[PATCH] D92842: [SelectionDAG] Add Target-Independent Compiler Barrier

[Kan Shengchen via Phabricator via llvm-commits]

skan added a comment.

In D92842#2570304 <https://reviews.llvm.org/D92842#2570304>, @skan wrote:

> In D92842#2561721 <https://reviews.llvm.org/D92842#2561721>, @lenary wrote:
>
>> Can you link to the bug you are referencing? With a bug to point to, it'll be easier to push for this to land.
>
> The failed LIT tests in the remote tests are "x64 debian > LLVM.CodeGen/RISCV::atomic-fence.ll",  "x64 windows > LLVM.CodeGen/RISCV::atomic-fence.ll", "x64 windows > LLVM.CodeGen/XCore::threads.ll", I think you can see them on this page.
>
> The bug "X86::Int_MemBarrier should be a MetaInstruction" is an //internal// bug, I found it when I was doing some development work about debug info personally.  Although I could not give a failed test, here is a way to trigger that:
>
>   define dso_local i32 @main() !dbg !7 {
>   entry:
>     fence acquire, !dbg !9
>     fence release, !dbg !9
>     %retval = alloca i32, align 4
>     store i32 0, i32* %retval, align 4
>     ret i32 0, !dbg !9
>   }
>   
>   !llvm.dbg.cu = !{!0}
>   !llvm.module.flags = !{!3, !4, !5}
>   !llvm.ident = !{!6}
>   
>   !0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 11.0.0", isOptimized: false, runtimeVersion: 0, emissionKind: DebugDirectivesOnly, enums: !2, splitDebugInlining: false, nameTableKind: None)
>   !1 = !DIFile(filename: "none.c", directory: "/temp")
>   !2 = !{}
>   !3 = !{i32 2, !"PersonalFlag", i32 1}
>   !4 = !{i32 2, !"Debug Info Version", i32 3}
>   !5 = !{i32 1, !"wchar_size", i32 4}
>   !6 = !{!"clang version 11.0.0"}
>   !7 = distinct !DISubprogram(name: "main", scope: !1, file: !1, line: 1, type: !8, scopeLine: 1, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !2)
>   !8 = !DISubroutineType(types: !2)
>   !9 = !DILocation(line: 1, column: 14, scope: !7)
>
>
>
>   llc -O0 -mtriple x86_64-linux-gnu  test.ll
>
> IR `fence acquire` and `fence release` is lowered to  `X86::Int_MemBarrier`,  and the interface `bool isMetaInstruction() const` returns //false// for it. So if you add an assert
> for this, the program will crash.

A LIT test is provided at D121879 <https://reviews.llvm.org/D121879>.


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