[llvm] Fix non-determinism in debuginfo (PR #68332)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-ir

<details>
<summary>Changes</summary>

Assignment tracking iterates over a SmallSet when adding metadata, which eventually results in debug metadata being added to the module in non-deterministic order.

As reported in #<!-- -->63921, we saw some cases where DWARF DebugLoc entries could have their order reversed, even though there was no functional difference.

This patch replaces the `SmallSet` with a `SmallVector`, and adds the required `DenseMapInfo` specialization to make the ordering deterministic.

Fixes #<!-- -->63921

---
Full diff: https://github.com/llvm/llvm-project/pull/68332.diff


1 Files Affected:

- (modified) llvm/include/llvm/IR/DebugInfo.h (+23-1) 


``````````diff
diff --git a/llvm/include/llvm/IR/DebugInfo.h b/llvm/include/llvm/IR/DebugInfo.h
index 26a7cfbbb350234..c5ded71406d885e 100644
--- a/llvm/include/llvm/IR/DebugInfo.h
+++ b/llvm/include/llvm/IR/DebugInfo.h
@@ -16,7 +16,9 @@
 #ifndef LLVM_IR_DEBUGINFO_H
 #define LLVM_IR_DEBUGINFO_H
 
+#include "llvm/ADT/DenseMapInfo.h"
 #include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SetVector.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/SmallSet.h"
 #include "llvm/ADT/SmallVector.h"
@@ -263,7 +265,8 @@ struct VarRecord {
 /// TODO: Backing storage shouldn't be limited to allocas only. Some local
 /// variables have their storage allocated by the calling function (addresses
 /// passed in with sret & byval parameters).
-using StorageToVarsMap = DenseMap<const AllocaInst *, SmallSet<VarRecord, 2>>;
+using StorageToVarsMap =
+    DenseMap<const AllocaInst *, SmallSetVector<VarRecord, 2>>;
 
 /// Track assignments to \p Vars between \p Start and \p End.
 
@@ -314,6 +317,25 @@ class AssignmentTrackingPass : public PassInfoMixin<AssignmentTrackingPass> {
 
 /// Return true if assignment tracking is enabled for module \p M.
 bool isAssignmentTrackingEnabled(const Module &M);
+
+template <> struct DenseMapInfo<at::VarRecord> {
+  static inline at::VarRecord getEmptyKey() {
+    return at::VarRecord{nullptr, nullptr};
+  }
+
+  static inline at::VarRecord getTombstoneKey() {
+    return at::VarRecord{nullptr, nullptr};
+  }
+
+  static unsigned getHashValue(const at::VarRecord &Var) {
+    return hash_combine(Var.Var, Var.DL);
+  }
+
+  static bool isEqual(const at::VarRecord &A, const at::VarRecord &B) {
+    return A == B;
+  }
+};
+
 } // end namespace llvm
 
 #endif // LLVM_IR_DEBUGINFO_H

``````````

</details>


https://github.com/llvm/llvm-project/pull/68332