6c903f05f3
In the RISC-V architecture, multiple vendor-specific Control and Status Registers (CSRs) share the same encoding. However, the existing lookup function, which currently returns only a single result, falls short. During disassembly, it consistently returns the first CSR encountered, which may not be the correct CSR for the subtarget. To address this issue, we modify the function definition to return a range of results. These results can then be iterated upon to identify the CSR that best fits the subtarget’s feature requirements. The behavior of this new definition is controlled by a variable named `ReturnRange`, which defaults to `false`. Specifically, this patch introduces support for emitting a new lookup function for the primary key. This function returns a pair of iterators pointing to the first and last values, providing a comprehensive range of values that satisfy the query
LLVM TableGen
The purpose of TableGen is to generate complex output files based on information from source files that are significantly easier to code than the output files would be, and also easier to maintain and modify over time.
The information is coded in a declarative style involving classes and records, which are then processed by TableGen.
class Hello <string _msg> {
string msg = !strconcat("Hello ", _msg);
}
def HelloWorld: Hello<"world!"> {}
------------- Classes -----------------
class Hello<string Hello:_msg = ?> {
string msg = !strconcat("Hello ", Hello:_msg);
}
------------- Defs -----------------
def HelloWorld { // Hello
string msg = "Hello world!";
}
Try this example on Compiler Explorer.
The internalized records are passed on to various backends, which extract information from a subset of the records and generate one or more output files.
These output files are typically .inc files for C++, but may be any type of file that the backend developer needs.
Resources for learning the language:
- TableGen Overview
- Programmer's reference guide
- Tutorial
- Tools for Learning LLVM TableGen
- Lessons in TableGen (video), slides
- Improving Your TableGen Descriptions (video), slides
Writing TableGen backends:
- TableGen Backend Developer's Guide
- How to write a TableGen backend (video), slides, also available as a notebook.
TableGen in MLIR:
Useful tools: