[PATCH] D100567: BPF: emit debuginfo for Function of DeclRefExpr if requested

[Yonghong Song via Phabricator via cfe-commits]

yonghong-song added a comment.

For the first example, actually clang is smart enough to remove all dead code, so nothing generated.

[yhs at devbig003.ftw2 ~/tmp/ext_func_var]$ cat t1.c
extern void f1();
void f2(void *);
inline void f3() {

  f2(f1);

}
[yhs at devbig003.ftw2 ~/tmp/ext_func_var]$ clang -target bpf -g -S -emit-llvm t1.c
[yhs at devbig003.ftw2 ~/tmp/ext_func_var]$ cat t1.ll
; ModuleID = 't1.c'
source_filename = "t1.c"
target datalayout = "e-m:e-p:64:64-i64:64-i128:128-n32:64-S128"
target triple = "bpf"

!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 13.0.0 (https://github.com/llvm/llvm-project.git 68275c77c92b89fafbacc31b4f40303bb9e0c9a7)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, splitDebugInlining: false, nameTableKind: None)
!1 = !DIFile(filename: "t1.c", directory: "/home/yhs/tmp/ext_func_var")
!2 = !{}
!3 = !{i32 7, !"Dwarf Version", i32 4}
!4 = !{i32 2, !"Debug Info Version", i32 3}
!5 = !{i32 1, !"wchar_size", i32 4}
!6 = !{!"clang version 13.0.0 (https://github.com/llvm/llvm-project.git 68275c77c92b89fafbacc31b4f40303bb9e0c9a7)"}
[yhs at devbig003.ftw2 ~/tmp/ext_func_var]$

For the second example,

[yhs at devbig003.ftw2 ~/tmp/ext_func_var]$ cat t2.c                                                                   
void f1();                                                                                                          
int main() {

  int x = sizeof(&f1);                                                                                              
  return x;                                                                                                         

}                                                                                                                   
[yhs at devbig003.ftw2 ~/tmp/ext_func_var]$ clang -target bpf -g -S -emit-llvm t2.c                                    
[yhs at devbig003.ftw2 ~/tmp/ext_func_var]$ cat t2.ll                                                                  
; ModuleID = 't2.c'                                                                                                 
source_filename = "t2.c"                                                                                            
target datalayout = "e-m:e-p:64:64-i64:64-i128:128-n32:64-S128"                                                     
target triple = "bpf"

                                      

; Function Attrs: noinline nounwind optnone                                                                         
define dso_local i32 @main() #0 !dbg !7 {                                                                           
entry:

  %retval = alloca i32, align 4                                                                                     
  %x = alloca i32, align 4                                                                                          
  store i32 0, i32* %retval, align 4                                                                                
  call void @llvm.dbg.declare(metadata i32* %x, metadata !11, metadata !DIExpression()), !dbg !12                   
  store i32 8, i32* %x, align 4, !dbg !12                                                                           
  %0 = load i32, i32* %x, align 4, !dbg !13                                                                         
  ret i32 %0, !dbg !14                                                                                              

}

; Function Attrs: nofree nosync nounwind readnone speculatable willreturn
declare void @llvm.dbg.declare(metadata, metadata, metadata) #1

attributes #0 = { noinline nounwind optnone "frame-pointer"="all" "min-legal-vector-width"="0" "no-trapping-math"="t
rue" "stack-protector-buffer-size"="8" }
attributes #1 = { nofree nosync nounwind readnone speculatable willreturn }

!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 13.0.0 (https://github.com/ll
vm/llvm-project.git 68275c77c92b89fafbacc31b4f40303bb9e0c9a7)", isOptimized: false, runtimeVersion: 0, emissionKind:
 FullDebug, enums: !2, splitDebugInlining: false, nameTableKind: None)
!1 = !DIFile(filename: "t2.c", directory: "/home/yhs/tmp/ext_func_var")
!2 = !{}
!3 = !{i32 7, !"Dwarf Version", i32 4}
!4 = !{i32 2, !"Debug Info Version", i32 3}
!5 = !{i32 1, !"wchar_size", i32 4}
!6 = !{!"clang version 13.0.0 (https://github.com/llvm/llvm-project.git 68275c77c92b89fafbacc31b4f40303bb9e0c9a7)"}
!7 = distinct !DISubprogram(name: "main", scope: !1, file: !1, line: 2, type: !8, scopeLine: 2, spFlags: DISPFlagDef
inition, unit: !0, retainedNodes: !2)
!8 = !DISubroutineType(types: !9)
!9 = !{!10}
!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
!11 = !DILocalVariable(name: "x", scope: !7, file: !1, line: 3, type: !10)
!12 = !DILocation(line: 3, column: 7, scope: !7)
!13 = !DILocation(line: 4, column: 10, scope: !7)
!14 = !DILocation(line: 4, column: 3, scope: !7)

The debuginfo for "f1" is not generated for case "sizeof(&f1);". I think it is okay in this case as in most cases, people wants debuginfo only if that pointer ptr appears in generated code.


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https://reviews.llvm.org/D100567