> 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?
I would think that clang is right, and LLDB is wrong. It would be
silly to require the producer to use a longer representation that
essentially means the same thing. DW_OP_piece isn't meant to say that
you're only using part of the register -- it's meant for when part of
a larger *value* is in the register (whether the whole register or
part of it). Indeed, using DW_OP_piece leaves you in the same
situation -- with 32 bits placed in a 128-bit register.
How is this any different from saying a char variable is in a 32-bit register?
It's up to the ABI to define how smaller values are placed within a register.
-cary
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