[all-commits] [llvm/llvm-project] e53ccb: [LLVM][MC] Introduce `OrFail` variants of MCD ops ...

[Rahul Joshi via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: e53ccb78e46c6d923fee914b31d13d930021a954
      https://github.com/llvm/llvm-project/commit/e53ccb78e46c6d923fee914b31d13d930021a954
  Author: Rahul Joshi <rjoshi at nvidia.com>
  Date:   2025-06-05 (Thu, 05 Jun 2025)

  Changed paths:
    M llvm/include/llvm/MC/MCDecoderOps.h
    M llvm/lib/Target/AArch64/CMakeLists.txt
    M llvm/test/TableGen/VarLenDecoder.td
    M llvm/test/TableGen/trydecode-emission.td
    M llvm/test/TableGen/trydecode-emission2.td
    M llvm/test/TableGen/trydecode-emission3.td
    M llvm/test/TableGen/trydecode-emission4.td
    M llvm/utils/TableGen/DecoderEmitter.cpp
    M utils/bazel/llvm-project-overlay/llvm/BUILD.bazel

  Log Message:
  -----------
  [LLVM][MC] Introduce `OrFail` variants of MCD ops (#138614)

Introduce `OrFail` variants for all MCD Decoder Ops that have
`NumToSKip` encoded with them. This is intended to capture the common
case of jumps to the end of the decoder table which has a `OP_Fail` at
the end. Using the `OrFail` variants of these ops avoid encoding the
`NumToSkip` jump offset for these cases, resulting in a reduction in the
size of the decoder tables (from 5 - 17%). Additionally, for the AArch64
target, the table size reduces enough to switch to using 2-byte
`NumToSkip` encoding instead of existing 3-bytes, resulting in a net 30%
reduction in the size of the decoder table.

The total reduction in the size of the decoder tables for different
targets is as follows (computed using the following command: `for i in
*.inc; do echo -n ``basename $i: ``; grep "MCD::OPC_Fail," $i | awk
'{sum += $2} END { print sum}'; done`)

```
Target         Old Size   New Size   % Reduction
================================================
AArch64           153268     106987       30.20
AMDGPU            412056     340856       17.28
ARC                 5061       4605        9.01
ARM                73831      60847       17.59
AVR                 1306       1158       11.33
BPF                 1927       1795        6.85
CSKY                8692       6922       20.36
Hexagon            41965      34759       17.17
Lanai                982        924        5.91
LoongArch          21629      20035        7.37
M68k               13461      11689       13.16
MSP430              3716       3384        8.93
Mips               31415      25771       17.97
PPC                28931      24771       14.38
RISCV              34800      28352       18.53
Sparc               7432       6236       16.09
SystemZ            32248      29716        7.85
VE                 42873      36923       13.88
XCore               2316       2196        5.18
Xtensa              3443       2793       18.88
```



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