de6fad5146
The current implementation considers both iPTR+iN and everything else all in one go, which leads to more special casing when iPTR is present in only one set than is described in the comment block. Moreover this makes it very difficult to add any new iPTR-like wildcards due to the exponential combinatorial explosion that occurs. Logically, iPTR+iN handling is entirely independent from everything else, so rewrite the code to do them separately. This removes special cases, making the core of the implementation more succinct, whilst more clearly implementing exactly what is described in the comment block, and allows for any number of (non-overlapping) wildcards to be added to the list, as needed by CHERI LLVM downstream (due to having a new capability type which, much like a normal integer pointer in LLVM, varies in size between targets and modes). In testing, this change results in identical TableGen output for all in-tree backends (including those in LLVM_ALL_EXPERIMENTAL_TARGETS), and it is intended that this implementation is entirely equivalent to the old one.
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: