[mlir][arith] Expose dedicated API for expanding ceil/floor division

[antiagainst]

Summary

This allows more precise control over which patterns to pick to
expand arithmetic ops. Previously ceil/floor division epxansion
is only available together with various min/max op expansion.

[antiagainst]

Fix comments

mlir/include/mlir/Dialect/Arith/Transforms/Passes.h

 std::unique_ptr<Pass> createConstantBufferizePass(uint64_t alignment = 0);
 
 /// Adds patterns to emulate wide Arith and Function ops over integer
 /// types into supported ones. This is done by splitting original power-of-two
 /// i2N integer types into two iN halves.
 void populateWideIntEmulationPatterns(WideIntEmulationConverter &typeConverter,
                                       RewritePatternSet &patterns);
 
-/// Add patterns to expand Arith ops for LLVM lowering.
+/// Add patterns to expand Arith ceil/floor division ops.
+void populateCeilFloorDivExpandOpsPatterns(RewritePatternSet &patterns);
+
+/// Add patterns to expand Arith ops.
 void populateArithExpandOpsPatterns(RewritePatternSet &patterns);
 
-/// Create a pass to legalize Arith ops for LLVM lowering.
+/// Create a pass to legalize Arith ops.
 std::unique_ptr<Pass> createArithExpandOpsPass();
 
 /// Create a pass to replace signed ops with unsigned ones where they are proven
 /// equivalent.
 std::unique_ptr<Pass> createArithUnsignedWhenEquivalentPass();
 
 //===----------------------------------------------------------------------===//
 // Registration

mlir/lib/Dialect/Arith/Transforms/ExpandOps.cpp

void runOnOperation() override {
     if (failed(applyPartialConversion(getOperation(), target,
                                       std::move(patterns))))
       signalPassFailure();
   }
 };
 
 } // namespace
 
+void mlir::arith::populateCeilFloorDivExpandOpsPatterns(
+    RewritePatternSet &patterns) {
+  patterns
+      .add<CeilDivSIOpConverter, CeilDivUIOpConverter, FloorDivSIOpConverter>(
+          patterns.getContext());
+}
+
 void mlir::arith::populateArithExpandOpsPatterns(RewritePatternSet &patterns) {
+  populateCeilFloorDivExpandOpsPatterns(patterns);
   // clang-format off
   patterns.add<
-    CeilDivSIOpConverter,
-    CeilDivUIOpConverter,
-    FloorDivSIOpConverter,
     MaxMinFOpConverter<MaxFOp, arith::CmpFPredicate::UGT>,
     MaxMinFOpConverter<MinFOp, arith::CmpFPredicate::ULT>,
     MaxMinIOpConverter<MaxSIOp, arith::CmpIPredicate::sgt>,
     MaxMinIOpConverter<MaxUIOp, arith::CmpIPredicate::ugt>,
     MaxMinIOpConverter<MinSIOp, arith::CmpIPredicate::slt>,
     MaxMinIOpConverter<MinUIOp, arith::CmpIPredicate::ult>
    >(patterns.getContext());
   // clang-format on
 }
 
 std::unique_ptr<Pass> mlir::arith::createArithExpandOpsPass() {
   return std::make_unique<ArithExpandOpsPass>();
 }