[llvm-dev] Understanding how to use of debugger intrinsic functions

[Peng Yu via llvm-dev]

I see debugger intrinsic functions like @llvm.dbg.declare appear in
the .ll generated with -g. But I still don't understand how it is
used.

https://llvm.org/docs/SourceLevelDebugging.html#debugger-intrinsic-functions

For the following C program, I got the relevant text in the .ll file
pasted below and the relevant metadata (listed using depth-first
search).

Does @llvm.dbg.declare actually translate to some machine code similar
to other user-defined functions? It seems that it only describes the
data types. Will they be translated to a native debugging format to
store along with the executable?

Can they be used for binary instrumentations? Thanks.

//////
#include <stdio.h>

int f(int i) {
    return i + 1;
}

int main(int argc, char *argv[1]) {
    if(f(argc)) {
        puts("Hello World!");
    }
    return 0;
}
//////

define i32 @main(i32 %arg, i8** %arg1) #0 !dbg !17 {
...
  store i32 %arg, i32* %tmp2, align 4
  call void @llvm.dbg.declare(metadata i32* %tmp2, metadata !23,
metadata !DIExpression()), !dbg !24
 ...

!23 = !DILocalVariable(name: "argc", arg: 1, scope: !17, file: !1,
line: 8, type: !11)

!17 = distinct !DISubprogram(name: "main", scope: !1, file: !1, line:
8, type: !18, isLocal: false, isDefinition: true, scopeLine: 8, flags:
DIFlagPrototyped, isOptimized: false, unit: !0, retainedNodes: !2)
!1 = !DIFile(filename: "../test_data/main.c", directory:
"/Users/pengy/linux/bin/wrappercomposite/src/xplat/llvmxplat/src/lvll2/lvll2fundbi/llin2funbodyraw0/main")
!18 = !DISubroutineType(types: !19)
!19 = !{!11, !11, !20}
!11 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
!20 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !21, size: 64)
!21 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !22, size: 64)
!22 = !DIBasicType(name: "char", size: 8, encoding: DW_ATE_signed_char)

!24 = !DILocation(line: 8, column: 14, scope: !17)

-- 
Regards,
Peng