[llvm-bugs] [Bug 45775] New: Differences in DWARF line number info between directly generated and assembled object files

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=45775

            Bug ID: 45775
           Summary: Differences in DWARF line number info between directly
                    generated and assembled object files
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: normal
          Priority: P
         Component: LLVM assembly language parser
          Assignee: unassignedbugs at nondot.org
          Reporter: Wolfgang_Pieb at playstation.sony.com
                CC: llvm-bugs at lists.llvm.org

The following source, when compiled directly to an object file vs. when first
compiled to an assembly file, and then assembled, produces different line
number information.

struct Ctx
{
  int m1;
  int m2;
};

static Ctx States[2] =
{
  {0, 1}, {2, 3}
};

int getType(struct s* myS);
int foo(struct s* myS)
{
  int type = getType(myS);
  if (type != -1) {
    return States[type].m2;
  }
  return 0;
}

The difference can be demonstrated with the following script:

#!/bin/sh
clang -g -O2 -c test.cpp -o test.o
clang -g -O2 -S test.cpp -o test.s
clang -g -c test.s -o test.assembled.o

objdump -WliarfsoR test.o > 1
objdump -WliarfsoR test.assembled.o > 2
diff 1 2


I'm seeing the following differences:
265c237
<   Length:                      87
---
>   Length:                      88
319,322c291,295
<   [0x00000053]  Advance Line by 20 to 20
<   [0x00000055]  Special opcode 33: advance Address by 2 to 0x18 and Line by 0
to 20
<   [0x00000056]  Advance PC by 2 to 0x1a
<   [0x00000058]  Extended opcode 1: End of Sequence
---
>   [0x00000053]  Set is_stmt to 1
>   [0x00000054]  Advance Line by 20 to 20
>   [0x00000056]  Special opcode 33: advance Address by 2 to 0x18 and Line by 0 to 20
>   [0x00000057]  Advance PC by 2 to 0x1a
>   [0x00000059]  Extended opcode 1: End of Sequence

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