[mlir][Linalg] Fix warnings/errors on D155518.

[mravishankar]

Summary

This fixes some warnings (that were caught as errors) in https://reviews.llvm.org/D155518/.

mlir/lib/Dialect/Linalg/Transforms/DropUnitDims.cpp

auto isUnitDim = [&](unsigned dim) {
     // constant 0.
     if (operandShape[dim] == 1) {
       auto constAffineExpr = exprs[dim].dyn_cast<AffineConstantExpr>();
       return constAffineExpr && constAffineExpr.getValue() == 0;
     }
     return false;
   };
 
-  int64_t dim = 0;
+  unsigned dim = 0;
   while (dim < operandShape.size() && isUnitDim(dim))
     reassociationGroup.push_back(dim++);
   while (dim < operandShape.size()) {
     assert(!isUnitDim(dim) && "expected non unit-extent");
     reassociationGroup.push_back(dim);
     AffineExpr newExpr = exprs[dim].replaceDims(dimReplacements);
     newIndexExprs.push_back(newExpr);
     info.targetShape.push_back(operandShape[dim]);
LogicalResult linalg::dropUnitDims(RewriterBase &rewriter, GenericOp genericOp,
   SmallVector<unsigned> allowedUnitDims = options.controlFn(genericOp);
   if (allowedUnitDims.empty()) {
     return rewriter.notifyMatchFailure(
         genericOp, "control function returns no allowed unit dims to prune");
   }
   llvm::SmallDenseSet<unsigned> unitDimsFilter(allowedUnitDims.begin(),
                                                allowedUnitDims.end());
   llvm::SmallDenseSet<unsigned> unitDims;
-  ArrayAttr iteratorTypes = genericOp.getIteratorTypes();
   for (const auto &expr : enumerate(invertedMap.getResults())) {
     if (AffineDimExpr dimExpr = expr.value().dyn_cast<AffineDimExpr>()) {
       if (dims[dimExpr.getPosition()] == 1 &&
           unitDimsFilter.count(expr.index()))
         unitDims.insert(expr.index());
     }
   }
 

mlir/test/lib/Dialect/Linalg/TestLinalgDropUnitDims.cpp

void runOnOperation() override {
     func::FuncOp funcOp = this->getOperation();
     IRRewriter rewriter(context);
     SmallVector<linalg::GenericOp> genericOps;
     funcOp.walk(
         [&](linalg::GenericOp genericOp) { genericOps.push_back(genericOp); });
 
     for (auto genericOp : genericOps) {
       rewriter.setInsertionPoint(genericOp);
-      dropOutermostUnitDims(rewriter, genericOp);
+      (void)dropOutermostUnitDims(rewriter, genericOp);
     }
   }
 };
 } // namespace
 
 namespace mlir {
 namespace test {
 void registerTestLinalgDropUnitDims() {
   PassRegistration<TestLinalgDropUnitDims>();
 }
 } // namespace test
 } // namespace mlir