[Bug debug/99388] Invalid debug info for __fp16

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99388

--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-8 branch has been updated by Jakub Jelinek
<jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:dbdd062665903c88b89525573d7dfde233562e8c

commit r8-10898-gdbdd062665903c88b89525573d7dfde233562e8c
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Sun Mar 21 17:27:39 2021 +0100

    dwarf2out: Fix debug info for 2 byte floats [PR99388]

    Aarch64, ARM and a couple of other architectures have 16-bit floats,
HFmode.
    As can be seen e.g. on
    void
    foo (void)
    {
      __fp16 a = 1.0;
      asm ("nop");
      a = 2.0;
      asm ("nop");
      a = 3.0;
      asm ("nop");
    }
    testcase, GCC mishandles this on the dwarf2out.c side by assuming all
    floating point types have sizes in multiples of 4 bytes, so what GCC emits
    is it says that e.g. the DW_OP_implicit_value will be 2 bytes but then
    doesn't emit anything and so anything emitted after it is treated by
    consumers as the value and then they get out of sync.
    real_to_target which insert_float uses indeed fills it that way, but
putting
    into an array of long 32 bits each time, but for the half floats it puts
    everything into the least significant 16 bits of the first long no matter
    what endianity host or target has.

    The following patch fixes it.  With the patch the -g -O2 -dA output changes
    (in a cross without .uleb128 support):
            .byte   0x9e    // DW_OP_implicit_value
            .byte   0x2     // uleb128 0x2
    +       .2byte  0x3c00  // fp or vector constant word 0
            .byte   0x7     // DW_LLE_start_end (*.LLST0)
            .8byte  .LVL1   // Location list begin address (*.LLST0)
            .8byte  .LVL2   // Location list end address (*.LLST0)
            .byte   0x4     // uleb128 0x4; Location expression size
            .byte   0x9e    // DW_OP_implicit_value
            .byte   0x2     // uleb128 0x2
    +       .2byte  0x4000  // fp or vector constant word 0
            .byte   0x7     // DW_LLE_start_end (*.LLST0)
            .8byte  .LVL2   // Location list begin address (*.LLST0)
            .8byte  .LFE0   // Location list end address (*.LLST0)
            .byte   0x4     // uleb128 0x4; Location expression size
            .byte   0x9e    // DW_OP_implicit_value
            .byte   0x2     // uleb128 0x2
    +       .2byte  0x4200  // fp or vector constant word 0
            .byte   0       // DW_LLE_end_of_list (*.LLST0)

    Bootstrapped/regtested on x86_64-linux, aarch64-linux and
    armv7hl-linux-gnueabi, ok for trunk?

    I fear the CONST_VECTOR case is still broken, while HFmode elements of
vectors
    should be fine (it uses eltsize of the element sizes) and likewise SFmode
could
    be fine, DFmode vectors are emitted as two 32-bit ints regardless of
endianity
    and I'm afraid it can't be right on big-endian.  But I haven't been able to
    create a testcase that emits a CONST_VECTOR, for e.g. unused vector vars
    with constant operands we emit CONCATN during expansion and thus ...
    DW_OP_*piece for each element of the vector and for
    DW_TAG_call_site_parameter we give up (because we handle CONST_VECTOR only
    in loc_descriptor, not mem_loc_descriptor).

    2021-03-21  Jakub Jelinek  <jakub@redhat.com>

            PR debug/99388
            * dwarf2out.c (insert_float): Change return type from void to
            unsigned, handle GET_MODE_SIZE (mode) == 2 and return element size.
            (mem_loc_descriptor, loc_descriptor, add_const_value_attribute):
            Adjust callers.

    (cherry picked from commit d3dd3703f1d42b14c88b91e51a2a775fe00a2974)