[llvm] [BPF] Handle unreachable with a unimplemented kfunc call (PR #131731)

[via llvm-commits]

yonghong-song wrote:

I will add some tests in the next revision.

> Maybe consider adding a test case? E.g. as below:
> 
> ```llvm
> ; RUN: llc -mtriple=bpfel -mcpu=v3 -filetype=obj -o %t1 %s
> ; RUN: llvm-objcopy --dump-section='.BTF'=%t2 %t1
> ; RUN: %python %p/print_btf.py %t2 | FileCheck -check-prefixes=CHECK-BTF %s
> ; RUN: llc -mtriple=bpfel -mcpu=v3 < %s | FileCheck -check-prefixes=CHECK %s
> 
> define void @foo() {
> entry:
>   tail call void @bar()
>   unreachable
> }
> 
> ; CHECK:      foo:
> ; CHECK-NEXT: .Lfunc_begin0:
> ; CHECK-NEXT:   .cfi_startproc
> ; CHECK-NEXT: # %bb.0:
> ; CHECK-NEXT:    call bar
> ; CHECK-NEXT:    call __unreachable_helper
> ; CHECK-NEXT: .Lfunc_end0:
> 
> define void @buz() #0 {
> entry:
>   tail call void asm sideeffect "r0 = r1; exit;", ""()
>   unreachable
> }

As suggested by @nikic, I will later have a patch to prevent 'unreachable' for naked functions for all architectures. So this test will not be included.

> 
> ; CHECK: buz:
> ; CHECK-NEXT: .Lfunc_begin1:
> ; CHECK-NEXT:   .cfi_startproc
> ; CHECK-NEXT: # %bb.0:
> ; CHECK-NEXT:   #APP
> ; CHECK-NEXT:   r0 = r1
> ; CHECK-NEXT:   exit
> ; CHECK-EMPTY:
> ; CHECK-NEXT:   #NO_APP
> ; CHECK-NEXT: .Lfunc_end1:
> 
> ; CHECK-BTF: [1] FUNC_PROTO '(anon)' ret_type_id=0 vlen=0
> ; CHECK-BTF: [2] FUNC '__unreachable_helper' type_id=1 linkage=extern
> ; CHECK-BTF: [3] DATASEC '.ksyms' size=0 vlen=1
> ; CHECK-BTF:  type_id=2 offset=0 size=0
> 
> declare dso_local void @bar()
> 
> attributes #0 = { naked }
> 
> !llvm.dbg.cu = !{!0}
> !llvm.module.flags = !{!2, !3}
> 
> !0 = distinct !DICompileUnit(language: DW_LANG_C11, file: !1, emissionKind: FullDebug)
> !1 = !DIFile(filename: "test.c", directory: "/some/dir")
> !2 = !{i32 7, !"Dwarf Version", i32 5}
> !3 = !{i32 2, !"Debug Info Version", i32 3}
> ```



https://github.com/llvm/llvm-project/pull/131731