slice with the existing fragment.

This fixes a verifier error reported when building fuchsia with assignment tracking enabled: https://ci.chromium.org/ui/p/fuchsia/builders/ci/clang_toolchain.ci.core.x64-release/b8784000953022145169/overview

[Orlando]

I've added a couple of inline comments into one of the test to help explain the changes.

llvm/test/DebugInfo/Generic/assignment-tracking/dse/dse-after-memcpyopt-merge.ll

16–21

Prior to the patch each dbg.assign with a fragment overlapping the dead part of the store would get an unlinked dbg.assign placed after it.

With this patch that is still done in most cases, but if the dead slice is exactly the same as the existing fragment the dbg.assign itself is just unlinked. That's why on the left we have 2 CHECKs for both of the overlapped dbg.assigns. On the right we have one for each, plus I added in the other 2 non-overlapped dbg.assigns to improve test coverage.

48

I removed these dbg.assigns to reduce test clutter as they're not needed.

[jmorse]

I guess we're finding all the twisty turney passages (all different) through the compiler that generate uncertainty over variable locations. On the one hand this is exactly what we want to be finding with assignment tracking, on the other hand it sucks that we're now needing to preserve so much detail. Discussed offline -- possibly the correct path is to relax the verifier requirements and just accept some imprecision (but not inaccuracy) in these intrinsics, it depends on whether this is the last corner case.

For this particular patch I think it's hard to track exactly what's going on given that there are now a bunch of different fragments flying around. Refactoring into some utilities in DebugInfoMetadata.cpp would be preferred to reduce the amount we're expanding the DSE file by, plus some ascii-art diagrams of exactly what fragments we're working with and manipulating. It's going to be hard to maintain in the future unless it's very plain. IMO as the terms "variable space" and "dest space" don't show up elsewhere in assignment tracking some more standardised nomenclature should be found.

llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp

492–509

Could you elaborate on what these terms mean here (not clear to me)

517–523

I feel there's not enough (mental) context here to work out what's going on -- relative to what?

530–531

Just to make me feel better, could you make the SmallVector a named variable please, simply for ease of reading.

llvm/test/DebugInfo/Generic/assignment-tracking/dse/shorten.ll

45

Reason for deleting these?

[Orlando]

In D148536#4277449, @jmorse wrote:

I guess we're finding all the twisty turney passages (all different) through the compiler that generate uncertainty over variable locations. On the one hand this is exactly what we want to be finding with assignment tracking, on the other hand it sucks that we're now needing to preserve so much detail. Discussed offline -- possibly the correct path is to relax the verifier requirements and just accept some imprecision (but not inaccuracy) in these intrinsics, it depends on whether this is the last corner case.

For this particular patch I think it's hard to track exactly what's going on given that there are now a bunch of different fragments flying around. Refactoring into some utilities in DebugInfoMetadata.cpp would be preferred to reduce the amount we're expanding the DSE file by, plus some ascii-art diagrams of exactly what fragments we're working with and manipulating. It's going to be hard to maintain in the future unless it's very plain. IMO as the terms "variable space" and "dest space" don't show up elsewhere in assignment tracking some more standardised nomenclature should be found.

Thank you for reviewing this. I've moved the functions to more appropriate places outside of DeadStoreElimination.cpp, addressed the nits, and added a large comment to the body of calculateFragmentIntersect. wdyt? I could probably chop the first paragraphs before # Example 1 out, but the additional context may be useful?

[jmorse]

Cool, that's a lot easier to understand now -- it's a verbose comment block, but vital for understanding the full context of what's going on for future readers.

Again, this is a gnarly corner but let's hope it's a final one. I've got a curiosity comment, one grammar comment added plus an outstanding one on shorten.ll, but I think this is good to go in.

llvm/include/llvm/IR/DebugInfo.h

227–235

Is there a meaningful distinction between a zero-sized fragment and returning false? (just curious)

llvm/lib/IR/DebugInfo.cpp

1816

[paulkirth]

Overall I think this looks fine, so thanks for addressing the issue. I had one small comment and one question I left inline.

Also, the issue was found building Fuchsia. We share infrastructure w/ Chromium, so the URL may have been misleading.

You shouldn't consider any of these blocking.

llvm/lib/IR/DebugInfo.cpp

1797–1800

Why does this take an optional<> as an output argument and return bool? wouldn't it make more sense to just return an optional<>?

1902

I know isPointerOffset() isn't part of this patch, but it's very surprising to find out that it doesn't return bool.

[Orlando]

Thank you both for the reviews!

Also, the issue was found building Fuchsia. We share infrastructure w/ Chromium, so the URL may have been misleading.

Aha, I see, I will fix that in the commit message, thanks.

llvm/include/llvm/IR/DebugInfo.h

227–235

Yeah - if the intersect can't be calculated for some reason you may wish to do something different (defensive/safe). Here's the code from DeadStoreElimination:

if (!at::calculateFragmentIntersect(DL, OriginalDest, DeadSliceOffsetInBits,
                                    DeadSliceSizeInBits, DAI,
                                    NewFragment) ||
    !NewFragment) {
  // We couldn't calculate the intersecting fragment for some reason. Be
  // cautious and unlink the whole assignment from the store.
  DAI->setKillAddress();
  DAI->setAssignId(GetDeadLink());
  continue;
}
// No intersect.
if (NewFragment->SizeInBits == 0)
  continue;

In this case we unlink the existing dbg.assign if the intersect couldn't be calculated (return false) to be "safe", or if the entire intersected fragment == the existing fragment (NewFragment == nullopt). In the case of no intersect (NewFragment->SizeInBits == 0) we don't do anything to the the dbg.assign, nor insert any new ones.

llvm/lib/IR/DebugInfo.cpp

1797–1800

It does feel a bit clunky but I wanted to distinguish between "the entire fragment or variable from DAI" (Result == nullopt) and "the intersect couldn't be calculated for some reason" (return false).

Using nullopt to represent the entire fragment or variable from DAI isn't completely weird because debug intrinsics containing no fragment info in their DIExpressions are considered to represent a location for the entire variable, and DIExpression::getFragment returns an optional<>.

Returning optional<> would result in a less clunky interface here. We'd have to move the "is the fragment the same size as DAI's fragment or variable" check done by the caller after instead (which is not unreasonable).

As you said you didn't intend your comments to be blocking please let me know if you'd like to see this change and I'll happily create another patch.

1902

It does feel like the name is slightly misleading. Maybe getPointerOffset would make more sense.

llvm/test/DebugInfo/Generic/assignment-tracking/dse/shorten.ll

45

Ah I forgot to submit this inline comment after updating the patch. My reasoning was that I was in the neighbourhood, reading the test, dealing with failures while working on my patch. The lifetime intrinsics don't add anything and just clutter the tests. I've left the change out of this patch - I can always make the change separately.

[hokein]

I was trying to fix the bazel failure https://buildkite.com/llvm-project/upstream-bazel/builds/59967#01879985-8d44-4041-9cd0-a1e41371208e (by adding the :Analysis dep to Core target), and discovered that this patch introduces a cyclic dependency between Core and Analysis:

$ bazel build --config=generic_clang @llvm-project//clang/unittests:ast_matchers_tests

Starting local Bazel server and connecting to it...
project//llvm:Analysis: cycle in dependency graph:
    @llvm-project//clang/unittests:ast_matchers_tests (940e5bfa4f289f5f81247f8a14276f4ff7b178b294d993a599b7dcdd4938fb45)
    @llvm-project//clang:ast (9e8b7842809f71769ff4024fa8ff44105697d8cd0cb0a5bcaa4aede8f4e50ff3)
    @llvm-project//clang:basic (9e8b7842809f71769ff4024fa8ff44105697d8cd0cb0a5bcaa4aede8f4e50ff3)
    @llvm-project//llvm:Instrumentation (9e8b7842809f71769ff4024fa8ff44105697d8cd0cb0a5bcaa4aede8f4e50ff3)
    @llvm-project//llvm:TransformUtils (9e8b7842809f71769ff4024fa8ff44105697d8cd0cb0a5bcaa4aede8f4e50ff3)
.-> @llvm-project//llvm:Analysis (9e8b7842809f71769ff4024fa8ff44105697d8cd0cb0a5bcaa4aede8f4e50ff3)
|   @llvm-project//llvm:Object (9e8b7842809f71769ff4024fa8ff44105697d8cd0cb0a5bcaa4aede8f4e50ff3)
|   @llvm-project//llvm:IRReader (9e8b7842809f71769ff4024fa8ff44105697d8cd0cb0a5bcaa4aede8f4e50ff3)
|   @llvm-project//llvm:AsmParser (9e8b7842809f71769ff4024fa8ff44105697d8cd0cb0a5bcaa4aede8f4e50ff3)
|   @llvm-project//llvm:Core (9e8b7842809f71769ff4024fa8ff44105697d8cd0cb0a5bcaa4aede8f4e50ff3)
`-- @llvm-project//llvm:Analysis (9e8b7842809f71769ff4024fa8ff44105697d8cd0cb0a5bcaa4aede8f4e50ff3)

The DebugInfo.cpp (in Core target) uses the functions from llvm/Analysis/ValueTracking.h (in Analysis target), thus Core target should depend on Analysis (we should probably add the Analysis dep to LLVMCore target in the cmake as well), but Analysis already
depends on Core.

[Orlando]

Hi @hokein, thanks for this info.

The library dependency issue was fixed in D148698 which moves the functions needed by DebugInfo.cpp into LLVMCore (in Value.h). I fixed the bazel-build include issue by removing (the now unused / unneeded) #include llvm/Analysis/ValueTracking.h from DebugInfo.cpp in 04452e83ded9bfca0ff272fae9c537dde028daf2.

[hokein]

In D148536#4280443, @Orlando wrote:

Hi @hokein, thanks for this info.

The library dependency issue was fixed in D148698 which moves the functions needed by DebugInfo.cpp into LLVMCore (in Value.h). I fixed the bazel-build include issue by removing (the now unused / unneeded) #include llvm/Analysis/ValueTracking.h from DebugInfo.cpp in 04452e83ded9bfca0ff272fae9c537dde028daf2.

Great, thanks for the fix!

llvm/include/llvm/IR/DebugInfo.h

 void deleteAssignmentMarkers(const Instruction *Inst);
 
 /// Replace all uses (and attachments) of \p Old with \p New.
 void RAUW(DIAssignID *Old, DIAssignID *New);
 
 /// Remove all Assignment Tracking related intrinsics and metadata from \p F.
 void deleteAll(Function *F);
 
+/// Calculate the fragment of the variable in \p DAI covered
+/// from (Dest + SliceOffsetInBits) to
+///   to (Dest + SliceOffsetInBits + SliceSizeInBits)
+///
+/// Return false if it can't be calculated for any reason.
+/// Result is set to nullopt if the intersect equals the variable fragment (or
+/// variable size) in DAI.
+///
+/// Result contains a zero-sized fragment if there's no intersect.
+bool calculateFragmentIntersect(
+    const DataLayout &DL, const Value *Dest, uint64_t SliceOffsetInBits,
+    uint64_t SliceSizeInBits, const DbgAssignIntrinsic *DAI,
+    std::optional<DIExpression::FragmentInfo> &Result);
+
 /// Helper struct for trackAssignments, below. We don't use the similar
 /// DebugVariable class because trackAssignments doesn't (yet?) understand
 /// partial variables (fragment info) as input and want to make that clear and
 /// explicit using types. In addition, eventually we will want to understand
 /// expressions that modify the base address too, which a DebugVariable doesn't
 /// capture.
 struct VarRecord {
   DILocalVariable *Var;

llvm/include/llvm/IR/DebugInfoMetadata.h

FragmentInfo(uint64_t SizeInBits, uint64_t OffsetInBits)
         : SizeInBits(SizeInBits), OffsetInBits(OffsetInBits) {}
     uint64_t SizeInBits;
     uint64_t OffsetInBits;
     /// Return the index of the first bit of the fragment.
     uint64_t startInBits() const { return OffsetInBits; }
     /// Return the index of the bit after the end of the fragment, e.g. for
     /// fragment offset=16 and size=32 return their sum, 48.
     uint64_t endInBits() const { return OffsetInBits + SizeInBits; }
+
+    /// Returns a zero-sized fragment if A and B don't intersect.
+    static DIExpression::FragmentInfo intersect(DIExpression::FragmentInfo A,
+                                                DIExpression::FragmentInfo B) {
+      uint64_t StartInBits = std::max(A.OffsetInBits, B.OffsetInBits);
+      uint64_t EndInBits = std::min(A.endInBits(), B.endInBits());
+      if (EndInBits <= StartInBits)
+        return {0, 0};
+      return DIExpression::FragmentInfo(EndInBits - StartInBits, StartInBits);
+    }
   };
 
   /// Retrieve the details of this fragment expression.
   static std::optional<FragmentInfo> getFragmentInfo(expr_op_iterator Start,
                                                      expr_op_iterator End);
 
   /// Retrieve the details of this fragment expression.
   std::optional<FragmentInfo> getFragmentInfo() const {

llvm/include/llvm/IR/IntrinsicInst.h

public:
   /// is described.
   std::optional<uint64_t> getFragmentSizeInBits() const;
 
   /// Get the FragmentInfo for the variable.
   std::optional<DIExpression::FragmentInfo> getFragment() const {
     return getExpression()->getFragmentInfo();
   }
 
+  /// Get the FragmentInfo for the variable if it exists, otherwise return a
+  /// FragmentInfo that covers the entire variable if the variable size is
+  /// known, otherwise return a zero-sized fragment.
+  DIExpression::FragmentInfo getFragmentOrEntireVariable() const {
+    DIExpression::FragmentInfo VariableSlice(0, 0);
+    // Get the fragment or variable size, or zero.
+    if (auto Sz = getFragmentSizeInBits())
+      VariableSlice.SizeInBits = *Sz;
+    if (auto Frag = getExpression()->getFragmentInfo())
+      VariableSlice.OffsetInBits = Frag->OffsetInBits;
+    return VariableSlice;
+  }
+
   /// \name Casting methods
   /// @{
   static bool classof(const IntrinsicInst *I) {
     switch (I->getIntrinsicID()) {
     case Intrinsic::dbg_declare:
     case Intrinsic::dbg_value:
     case Intrinsic::dbg_assign:
       return true;

llvm/lib/IR/DebugInfo.cpp

 #include "llvm-c/DebugInfo.h"
 #include "LLVMContextImpl.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
+#include "llvm/Analysis/ValueTracking.h"
 #include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/DIBuilder.h"
 #include "llvm/IR/DebugInfo.h"
 #include "llvm/IR/DebugInfoMetadata.h"
 #include "llvm/IR/DebugLoc.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/GVMaterializer.h"
for (Instruction &I : BB) {
       else
         I.setMetadata(LLVMContext::MD_DIAssignID, nullptr);
     }
   }
   for (auto *DAI : ToDelete)
     DAI->eraseFromParent();
 }
 
+bool at::calculateFragmentIntersect(
+    const DataLayout &DL, const Value *Dest, uint64_t SliceOffsetInBits,
+    uint64_t SliceSizeInBits, const DbgAssignIntrinsic *DAI,
+    std::optional<DIExpression::FragmentInfo> &Result) {
+  // There are multiple offsets at play in this function, so let's break it
+  // down. Starting with how variables may be stored in allocas:
+  //
+  //   1 Simplest case: variable is alloca sized and starts at offset 0.
+  //   2 Variable is larger than the alloca: the alloca holds just a part of it.
+  //   3 Variable is smaller than the alloca: the alloca may hold multiple
+  //   variables.
+  //
+  // Imagine we have a store to the entire alloca. In case (3) the store
+  // affects bits outside of the bounds of each variable. In case (2), where
+  // the alloca holds the Xth bit to the Yth bit of a variable, the
+  // zero-offset store doesn't represent an assignment at offset zero to the
+  // variable. It is an assignment to offset X.
+  //
+  // # Example 1
+  // Obviously, not all stores are alloca-sized have zero offset. Imagine the
+  // lower 32 bits of this store are dead and are going to be DSEd:
+  //
+  //    store i64 %v, ptr %dest, !DIAssignID !1
+  //    dbg.assign(..., !DIExpression(fragment, 128, 32), !1, %dest,
+  //               !DIExpression(DW_OP_plus_uconst, 4))
+  //
+  // Goal: Given our dead bits at offset:0 size:32 for the store, determine the
+  // part of the variable, which fits in the fragment expressed by the
+  // dbg.assign, that has been killed, if any.
+  //
+  //     calculateFragmentIntersect(..., SliceOffsetInBits=0,
+  //                 SliceSizeInBits=32, Dest=%dest, DAI=dbg.assign)
+  //
+  // Drawing the store (s) in memory followed by the shortened version ($),
+  // then the dbg.assign (d), with the fragment information on a seperate scale
+  // underneath:
+  //
+  // Memory
+  // offset
+  //   from
+  //   dest 0      63
+  //        |      |
+  //       s[######] - Original stores 64 bits to Dest.
+  //       $----[##] - DSE says the lower 32 bits are dead, to be removed.
+  //       d    [##] - DAI's address-modifying expression adds 4 bytes to dest.
+  // Variable   |  |
+  // Fragment   128|
+  //  Offsets      159
+  //
+  // The answer is achieved in a few steps:
+  // 1. Add the fragment offset to the store offset:
+  //      SliceOffsetInBits:0 + VarFrag.OffsetInBits:128 = 128
+  //
+  // 2. Subtract the address-modifying expression offset plus difference
+  //    between d.address and dest:
+  //      128 - (expression_offset:32 + (d.address - dest):0) = 96
+  //
+  // 3. That offset along with the store size (32) represents the bits of the
+  //    variable that'd be affected by the store. Call it SliceOfVariable.
+  //    Intersect that with DAI's fragment info:
+  //      SliceOfVariable ∩ DAI_fragment = none
+  //
+  // In this case: none of the dead bits of the store affect DAI.
+  //
+  // # Example 2
+  // Similar example with the same goal. This time the upper 16 bits
+  // of the store are going to be DSE'd.
+  //
+  //    store i64 %v, ptr %dest, !DIAssignID !1
+  //    dbg.assign(..., !DIExpression(fragment, 128, 32), !1, %dest,
+  //               !DIExpression(DW_OP_plus_uconst, 4))
+  //
+  //     calculateFragmentIntersect(..., SliceOffsetInBits=48,
+  //                 SliceSizeInBits=16, Dest=%dest, DAI=dbg.assign)
+  //
+  // Memory
+  // offset
+  //   from
+  //   dest 0      63
+  //        |      |
+  //       s[######] - Original stores 64 bits to Dest.
+  //       $[####]-- - DSE says the upper 16 bits are dead, to be removed.
+  //       d    [##] - DAI's address-modifying expression adds 4 bytes to dest.
+  // Variable   |  |
+  // Fragment   128|
+  //  Offsets      159
+  //
+  // Using the same steps in the first example:
+  // 1. SliceOffsetInBits:48 + VarFrag.OffsetInBits:128 = 176
+  // 2. 176 - (expression_offset:32 + (d.address - dest):0) = 144
+  // 3. SliceOfVariable offset = 144, size = 16:
+  //      SliceOfVariable ∩ DAI_fragment = (offset: 144, size: 16)
+  // SliceOfVariable tells us the bits of the variable described by DAI that are
+  // affected by the DSE.
+  if (DAI->isKillAddress())
+    return false;
+
+  DIExpression::FragmentInfo VarFrag = DAI->getFragmentOrEntireVariable();
+  if (VarFrag.SizeInBits == 0)
+    return false; // Variable size is unknown.
+
+  // Calculate the difference between Dest and the dbg.assign address +
+  // address-modifying expression.
+  int64_t PointerOffsetInBits;
+  {
+    auto DestOffsetInBytes = llvm::isPointerOffset(Dest, DAI->getAddress(), DL);
+    if (!DestOffsetInBytes)
+      return false; // Can't calculate difference in addresses.
+
+    int64_t ExprOffsetInBytes;
+    if (!DAI->getAddressExpression()->extractIfOffset(ExprOffsetInBytes))
+      return false;
+
+    int64_t PointerOffsetInBytes = *DestOffsetInBytes + ExprOffsetInBytes;
+    PointerOffsetInBits = PointerOffsetInBytes * 8;
+  }
+
+  // Adjust the slice offset so that we go from describing the a slice
+  // of memory to a slice of the variable.
+  int64_t NewOffsetInBits =
+      SliceOffsetInBits + VarFrag.OffsetInBits - PointerOffsetInBits;
+  if (NewOffsetInBits < 0)
+    return false; // Fragment offsets can only be positive.
+  DIExpression::FragmentInfo SliceOfVariable(SliceSizeInBits, NewOffsetInBits);
+  // Intersect the variable slice with DAI's fragment to trim it down to size.
+  DIExpression::FragmentInfo TrimmedSliceOfVariable =
+      DIExpression::FragmentInfo::intersect(SliceOfVariable, VarFrag);
+  if (TrimmedSliceOfVariable == VarFrag)
+    Result = std::nullopt;
+  else
+    Result = TrimmedSliceOfVariable;
+  return true;
+}
+
 /// Collect constant properies (base, size, offset) of \p StoreDest.
 /// Return std::nullopt if any properties are not constants.
 static std::optional<AssignmentInfo>
 getAssignmentInfoImpl(const DataLayout &DL, const Value *StoreDest,
                       uint64_t SizeInBits) {
   APInt GEPOffset(DL.getIndexTypeSizeInBits(StoreDest->getType()), 0);
   const Value *Base = StoreDest->stripAndAccumulateConstantOffsets(
       DL, GEPOffset, /*AllowNonInbounds*/ true);

llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp

if (B != FirstBB) {
         }
         WorkList.push_back(std::make_pair(Pred, PredAddr));
       }
     }
   }
   return true;
 }
 
-static void shortenAssignment(Instruction *Inst, uint64_t OldOffsetInBits,
-                              uint64_t OldSizeInBits, uint64_t NewSizeInBits,
-                              bool IsOverwriteEnd) {
-  DIExpression::FragmentInfo DeadFragment;
-  DeadFragment.SizeInBits = OldSizeInBits - NewSizeInBits;
-  DeadFragment.OffsetInBits =
+static void shortenAssignment(Instruction *Inst, Value *OriginalDest,
+                              uint64_t OldOffsetInBits, uint64_t OldSizeInBits,
+                              uint64_t NewSizeInBits, bool IsOverwriteEnd) {
+  const DataLayout &DL = Inst->getModule()->getDataLayout();
+  uint64_t DeadSliceSizeInBits = OldSizeInBits - NewSizeInBits;
+  uint64_t DeadSliceOffsetInBits =
       OldOffsetInBits + (IsOverwriteEnd ? NewSizeInBits : 0);
-
-  auto CreateDeadFragExpr = [Inst, DeadFragment]() {
-    // FIXME: This should be using the DIExpression in the Alloca's dbg.assign
-    // for the variable, since that could also contain a fragment?
-    return *DIExpression::createFragmentExpression(
-        DIExpression::get(Inst->getContext(), std::nullopt),
+  auto SetDeadFragExpr = [](DbgAssignIntrinsic *DAI,
+                            DIExpression::FragmentInfo DeadFragment) {
+    // createFragmentExpression expects an offset relative to the existing
+    // fragment offset if there is one.
+    uint64_t RelativeOffset = DeadFragment.OffsetInBits -
+                              DAI->getExpression()
+                                  ->getFragmentInfo()
+                                  .value_or(DIExpression::FragmentInfo(0, 0))
+                                  .OffsetInBits;
+    if (auto NewExpr = DIExpression::createFragmentExpression(
+            DAI->getExpression(), RelativeOffset, DeadFragment.SizeInBits)) {
+      DAI->setExpression(*NewExpr);
+      return;
+    }
+    // Failed to create a fragment expression for this so discard the value,
+    // making this a kill location.
+    auto *Expr = *DIExpression::createFragmentExpression(
+        DIExpression::get(DAI->getContext(), std::nullopt),
         DeadFragment.OffsetInBits, DeadFragment.SizeInBits);
+    DAI->setExpression(Expr);
+    DAI->setKillLocation();
   };
 
   // A DIAssignID to use so that the inserted dbg.assign intrinsics do not
   // link to any instructions. Created in the loop below (once).
   DIAssignID *LinkToNothing = nullptr;
+  LLVMContext &Ctx = Inst->getContext();
+  auto GetDeadLink = [&Ctx, &LinkToNothing]() {
+    if (!LinkToNothing)
+      LinkToNothing = DIAssignID::getDistinct(Ctx);
+    return LinkToNothing;
+  };
 
   // Insert an unlinked dbg.assign intrinsic for the dead fragment after each
-  // overlapping dbg.assign intrinsic.
-  for (auto *DAI : at::getAssignmentMarkers(Inst)) {
-    if (auto FragInfo = DAI->getExpression()->getFragmentInfo()) {
-      if (!DIExpression::fragmentsOverlap(*FragInfo, DeadFragment))
-        continue;
+  // overlapping dbg.assign intrinsic. The loop invalidates the iterators
+  // returned by getAssignmentMarkers so save a copy of the markers to iterate
+  // over.
+  auto LinkedRange = at::getAssignmentMarkers(Inst);
+  SmallVector<DbgAssignIntrinsic *> Linked(LinkedRange.begin(),
+                                           LinkedRange.end());
+  for (auto *DAI : Linked) {
+    std::optional<DIExpression::FragmentInfo> NewFragment;
+    if (!at::calculateFragmentIntersect(DL, OriginalDest, DeadSliceOffsetInBits,
+                                        DeadSliceSizeInBits, DAI,
+                                        NewFragment) ||
+        !NewFragment) {
+      // We couldn't calculate the intersecting fragment for some reason. Be
+      // cautious and unlink the whole assignment from the store.
+      DAI->setKillAddress();
+      DAI->setAssignId(GetDeadLink());
     }
+    // No intersect.
+    if (NewFragment->SizeInBits == 0)
+      continue;
 
     // Fragments overlap: insert a new dbg.assign for this dead part.
     auto *NewAssign = cast<DbgAssignIntrinsic>(DAI->clone());
     NewAssign->insertAfter(DAI);
-    if (!LinkToNothing)
-      LinkToNothing = DIAssignID::getDistinct(Inst->getContext());
-    NewAssign->setAssignId(LinkToNothing);
-    NewAssign->setExpression(CreateDeadFragExpr());
+    NewAssign->setAssignId(GetDeadLink());
+    if (NewFragment)
+      SetDeadFragExpr(NewAssign, *NewFragment);
     NewAssign->setKillAddress();
   }
 }
 
 static bool tryToShorten(Instruction *DeadI, int64_t &DeadStart,
                          uint64_t &DeadSize, int64_t KillingStart,
                          uint64_t KillingSize, bool IsOverwriteEnd) {
   auto *DeadIntrinsic = cast<AnyMemIntrinsic>(DeadI);
LLVM_DEBUG(dbgs() << "DSE: Remove Dead Store:\n  OW "
                     << "\n  KILLER [" << ToRemoveStart << ", "
                     << int64_t(ToRemoveStart + ToRemoveSize) << ")\n");
 
   Value *DeadWriteLength = DeadIntrinsic->getLength();
   Value *TrimmedLength = ConstantInt::get(DeadWriteLength->getType(), NewSize);
   DeadIntrinsic->setLength(TrimmedLength);
   DeadIntrinsic->setDestAlignment(PrefAlign);
 
-  if (!IsOverwriteEnd) {
-    Value *OrigDest = DeadIntrinsic->getRawDest();
+  if (!IsOverwriteEnd) {
     Type *Int8PtrTy =
         Type::getInt8PtrTy(DeadIntrinsic->getContext(),
                            OrigDest->getType()->getPointerAddressSpace());
     Value *Dest = OrigDest;
     if (OrigDest->getType() != Int8PtrTy)
       Dest = CastInst::CreatePointerCast(OrigDest, Int8PtrTy, "", DeadI);
     Value *Indices[1] = {
         ConstantInt::get(DeadWriteLength->getType(), ToRemoveSize)};
     Instruction *NewDestGEP = GetElementPtrInst::CreateInBounds(
         Type::getInt8Ty(DeadIntrinsic->getContext()), Dest, Indices, "", DeadI);
     NewDestGEP->setDebugLoc(DeadIntrinsic->getDebugLoc());
     if (NewDestGEP->getType() != OrigDest->getType())
       NewDestGEP = CastInst::CreatePointerCast(NewDestGEP, OrigDest->getType(),
                                                "", DeadI);
     DeadIntrinsic->setDest(NewDestGEP);
   }
 
   // Update attached dbg.assign intrinsics. Assume 8-bit byte.
-  shortenAssignment(DeadI, DeadStart * 8, DeadSize * 8, NewSize * 8,
+  shortenAssignment(DeadI, OrigDest, DeadStart * 8, DeadSize * 8, NewSize * 8,
                     IsOverwriteEnd);
 
   // Finally update start and size of dead access.
   if (!IsOverwriteEnd)
     DeadStart += ToRemoveSize;
   DeadSize = NewSize;
 
   return true;

llvm/lib/Transforms/Scalar/SROA.cpp

 
 /// Calculate the fragment of a variable to use when slicing a store
 /// based on the slice dimensions, existing fragment, and base storage
 /// fragment.
 /// Results:
 /// UseFrag - Use Target as the new fragment.
 /// UseNoFrag - The new slice already covers the whole variable.
 /// Skip - The new alloca slice doesn't include this variable.
+/// FIXME: Can we use calculateFragmentIntersect instead?
 enum FragCalcResult { UseFrag, UseNoFrag, Skip };
 static FragCalcResult
 calculateFragment(DILocalVariable *Variable,
                   uint64_t NewStorageSliceOffsetInBits,
                   uint64_t NewStorageSliceSizeInBits,
                   std::optional<DIExpression::FragmentInfo> StorageFragment,
                   std::optional<DIExpression::FragmentInfo> CurrentFragment,
                   DIExpression::FragmentInfo &Target) {

llvm/test/DebugInfo/Generic/assignment-tracking/dse/dse-after-memcpyopt-merge.ll

-; RUN: opt %s -S -passes=dse -o - | FileCheck %s
+; RUN: opt %s -S -passes=dse -o - | FileCheck %s --implicit-check-not="call void @llvm.dbg"
 
 ;; Observed in the wild, but test is created by running memcpyopt on
 ;; assignment-tracking/memcpyopt/merge-stores.ll then manually inserting
 ;; two stores that overwrite each end of the memset.
 ;;
 ;; A memory intrinsic (or vector instruction) might have multiple dbg.assigns
 ;; linked to it if it has been created as a result of merging scalar stores,
 ;; such as in this example. DSE is going to shorten the memset because there's
-;; a later store that overwrites part of it. Insert a linked dbg.assign after
-;; each overlapping fragment to undef the dead part's memory location without
-;; needing to work out how to split the fragments exactly.
+;; a later store that overwrites part of it. Unlink the dbg.assigns that
+;; describe the overlapping fragments.
 
 ;; Check that there's an unlinked dbg.assign inserted after each overlapping
 ;; fragment of the shortened store.
 ;;
-; CHECK:      call void @llvm.dbg.assign(metadata float 0.000000e+00, metadata ![[VAR:[0-9]+]], metadata !DIExpression(DW_OP_LLVM_fragment, 0, 32), metadata ![[ID:[0-9]+]], metadata ptr %arrayidx5.i, metadata !DIExpression())
-; CHECK-NEXT: call void @llvm.dbg.assign(metadata float 0.000000e+00, metadata ![[VAR]], metadata !DIExpression(DW_OP_LLVM_fragment, 0, 32), metadata ![[UniqueID1:[0-9]+]], metadata ptr undef, metadata !DIExpression())
-
-; CHECK:      call void @llvm.dbg.assign(metadata float 0.000000e+00, metadata ![[VAR]], metadata !DIExpression(DW_OP_LLVM_fragment, 96, 32), metadata ![[ID]], metadata ptr %arrayidx7.i, metadata !DIExpression())
-; CHECK-NEXT: call void @llvm.dbg.assign(metadata float 0.000000e+00, metadata ![[VAR]], metadata !DIExpression(DW_OP_LLVM_fragment, 96, 32), metadata ![[UniqueID2:[0-9]+]], metadata ptr undef, metadata !DIExpression())
-
+; CHECK: llvm.dbg.assign({{.*}}, metadata ptr %g, metadata !DIExpression())
+; CHECK: llvm.dbg.assign(metadata float 0.000000e+00, metadata ![[#]], metadata !DIExpression(DW_OP_LLVM_fragment, 64, 32), metadata ![[ID:[0-9]+]], metadata ptr %arrayidx.i, metadata !DIExpression())
+; CHECK: llvm.dbg.assign(metadata float 0.000000e+00, metadata ![[#]], metadata !DIExpression(DW_OP_LLVM_fragment, 32, 32), metadata ![[ID]], metadata ptr %arrayidx3.i, metadata !DIExpression())
+; CHECK: llvm.dbg.assign(metadata float 0.000000e+00, metadata ![[#]], metadata !DIExpression(DW_OP_LLVM_fragment, 0, 32), metadata ![[UniqueID1:[0-9]+]], metadata ptr undef, metadata !DIExpression())
+; CHECK: llvm.dbg.assign(metadata float 0.000000e+00, metadata ![[#]], metadata !DIExpression(DW_OP_LLVM_fragment, 96, 32), metadata ![[UniqueID2:[0-9]+]], metadata ptr undef, metadata !DIExpression())
 ; CHECK: call void @llvm.memset{{.*}}, !DIAssignID ![[ID]]
 
 ; CHECK-DAG: ![[ID]] = distinct !DIAssignID()
 ; CHECK-DAG: ![[UniqueID1]] = distinct !DIAssignID()
 ; CHECK-DAG: ![[UniqueID2]] = distinct !DIAssignID()
 
 %struct.v = type { [4 x float] }
 
 $_ZN1vC2Ef = comdat any
 
 define dso_local void @_Z1fv() local_unnamed_addr !dbg !7 {
 entry:
   %g = alloca %struct.v, align 4, !DIAssignID !23
   call void @llvm.dbg.assign(metadata i1 undef, metadata !11, metadata !DIExpression(), metadata !23, metadata ptr %g, metadata !DIExpression()), !dbg !24
-  call void @llvm.lifetime.start.p0i8(i64 16, ptr nonnull %g), !dbg !25
-  call void @llvm.dbg.assign(metadata ptr %g, metadata !26, metadata !DIExpression(), metadata !35, metadata ptr undef, metadata !DIExpression()), !dbg !32
-  call void @llvm.dbg.assign(metadata float 0.000000e+00, metadata !29, metadata !DIExpression(), metadata !36, metadata ptr undef, metadata !DIExpression()), !dbg !32
    %arrayidx.i = getelementptr inbounds %struct.v, ptr %g, i64 0, i32 0, i64 2, !dbg !37
   call void @llvm.dbg.assign(metadata float 0.000000e+00, metadata !11, metadata !DIExpression(DW_OP_LLVM_fragment, 64, 32), metadata !39, metadata ptr %arrayidx.i, metadata !DIExpression()), !dbg !24
   %arrayidx3.i = getelementptr inbounds %struct.v, ptr %g, i64 0, i32 0, i64 1, !dbg !40
   call void @llvm.dbg.assign(metadata float 0.000000e+00, metadata !11, metadata !DIExpression(DW_OP_LLVM_fragment, 32, 32), metadata !39, metadata ptr %arrayidx3.i, metadata !DIExpression()), !dbg !24
   %arrayidx5.i = getelementptr inbounds %struct.v, ptr %g, i64 0, i32 0, i64 0, !dbg !41
   call void @llvm.dbg.assign(metadata float 0.000000e+00, metadata !11, metadata !DIExpression(DW_OP_LLVM_fragment, 0, 32), metadata !39, metadata ptr %arrayidx5.i, metadata !DIExpression()), !dbg !24
   %arrayidx7.i = getelementptr inbounds %struct.v, ptr %g, i64 0, i32 0, i64 3, !dbg !42
   call void @llvm.dbg.assign(metadata float 0.000000e+00, metadata !11, metadata !DIExpression(DW_OP_LLVM_fragment, 96, 32), metadata !39, metadata ptr %arrayidx7.i, metadata !DIExpression()), !dbg !24
   %0 = bitcast ptr %arrayidx5.i to ptr, !dbg !43
   call void @llvm.memset.p0i8.i64(ptr align 4 %0, i8 0, i64 16, i1 false), !dbg !44, !DIAssignID !39
   ;; -- Start modification
   %arrayidx7 = getelementptr inbounds %struct.v, ptr %g, i64 0, i32 0, i64 3, !dbg !24
   store float 0.000000e+00, ptr %arrayidx7, align 4, !dbg !24, !DIAssignID !49
-  call void @llvm.dbg.assign(metadata float 0.000000e+00, metadata !11, metadata !DIExpression(DW_OP_LLVM_fragment, 96, 32), metadata !49, metadata ptr %arrayidx7, metadata !DIExpression()), !dbg !24
   %arrayidx = getelementptr inbounds %struct.v, ptr %g, i64 0, i32 0, i64 0, !dbg !24
   store float 0.000000e+00, ptr %arrayidx, align 4, !dbg !24, !DIAssignID !50
-  call void @llvm.dbg.assign(metadata float 0.000000e+00, metadata !11, metadata !DIExpression(DW_OP_LLVM_fragment, 0, 32), metadata !50, metadata ptr %arrayidx, metadata !DIExpression()), !dbg !24
   ;; -- End modification
   call void @_Z3escP1v(ptr nonnull %g), !dbg !43
-  call void @llvm.lifetime.end.p0i8(i64 16, ptr nonnull %0), !dbg !45
   ret void, !dbg !45
 }
 
-declare void @llvm.lifetime.start.p0i8(i64 immarg, ptr nocapture)
 declare !dbg !64 dso_local void @_Z3escP1v(ptr) local_unnamed_addr
-declare void @llvm.lifetime.end.p0i8(i64 immarg, ptr nocapture)
 declare void @llvm.dbg.assign(metadata, metadata, metadata, metadata, metadata, metadata)
 declare void @llvm.memset.p0i8.i64(ptr nocapture writeonly, i8, i64, i1 immarg)
 
 !llvm.dbg.cu = !{!0}
 !llvm.module.flags = !{!3, !4, !5, !1000}
 !llvm.ident = !{!6}
 
 !0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 12.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, splitDebugInlining: false, nameTableKind: None)

llvm/test/DebugInfo/Generic/assignment-tracking/dse/shorten-offset.ll

+; RUN: opt %s -S -passes=dse -o - | FileCheck %s --implicit-check-not="call void @llvm.dbg"
+
+;; Based on the test shorten.ll with some adjustments.
+;;
+;; $ cat test.cpp
+;; void esc(char*);
+;; void shortenEnd() {
+;;   char local[80];                      //        bits    frag
+;;   __builtin_memset(local + 8,  0, 24); // local:  64-160 ( 64, 96)
+;;   __builtin_memset(local + 16, 8, 40); // local: 128-160 (128, 32)
+;;   esc(local);
+;; }
+;; void shortenStart() {
+;;   char local2[40];                 //          bits   frag
+;;   __builtin_memset(local2, 0, 40); // local2:  0-160  (0, 160)
+;;   __builtin_memset(local2, 8, 16); // local2:  0-128  (0, 128)
+;;   esc(local2);
+;; }
+
+;; The variables and intrinsics have been adjusted with by hand to test
+;; what happens when the variable doesn't fill the whole alloca, and
+;; when offsets are encoded with both the address component of the dbg.assign
+;; and the address modifying DIExpression.
+
+;; DeadStoreElimination will shorten the first store in shortenEnd from [64,
+;; 192) bits to [64, 128) bits. Variable 'local' has been adjusted to be 160
+;; bits large. Check that we get an unlinked dbg.assign covering the deleted
+;; bits that overlap the dbg.assign's fagment: [128, 160) (offset=128 size=32).
+
+; CHECK: @_Z10shortenEndv
+; CHECK:      call void @llvm.dbg.assign({{.*}}, metadata ptr %local, metadata !DIExpression())
+; CHECK:      call void @llvm.memset{{.*}}, !DIAssignID ![[ID:[0-9]+]]
+; CHECK-NEXT: call void @llvm.dbg.assign(metadata i8 0, metadata ![[VAR:[0-9]+]], metadata !DIExpression(DW_OP_LLVM_fragment, 64, 96), metadata ![[ID:[0-9]+]], metadata ptr %offset_4_bytes, metadata !DIExpression(DW_OP_plus_uconst, 4))
+; CHECK-NEXT: call void @llvm.dbg.assign(metadata i8 0, metadata ![[VAR]], metadata !DIExpression(DW_OP_LLVM_fragment, 128, 32), metadata ![[UniqueID1:[0-9]+]], metadata ptr undef, metadata !DIExpression({{.*}}))
+
+;; DSE will shorten the first store in shortenStart from [0, 160) bits to [128,
+;; 160) bits. Variable 'local2' has been adjusted to be 160 bits.  Check we get
+;; an unlinked dbg.assign covering the deleted bits that overlap the
+;; dbg.assign's fragment (no fragment in this case, i.e. the whole variable):
+;; [0, 128) (offset=0, size=128).
+
+; CHECK: @_Z12shortenStartv
+; CHECK:      call void @llvm.dbg.assign({{.*}}, metadata ptr %local2, metadata !DIExpression())
+; CHECK:      call void @llvm.memset{{.*}}, !DIAssignID ![[ID2:[0-9]+]]
+; CHECK-NEXT: call void @llvm.dbg.assign(metadata i8 0, metadata ![[VAR2:[0-9]+]], metadata !DIExpression(), metadata ![[ID2]], metadata ptr %local2, metadata !DIExpression())
+; CHECK-NEXT: call void @llvm.dbg.assign(metadata i8 0, metadata ![[VAR2]], metadata !DIExpression(DW_OP_LLVM_fragment, 0, 128), metadata ![[UniqueID2:[0-9]+]], metadata ptr undef, metadata !DIExpression())
+
+; CHECK-DAG: ![[ID]] = distinct !DIAssignID()
+; CHECK-DAG: ![[UniqueID1]] = distinct !DIAssignID()
+; CHECK-DAG: ![[UniqueID2]] = distinct !DIAssignID()
+
+define dso_local void @_Z10shortenEndv() local_unnamed_addr #0 !dbg !7 {
+entry:
+  %local = alloca [80 x i8], align 16, !DIAssignID !16
+  call void @llvm.dbg.assign(metadata i1 undef, metadata !11, metadata !DIExpression(), metadata !16, metadata ptr %local, metadata !DIExpression()), !dbg !17
+  %arraydecay = getelementptr inbounds [80 x i8], ptr %local, i64 0, i64 0, !dbg !19
+  %offset_4_bytes = getelementptr inbounds [80 x i8], ptr %local, i64 0, i64 4, !dbg !21
+  %offset_8_bytes = getelementptr inbounds [80 x i8], ptr %local, i64 0, i64 8, !dbg !21
+  call void @llvm.memset.p0i8.i64(ptr noundef nonnull align 16 dereferenceable(24) %offset_8_bytes, i8 0, i64 72, i1 false), !dbg !19, !DIAssignID !20
+  call void @llvm.dbg.assign(metadata i8 0, metadata !11, metadata !DIExpression(DW_OP_LLVM_fragment, 64, 96), metadata !20, metadata ptr %offset_4_bytes, metadata !DIExpression(DW_OP_plus_uconst, 4)), !dbg !17
+  %offset_16_bytes = getelementptr inbounds [80 x i8], ptr %local, i64 0, i64 4, !dbg !21
+  call void @llvm.memset.p0i8.i64(ptr noundef nonnull align 16 dereferenceable(40) %offset_16_bytes, i8 8, i64 64, i1 false), !dbg !22, !DIAssignID !23
+  call void @_Z3escPi(ptr noundef nonnull %arraydecay), !dbg !24
+  ret void, !dbg !25
+}
+
+declare void @llvm.memset.p0i8.i64(ptr nocapture writeonly, i8, i64, i1 immarg)
+declare !dbg !26 dso_local void @_Z3escPi(ptr noundef) local_unnamed_addr
+
+define dso_local void @_Z12shortenStartv() local_unnamed_addr #0 !dbg !31 {
+entry:
+  %local2 = alloca [40 x i8], align 16, !DIAssignID !37
+  call void @llvm.dbg.assign(metadata i1 undef, metadata !33, metadata !DIExpression(), metadata !37, metadata ptr %local2, metadata !DIExpression()), !dbg !38
+  %arraydecay = getelementptr inbounds [40 x i8], ptr %local2, i64 0, i64 0, !dbg !40
+  call void @llvm.memset.p0i8.i64(ptr noundef nonnull align 16 dereferenceable(40) %local2, i8 0, i64 36, i1 false), !dbg !40, !DIAssignID !41
+  call void @llvm.dbg.assign(metadata i8 0, metadata !33, metadata !DIExpression(), metadata !41, metadata ptr %local2, metadata !DIExpression()), !dbg !38
+  call void @llvm.memset.p0i8.i64(ptr noundef nonnull align 16 dereferenceable(16) %local2, i8 8, i64 16, i1 false), !dbg !42, !DIAssignID !43
+  call void @_Z3escPi(ptr noundef nonnull %arraydecay), !dbg !44
+  ret void, !dbg !45
+}
+
+declare void @llvm.dbg.assign(metadata, metadata, metadata, metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2, !3, !4, !5, !1000}
+!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: "shortenEnd", linkageName: "_Z10shortenEndv", scope: !1, file: !1, line: 2, type: !8, scopeLine: 2, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !10)
+!8 = !DISubroutineType(types: !9)
+!9 = !{null}
+!10 = !{!11}
+!11 = !DILocalVariable(name: "local", scope: !7, file: !1, line: 3, type: !12)
+!12 = !DICompositeType(tag: DW_TAG_array_type, baseType: !13, size: 160, elements: !14)
+!13 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!14 = !{!15}
+!15 = !DISubrange(count: 5)
+!16 = distinct !DIAssignID()
+!17 = !DILocation(line: 0, scope: !7)
+!18 = !DILocation(line: 3, column: 3, scope: !7)
+!19 = !DILocation(line: 4, column: 3, scope: !7)
+!20 = distinct !DIAssignID()
+!21 = !DILocation(line: 5, column: 26, scope: !7)
+!22 = !DILocation(line: 5, column: 3, scope: !7)
+!23 = distinct !DIAssignID()
+!24 = !DILocation(line: 6, column: 3, scope: !7)
+!25 = !DILocation(line: 7, column: 1, scope: !7)
+!26 = !DISubprogram(name: "esc", linkageName: "_Z3escPi", scope: !1, file: !1, line: 1, type: !27, flags: DIFlagPrototyped, spFlags: DISPFlagOptimized, retainedNodes: !30)
+!27 = !DISubroutineType(types: !28)
+!28 = !{null, !29}
+!29 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !13, size: 64)
+!30 = !{}
+!31 = distinct !DISubprogram(name: "shortenStart", linkageName: "_Z12shortenStartv", scope: !1, file: !1, line: 8, type: !8, scopeLine: 8, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !32)
+!32 = !{!33}
+!33 = !DILocalVariable(name: "local2", scope: !31, file: !1, line: 9, type: !34)
+!34 = !DICompositeType(tag: DW_TAG_array_type, baseType: !13, size: 160, elements: !35)
+!35 = !{!36}
+!36 = !DISubrange(count: 5)
+!37 = distinct !DIAssignID()
+!38 = !DILocation(line: 0, scope: !31)
+!39 = !DILocation(line: 9, column: 3, scope: !31)
+!40 = !DILocation(line: 10, column: 3, scope: !31)
+!41 = distinct !DIAssignID()
+!42 = !DILocation(line: 11, column: 3, scope: !31)
+!43 = distinct !DIAssignID()
+!44 = !DILocation(line: 12, column: 3, scope: !31)
+!45 = !DILocation(line: 13, column: 1, scope: !31)
+!1000 = !{i32 7, !"debug-info-assignment-tracking", i1 true}

llvm/test/DebugInfo/Generic/assignment-tracking/dse/shorten.ll

 ; CHECK-DAG: ![[ID]] = distinct !DIAssignID()
 ; CHECK-DAG: ![[UniqueID1]] = distinct !DIAssignID()
 ; CHECK-DAG: ![[UniqueID2]] = distinct !DIAssignID()
 
 define dso_local void @_Z10shortenEndv() local_unnamed_addr #0 !dbg !7 {
 entry:
   %local = alloca [20 x i32], align 16, !DIAssignID !16
   call void @llvm.dbg.assign(metadata i1 undef, metadata !11, metadata !DIExpression(), metadata !16, metadata ptr %local, metadata !DIExpression()), !dbg !17
-  call void @llvm.lifetime.start.p0i8(i64 80, ptr nonnull %local) #5, !dbg !18
   %arraydecay = getelementptr inbounds [20 x i32], ptr %local, i64 0, i64 0, !dbg !19
   call void @llvm.memset.p0i8.i64(ptr noundef nonnull align 16 dereferenceable(24) %local, i8 0, i64 24, i1 false), !dbg !19, !DIAssignID !20
   call void @llvm.dbg.assign(metadata i8 0, metadata !11, metadata !DIExpression(DW_OP_LLVM_fragment, 0, 192), metadata !20, metadata ptr %local, metadata !DIExpression()), !dbg !17
   %add.ptr = getelementptr inbounds [20 x i32], ptr %local, i64 0, i64 4, !dbg !21
   call void @llvm.memset.p0i8.i64(ptr noundef nonnull align 16 dereferenceable(40) %add.ptr, i8 8, i64 40, i1 false), !dbg !22, !DIAssignID !23
   call void @llvm.dbg.assign(metadata i1 undef, metadata !11, metadata !DIExpression(DW_OP_LLVM_fragment, 128, 320), metadata !23, metadata ptr %add.ptr, metadata !DIExpression()), !dbg !17
   call void @_Z3escPi(ptr noundef nonnull %arraydecay), !dbg !24
-  call void @llvm.lifetime.end.p0i8(i64 80, ptr nonnull %local) #5, !dbg !25
   ret void, !dbg !25
 }
 
-declare void @llvm.lifetime.start.p0i8(i64 immarg, ptr nocapture)
 declare void @llvm.memset.p0i8.i64(ptr nocapture writeonly, i8, i64, i1 immarg)
 declare !dbg !26 dso_local void @_Z3escPi(ptr noundef) local_unnamed_addr
-declare void @llvm.lifetime.end.p0i8(i64 immarg, ptr nocapture)
 
 define dso_local void @_Z12shortenStartv() local_unnamed_addr #0 !dbg !31 {
 entry:
   %local2 = alloca [10 x i32], align 16, !DIAssignID !37
   call void @llvm.dbg.assign(metadata i1 undef, metadata !33, metadata !DIExpression(), metadata !37, metadata ptr %local2, metadata !DIExpression()), !dbg !38
-  call void @llvm.lifetime.start.p0i8(i64 40, ptr nonnull %local2) #5, !dbg !39
   %arraydecay = getelementptr inbounds [10 x i32], ptr %local2, i64 0, i64 0, !dbg !40
   call void @llvm.memset.p0i8.i64(ptr noundef nonnull align 16 dereferenceable(40) %local2, i8 0, i64 40, i1 false), !dbg !40, !DIAssignID !41
   call void @llvm.dbg.assign(metadata i8 0, metadata !33, metadata !DIExpression(), metadata !41, metadata ptr %local2, metadata !DIExpression()), !dbg !38
   call void @llvm.memset.p0i8.i64(ptr noundef nonnull align 16 dereferenceable(16) %local2, i8 8, i64 16, i1 false), !dbg !42, !DIAssignID !43
   call void @llvm.dbg.assign(metadata i1 undef, metadata !33, metadata !DIExpression(DW_OP_LLVM_fragment, 0, 128), metadata !43, metadata ptr %local2, metadata !DIExpression()), !dbg !38
   call void @_Z3escPi(ptr noundef nonnull %arraydecay), !dbg !44
-  call void @llvm.lifetime.end.p0i8(i64 40, ptr nonnull %local2) #5, !dbg !45
   ret void, !dbg !45
 }
 
 declare void @llvm.dbg.assign(metadata, metadata, metadata, metadata, metadata, metadata)
 
 !llvm.dbg.cu = !{!0}
 !llvm.module.flags = !{!2, !3, !4, !5, !1000}
 !llvm.ident = !{!6}