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This patch adds a new option `-aarch64-enable-zpr-predicate-spills` (which is disabled by default), this option replaces predicate spills with vector spills in streaming[-compatible] functions. For example: ``` str p8, [sp, #7, mul vl] // 2-byte Folded Spill // ... ldr p8, [sp, #7, mul vl] // 2-byte Folded Reload ``` Becomes: ``` mov z0.b, p8/z, #1 str z0, [sp] // 16-byte Folded Spill // ... ldr z0, [sp] // 16-byte Folded Reload ptrue p4.b cmpne p8.b, p4/z, z0.b, #0 ``` This is done to avoid streaming memory hazards between FPR/vector and predicate spills, which currently occupy the same stack area even when the `-aarch64-stack-hazard-size` flag is set. This is implemented with two new pseudos SPILL_PPR_TO_ZPR_SLOT_PSEUDO and FILL_PPR_FROM_ZPR_SLOT_PSEUDO. The expansion of these pseudos handles scavenging the required registers (z0 in the above example) and, in the worst case spilling a register to an emergency stack slot in the expansion. The condition flags are also preserved around the `cmpne` in case they are live at the expansion point.
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: