[PATCH] D24425: DebugInfo: support for DWARFv5 DW_AT_alignment attribute

[Victor Leschuk via llvm-commits]

vleschuk marked 3 inline comments as done.
vleschuk added inline comments.


================
Comment at: lib/CodeGen/AsmPrinter/DwarfUnit.cpp:1415
       // is non-zero if and only if alignment was forced (e.g. _Alignas()),
       // which can't be done with bitfields. Thus we use FieldSize here.
       uint64_t AlignInBits = FieldSize;
----------------
aprantl wrote:
> What about packed structs?
> 
> Sorry, I'm just being very cautious about any changes here, because every single time I touched this code in that past I broke the either LLDB or GDB ;-)
> 
> A couple of examples from the testsuite you can run through clang with both -gdwarf-2 and -gdwarf-4 and verify that the DWARF output didn't change:
> 
> ```
> #pragma pack(1)
>     struct PackedBits
>      {
>         char a;
>         uint32_t b : 5,
>         c : 27
>       } s;
>    #pragma pack()
> 
>  struct bitfield {
>     int a : 2;
>     int b : 32;
>     int c : 1;
>     int d : 28;
> }
> 
> struct size8 {
>   int i : 4;
>   long long l : 60;
> };
> 
> 
> struct layout0 {
>   char l0_ofs0;
>   struct size8 l0_ofs8;
>   int l0_ofs16 : 1;
> };
> 
> struct size8_anon {
>   int : 4;
>   long long : 60;
> };
> struct layout1 {
>   char l1_ofs0;
>   struct size8_anon l1_ofs1;
>   int l1_ofs9 : 1;
> };
> 
> #pragma pack(1)
> struct size8_pack1 {
>   int i : 4;
>   long long l : 60;
> };
> struct layout2 {
>   char l2_ofs0;
>   struct size8_pack1 l2_ofs1;
>   int l2_ofs9 : 1;
> };
> #pragma pack()
> 
> #pragma pack(4)
> struct size8_pack4 {
>   int i : 4;
>   long long l : 60;
> };
> struct layout3 {
>   char l3_ofs0;
>   struct size8_pack4 l3_ofs4;
>   int l3_ofs12 : 1;
> };
> #pragma pack()
> 
> ```
> 
We already have test for that: DebugInfo/X86/debug-info-packed-struct.ll - its based on debug-info-packed-struct.c from clang (the one you quoted). I also manually checked this both with dwarf-2 and dwarf-4, dwarf output is the same for clang 3.9 release and current build with my changes.


https://reviews.llvm.org/D24425