yonghong-song added a comment.
For the first example, actually clang is smart enough to remove all dead code,
so nothing generated.
[yhs@devbig003.ftw2 ~/tmp/ext_func_var]$ cat t1.c
extern void f1();
void f2(void *);
inline void f3() {
f2(f1);
}
[yhs@devbig003.ftw2 ~/tmp/ext_func_var]$ clang -target bpf -g -S -emit-llvm t1.c
[yhs@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@devbig003.ftw2 ~/tmp/ext_func_var]$
For the second example,
[yhs@devbig003.ftw2 ~/tmp/ext_func_var]$ cat t2.c
void f1();
int main() {
int x = sizeof(&f1);
return x;
}
[yhs@devbig003.ftw2 ~/tmp/ext_func_var]$ clang -target bpf -g -S -emit-llvm
t2.c
[yhs@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.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D100567/new/
https://reviews.llvm.org/D100567
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