> On Mar 4, 2016, at 2:00 PM, Robinson, Paul > <paul_robin...@playstation.sony.com> wrote: > > I tried a CU with an int variable instead of float, and enough other > stuff to keep it from being optimized away completely. > gcc produced DW_OP_reg3, while Clang produced "DW_OP_reg3; DW_OP_piece 4" > for the same variable. > > DW_OP_piece is really meant for assembling partial values in different > places, not subdividing a register.
I agree! I’ve been wanting to clean this up for a while now, I hope I’ll get to this soon. thanks everyone for your feedback! adrian > --paulr > >> -----Original Message----- >> From: Dwarf-Discuss [mailto:dwarf-discuss-boun...@lists.dwarfstd.org] On >> Behalf Of Adrian Prantl >> Sent: Friday, March 04, 2016 1:13 PM >> To: dwarf-discuss@lists.dwarfstd.org >> Subject: [Dwarf-Discuss] Representing the location of smaller values in >> vector registers >> >> I have a best-practice kind of question: >> >> The x86_64 System V ABI passes floating point values in the xmm0, xmm1, >> ... 128-bit SSE vector registers. I’m wondering what the correct DWARF v4 >> (lacking the DWARF 5 type conversions) expression for a 32-bit float in >> xmm0 is. >> >> Given the following program: >> >> float return_float() __attribute__((noinline)) { return 3.14f; } >> >> int main(int argc, char** argv) { >> float f = return_float(); >> return (int)f; >> } >> >> Clang (-O1) currently produces the following DWARF for the variable f: >> >> DW_TAG_variable >> DW_AT_location( reg17 ) // xmm0 = 17 >> DW_AT_name( "f" ) >> DW_AT_decl_file( "test.c" ) >> DW_AT_decl_line( 8 ) >> DW_AT_type( {0x0000004a} ( float ) ) >> >> Which causes LLDB to complain that the size of register xmm0 (128 Bits) is >> different from the size of f (32 Bits). I wonder who is wrong? Is LLDB >> being too strict, or should clang actually emit something like DW_OP_reg >> 17 (xmm0) DW_OP_piece 4 to make it abundantly clear that only the lower 32 >> bits of the vector register are interesting? >> >> -- adrian >> _______________________________________________ >> Dwarf-Discuss mailing list >> Dwarf-Discuss@lists.dwarfstd.org >> http://lists.dwarfstd.org/listinfo.cgi/dwarf-discuss-dwarfstd.org _______________________________________________ Dwarf-Discuss mailing list Dwarf-Discuss@lists.dwarfstd.org http://lists.dwarfstd.org/listinfo.cgi/dwarf-discuss-dwarfstd.org
