[LiveDebugVariables] Add basic verification

[jayfoad]

Add a basic implementation of verifyAnalysis that just checks that the
analysis does not refer to any SlotIndexes for instructions that have
been deleted. This was useful for diagnosing some SlotIndexes-related
problems caused by #67038.

[llvmbot]

@llvm/pr-subscribers-debuginfo

@llvm/pr-subscribers-llvm-regalloc

Author: Jay Foad (jayfoad)

Changes

Add a basic implementation of verifyAnalysis that just checks that the
analysis does not refer to any SlotIndexes for instructions that have
been deleted. This was useful for diagnosing some SlotIndexes-related
problems caused by #67038.- [SlotIndexes] Implement support for poison checks

---

Full diff: https://github.com/llvm/llvm-project/pull/79846.diff

4 Files Affected:

• (modified) llvm/include/llvm/CodeGen/SlotIndexes.h (+27-4)
• (modified) llvm/lib/CodeGen/LiveDebugVariables.cpp (+17)
• (modified) llvm/lib/CodeGen/LiveDebugVariables.h (+1)
• (modified) llvm/lib/CodeGen/SlotIndexes.cpp (+2)

diff --git a/llvm/include/llvm/CodeGen/SlotIndexes.h b/llvm/include/llvm/CodeGen/SlotIndexes.h
index 72f4a6876b6cb14..2b437a0649aac22 100644
--- a/llvm/include/llvm/CodeGen/SlotIndexes.h
+++ b/llvm/include/llvm/CodeGen/SlotIndexes.h
@@ -43,21 +43,40 @@ class raw_ostream;
   /// SlotIndex & SlotIndexes classes for the public interface to this
   /// information.
   class IndexListEntry : public ilist_node<IndexListEntry> {
-    MachineInstr *mi;
+#if NDEBUG
+    // Disable poison checks such that setPoison will do nothing and isPoisoned
+    // will return false.
+    static constexpr unsigned PoisonBits = 0;
+    static constexpr unsigned PoisonVal = 0;
+#else
+    static constexpr unsigned PoisonBits = 1;
+    static constexpr unsigned PoisonVal = 1;
+#endif
+
+    PointerIntPair<MachineInstr *, PoisonBits, unsigned> mi;
     unsigned index;
 
   public:
-    IndexListEntry(MachineInstr *mi, unsigned index) : mi(mi), index(index) {}
+    IndexListEntry(MachineInstr *mi, unsigned index) : mi(mi, 0), index(index) {
+    }
 
-    MachineInstr* getInstr() const { return mi; }
+    MachineInstr* getInstr() const { return mi.getPointer(); }
     void setInstr(MachineInstr *mi) {
-      this->mi = mi;
+      this->mi.setPointer(mi);
     }
 
     unsigned getIndex() const { return index; }
     void setIndex(unsigned index) {
       this->index = index;
     }
+
+    void setPoison() {
+      mi.setInt(PoisonVal);
+    }
+
+    bool isPoisoned() const {
+      return mi.getInt();
+    }
   };
 
   template <>
@@ -285,6 +304,10 @@ class raw_ostream;
     SlotIndex getPrevIndex() const {
       return SlotIndex(&*--listEntry()->getIterator(), getSlot());
     }
+
+    bool isPoisoned() const {
+      return listEntry()->isPoisoned();
+    }
   };
 
   inline raw_ostream& operator<<(raw_ostream &os, SlotIndex li) {
diff --git a/llvm/lib/CodeGen/LiveDebugVariables.cpp b/llvm/lib/CodeGen/LiveDebugVariables.cpp
index 7cb90af5ff173ed..93b9566b21370ad 100644
--- a/llvm/lib/CodeGen/LiveDebugVariables.cpp
+++ b/llvm/lib/CodeGen/LiveDebugVariables.cpp
@@ -492,6 +492,13 @@ class UserValue {
   /// Return DebugLoc of this UserValue.
   const DebugLoc &getDebugLoc() { return dl; }
 
+  void verify() const {
+    for (auto I = locInts.begin(), E = locInts.end(); I != E; ++I) {
+      assert(!I.start().isPoisoned());
+      assert(!I.stop().isPoisoned());
+    }
+  }
+
   void print(raw_ostream &, const TargetRegisterInfo *);
 };
 
@@ -655,6 +662,11 @@ class LDVImpl {
     ModifiedMF = false;
   }
 
+  void verify() const {
+    for (auto [DV, UV] : userVarMap)
+      UV->verify();
+  }
+
   /// Map virtual register to an equivalence class.
   void mapVirtReg(Register VirtReg, UserValue *EC);
 
@@ -1320,6 +1332,11 @@ void LiveDebugVariables::releaseMemory() {
     static_cast<LDVImpl*>(pImpl)->clear();
 }
 
+void LiveDebugVariables::verifyAnalysis() const {
+  if (pImpl)
+    static_cast<LDVImpl *>(pImpl)->verify();
+}
+
 LiveDebugVariables::~LiveDebugVariables() {
   if (pImpl)
     delete static_cast<LDVImpl*>(pImpl);
diff --git a/llvm/lib/CodeGen/LiveDebugVariables.h b/llvm/lib/CodeGen/LiveDebugVariables.h
index 9998ce9e8dad861..c99f11c8565a819 100644
--- a/llvm/lib/CodeGen/LiveDebugVariables.h
+++ b/llvm/lib/CodeGen/LiveDebugVariables.h
@@ -56,6 +56,7 @@ class LLVM_LIBRARY_VISIBILITY LiveDebugVariables : public MachineFunctionPass {
   bool runOnMachineFunction(MachineFunction &) override;
   void releaseMemory() override;
   void getAnalysisUsage(AnalysisUsage &) const override;
+  void verifyAnalysis() const override;
 
   MachineFunctionProperties getSetProperties() const override {
     return MachineFunctionProperties().set(
diff --git a/llvm/lib/CodeGen/SlotIndexes.cpp b/llvm/lib/CodeGen/SlotIndexes.cpp
index 8b80c6ccb438936..762aab2ec2557e3 100644
--- a/llvm/lib/CodeGen/SlotIndexes.cpp
+++ b/llvm/lib/CodeGen/SlotIndexes.cpp
@@ -126,6 +126,7 @@ void SlotIndexes::removeMachineInstrFromMaps(MachineInstr &MI,
   mi2iMap.erase(mi2iItr);
   // FIXME: Eventually we want to actually delete these indexes.
   MIEntry.setInstr(nullptr);
+  MIEntry.setPoison();
 }
 
 void SlotIndexes::removeSingleMachineInstrFromMaps(MachineInstr &MI) {
@@ -152,6 +153,7 @@ void SlotIndexes::removeSingleMachineInstrFromMaps(MachineInstr &MI) {
   } else {
     // FIXME: Eventually we want to actually delete these indexes.
     MIEntry.setInstr(nullptr);
+    MIEntry.setPoison();
   }
 }
 

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[adrian-prantl]

Suggested change

	for (auto I = locInts.begin(), E = locInts.end(); I != E; ++I) {
	for (auto I : locInts) {

[jayfoad]

I don't think this works because I need to call start and stop which are methods on the iterator itself (an instance of IntervalMap::const_iterator).

[SLTozer]

Adding the verification SGTM - LiveDebugVariables can be a moderately hot pass (though LiveDebugValues is the real killer) and PointerIntPair can cause a bit of a slowdown compared to just pointer operations, but I expect this won't have a noticeable impact.

[jayfoad]

Adding the verification SGTM - LiveDebugVariables can be a moderately hot pass (though LiveDebugValues is the real killer) and PointerIntPair can cause a bit of a slowdown compared to just pointer operations, but I expect this won't have a noticeable impact.

I should have mentioned that I cannot commit this patch as-is because it causes lit test failures. I think these are all pre-existing problems with LiveDebugVariables that would need to be fixed. There was some prior discussion about this in the previous iteration of this review, #68703. I'd appreciate any help with understanding or fixing the failures!

Failed Tests (6):
  LLVM :: CodeGen/Thumb2/pr52817.ll
  LLVM :: DebugInfo/ARM/PR26163.ll
  LLVM :: DebugInfo/COFF/fpo-csrs.ll
  LLVM :: DebugInfo/X86/pr34545.ll
  LLVM :: DebugInfo/X86/spill-indirect-nrvo.ll
  LLVM :: tools/llvm-dwarfdump/X86/LTO_CCU_zero_loc_cov.ll