[Mlir-commits] [mlir] [MLIR][Presburger] Implement IntegerRelation::mergeAndAlignSymbols (PR #76736)

[Kunwar Grover]

================
@@ -1288,6 +1288,37 @@ void IntegerRelation::eliminateRedundantLocalVar(unsigned posA, unsigned posB) {
   removeVar(posB);
 }
 
+void IntegerRelation::mergeAndAlignSymbols(IntegerRelation &other) {
+  assert(space.isUsingIds() && other.space.isUsingIds() &&
+         "Both relations need to have identifers to merge & align");
+
+  // First merge & align identifiers into `other` from `this`.
+  unsigned i = 0;
+  for (const Identifier identifier : space.getIds(VarKind::Symbol)) {
+    // If the identifier exists in `other`, then align it; otherwise insert it
+    // assuming it is a new identifier. Search in `other` starting at position
+    // `i` since the left of `i` is aligned.
+    auto *findBegin = other.space.getIds(VarKind::Symbol).begin() + i;
+    auto *findEnd = other.space.getIds(VarKind::Symbol).end();
+    auto *itr = std::find(findBegin, findEnd, identifier);
+    if (itr != findEnd) {
+      other.swapVar(other.getVarKindOffset(VarKind::Symbol) + i,
+                    other.getVarKindOffset(VarKind::Symbol) + i +
+                        std::distance(findBegin, itr));
+    } else {
+      other.insertVar(VarKind::Symbol, i);
+      other.space.getId(VarKind::Symbol, i) = identifier;
+    }
+    ++i;
+  }
+
+  // Finally add identifiers that are in `other`, but not in `this` to `this`.
+  for (unsigned e = other.getNumVarKind(VarKind::Symbol); i < e; ++i) {
+    insertVar(VarKind::Symbol, i);
----------------
Groverkss wrote:

We should add a insertVar variant with Identifier at some point. Not in this patch, but just wanted to point it out.

https://github.com/llvm/llvm-project/pull/76736