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XLS Tools

An index of XLS developer tools.


Constructs a binary decision diagram (BDD) using a given XLS function and prints various statistics about the BDD. BDD construction can be very slow in pathological cases and this utility is useful for identifying the underlying causes. Accepts arbitrary IR as input or a benchmark specified by name.


Prints numerous metrics and other information about an XLS IR file including: total delay, critical path, codegen information, optimization time, etc. This tool may be run against arbitrary IR not just the fixed set of XLS benchmarks. The output of this tool is scraped by run_benchmarks to construct a table comparing metrics against a mint CL across the benchmark suite.


Rewrites an XLS IR function in terms of its ops' fundamental AND/OR/NOT constituents, i.e., makes all operations boolean, thus it's "booleanifying" the function.


Lowers an XLS IR file into Verilog. Options include emitting a feedforward pipeline or a purely combinational block. Emits both a Verilog file and a module signature which includes metadata about the block. The tool does not run any XLS passes so unoptimized IR may fail if the IR contains constructs not expected by the backend.

For a detailed list of codegen options including I/O configurations, please visit the codegen options page.


Dumps delay information about an XLS function including per-node delay information and critical-path.


Evaluates an XLS IR file with user-specified or random inputs. Includes features for evaluating the IR before and after optimizations which makes this tool very useful for identifying optimization bugs.

This tool accepts two [mutually exclusive] optional args, --input_validator_expr and --input_validator_path, which allow the user to specify an expression to "filter" potential input values to discard invalid ones. For both, the filter must be a function, named validator, and must take params of the same layout as the function under test. This function should return true if the inputs are valid for the function and false otherwise. --input_validator_expr lists the function as an inline command-line argument, whereas --input_validator_path holds the path to a .x file containing the validation function.


Tool for reducing IR to a minimal test case based on an external test.


Prints summary information/stats on an IR [Package] file. An example:

$ bazel-bin/xls/tools/ir_stats_main bazel-genfiles/xls/modules/
Package "fp32_add_2"
  Function: "__float32__is_inf"
    Signature: ((bits[1], bits[8], bits[23])) -> bits[1]
    Nodes: 8

  Function: "__float32__is_nan"
    Signature: ((bits[1], bits[8], bits[23])) -> bits[1]
    Nodes: 8

  Function: "__fp32_add_2__fp32_add_2"
    Signature: ((bits[1], bits[8], bits[23]), (bits[1], bits[8], bits[23])) -> (bits[1], bits[8], bits[23])
    Nodes: 252


Verifies that two IR files (for example, optimized and unoptimized IR from the same source) are logically equivalent.


Runs XLS IR through the optimization pipeline.


Takes in a proto schema and a textproto instance thereof and outputs a DSLX module containing a DSLX type and constant matching both inputs, respectively.

Not all protocol buffer types map to DSLX types, so there are some restrictions or other behaviors requiring explanation:

  1. Only scalar and repeated fields are supported (i.e., no maps or oneofs, etc.).
  2. Only recursively-integral messages are supported, that is to say, a message may contain submessages, as long as all non-Message fields are integral.
  3. Since DSLX doesn't support variable arrays and Protocol Buffers don't support fixed-length repeated fields. To unify this, all instances of repeated-field-containing Messages must have the same size of their repeated members (declared as arrays in DSLX). This size will be calculated as the maximum size of any instance of that repeated field across all instances in the input textproto. For example, if a message Foo has a repeated field bar, and this message is present multiple times in the input textproto, say as:
      foo: {
        bar: 1
      foo: {
        bar: 1
        bar: 2
      foo: {
        bar: 1
        bar: 2
        bar: 3

    the DSLX version of Foo will declare bar has a 3-element array. An accessory field, bar_count, will also be created, which will contain the number of valid entries in an actual instance of Foo::bar.

    The "Fields" example in ./xls/tools/testdata/proto_to_dslx_main.* demonstrates this behavior.


Allows you to interactively run various parts of the compiler, including parsing/type checking (:reload), lowering/optimization (:ir), Verilog codegen (:verilog [identifier]), and LLVM codegen (:llvm, not yet implemented). You can also inspect the IR types of identifiers with :type, and even imported identifiers can be accessed with :type foo::bar.

animated GIF


Runs a Verilog block emitted by XLS through a Verilog simulator. Requires both the Verilog text and the module signature which includes metadata about the block.


Simple driver for Z3IrTranslator - converts a given IR function into its Z3 representation and outputs that translation as SMTLIB2.

First obtain an XLS IR file:

$ bazel build -c opt //xls/

And then feed that XLS IR file into this binary:

$ bazel run -c opt //xls/tools:smtlib_emitter_main -- --ir_path \
(bvadd (concat #b0 x) (concat #b0 y))

To turn it into "gate level" SMTLib, we can do a pre-pass through the booleanify_main tool:

$ bazel run -c opt //xls/tools:booleanify_main -- --ir_path \
   $PWD/bazel-bin/xls/examples/ \
   > /tmp/
$ bazel run -c opt //xls/tools:smtlib_emitter_main -- \
    --ir_path /tmp/
(let ((a!1 (bvand (bvor ((_ extract 0 0) x) ((_ extract 0 0) y))
                  (bvnot (bvand ((_ extract 0 0) x) ((_ extract 0 0) y))))))
(let ((a!2 (bvor (bvand (bvor #b0 #b0) (bvnot (bvand #b0 #b0)))
                 (bvor (bvand ((_ extract 0 0) x) ((_ extract 0 0) y))
                       (bvand a!1 #b0))))
      (a!3 (bvand (bvand (bvor #b0 #b0) (bvnot (bvand #b0 #b0)))
                  (bvor (bvand ((_ extract 0 0) x) ((_ extract 0 0) y))
                        (bvand a!1 #b0)))))
  (concat (bvand a!2 (bvnot a!3))
          (bvand (bvor a!1 #b0) (bvnot (bvand a!1 #b0))))))


Uses a SMT solver (i.e. Z3) to prove properties of an XLS IR program from the command line. Currently the set of "predicates" that the solver supports from the command line are limited, but in theory it is capable of solving for arbitrary IR-function-specified predicates.

This can be used to uncover opportunities for optimization that were missed, or to prove equivalence of transformed representations with their original version.


Parses a cell library ".lib" file and extracts boolean formulas from it that determine the functionality of cells. This is useful for LEC of the XLS IR against the post-synthesis netlist.


Performs terminal-based color code highlighting of a DSL file.


Dumps type information that has been deduced for a given DSL file.

Development Tools


For C++ development, you might need a compilation database to have good support in your IDE. You can create the compile_commands.json by running this script.


To run clang-tidy and create a report of things that might be worthwhile fixing, use the following script:


(Note, this will be pretty slow on the first run, but it caches results and will only reprocess changed files in subsequent runs).

The output of the clang-tidy runs shows up in the xls_clang-tidy.out file which is formatted just like an output from a compiler. So to quickly work with these, you can use cat xls_clang-tidy.out as your 'compiler invocation' in your IDE (e.g. M-x compile in emacs) and step through next-error locations as usual.

Golden Comparison Files

To re-generate golden reference files (for all test targets that use golden reference file comparisons), run: