[MLIR] Fix areIdsUnique in AffineStructures

[Groverkss]

Summary

This patch fixes a bug in areIdsUnique where it ignores the [start, end] range.

No test case is added since there are no use cases through IR from where it
can be tested, and it is hard to create a unittest since we do not currently
have Values in unittests.

[arjunp]

LGTM, maybe mention that it's hard to add a test case because of it being static and not being able to use Values in unittests (AFAIK)

[grosser]

Indeed. If no test case is provided, there should be an explanation in the commit message why providing a test case is impractical.

mlir/lib/Dialect/Affine/Analysis/AffineStructures.cpp

static bool LLVM_ATTRIBUTE_UNUSED areIdsUnique(
 
   assert(start <= cst.getNumIds() && "Start position out of bounds");
   assert(end <= cst.getNumIds() && "End position out of bounds");
 
   if (start >= end)
     return true;
 
   SmallPtrSet<Value, 8> uniqueIds;
-  ArrayRef<Optional<Value>> maybeValues = cst.getMaybeValues();
+  ArrayRef<Optional<Value>> maybeValues =
+      cst.getMaybeValues().slice(start, end - start);
   for (Optional<Value> val : maybeValues) {
     if (val.hasValue() && !uniqueIds.insert(val.getValue()).second)
       return false;
   }
   return true;
 }
 
 /// Checks if the SSA values associated with `cst`'s identifiers are unique.