[Mlir-commits] [mlir] [mlir][presburger] Preserve relative ordering of symbols and non-symbol vars when setting up SymbolicLexSimplex (PR #119036)

[Arjun P]

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@@ -229,25 +229,17 @@ PresburgerRelation IntegerRelation::computeReprWithOnlyDivLocals() const {
   // SymbolicLexOpt requires these to form a contiguous range.
   //
   // Take a copy so we can perform mutations.
-  IntegerRelation copy = *this;
   std::vector<MaybeLocalRepr> reprs(getNumLocalVars());
-  copy.getLocalReprs(&reprs);
+  this->getLocalReprs(&reprs);
 
-  // Iterate through all the locals. The last `numNonDivLocals` are the locals
-  // that have been scanned already and do not have division representations.
   unsigned numNonDivLocals = 0;
-  unsigned offset = copy.getVarKindOffset(VarKind::Local);
-  for (unsigned i = 0, e = copy.getNumLocalVars(); i < e - numNonDivLocals;) {
-    if (!reprs[i]) {
-      // Whenever we come across a local that does not have a division
-      // representation, we swap it to the `numNonDivLocals`-th last position
-      // and increment `numNonDivLocal`s. `reprs` also needs to be swapped.
-      copy.swapVar(offset + i, offset + e - numNonDivLocals - 1);
-      std::swap(reprs[i], reprs[e - numNonDivLocals - 1]);
-      ++numNonDivLocals;
+  llvm::SmallBitVector isSymbol(getNumVars(), true);
+  unsigned offset = getVarKindOffset(VarKind::Local);
+  for (unsigned i = 0, e = getNumLocalVars(); i < e; ++i) {
+    if (reprs[i])
       continue;
-    }
-    ++i;
+    isSymbol[offset + i] = false;
+    ++numNonDivLocals;
----------------
Superty wrote:

You can drop this variable `numNonDivLocals` and just use `isSymbol.count()` and `isSymbol.empty()`. I prefer simplifying the loop by doing this since these calls aren't going to impact performance

`isSymbol[offset + i] = bool(reprs[i])`

(Ideally I would add a function `hasRepr` to MaybeLocalRepr that does the same as the `bool()` but I'm happy to leave that for later.)

https://github.com/llvm/llvm-project/pull/119036