[llvm] [AMDGPU][GlobalISel] Implement missing rules for G_TRUNC legalization (PR #180647)

[Anshil Gandhi via llvm-commits]

gandhi56 wrote:

> > I tried a few different filter regexes, including "COPY" and "LOAD". An issue is that it does not realize missing definitions.
> 
> I was trying this out, it is kind of difficult to write regex, and it turns out that in mir only filter-out-after works since other options end up removing lines and we end up with referencing something that does not exist. This leaves us with trunc as last line. I came up with this with help of claude
> 
> 1. UTC_ARGS line:
>    ; NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --filter-out-after "debug-location" --version 6
> 2. All 16 trunc instructions tagged with !dbg !4:
>    %trunc = trunc  %val to , !dbg !4
> 3. Metadata appended at end of file:
>    !llvm.dbg.cu = !{!0}
>    !llvm.module.flags = !{!2}
> 
> !0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1) !1 = !DIFile(filename: ".", directory: ".") !2 = !{i32 2, !"Debug Info Version", i32 3} !3 = distinct !DISubprogram(name: "trunc", scope: !1, file: !1, line: 1, unit: !0) !4 = !DILocation(line: 1, scope: !3)
> 
> Regenerate command: llvm/utils/update_mir_test_checks.py --llc-binary build_clang/bin/llc --force-update llvm/test/CodeGen/AMDGPU/GlobalISel/trunc-brc.ll
> 
> Note: --filter-out-after "debug-location" does NOT need to be passed on the command line. update_mir_test_checks.py reads UTC_ARGS directly from the NOTE line in the test file and applies them automatically.

That's an impressively neat solution!

https://github.com/llvm/llvm-project/pull/180647