On Tue, Sep 17, 2019 at 4:33 PM Richard Sandiford
<richard.sandif...@arm.com> wrote:
>
> assemble_real used GEN_INT to create integers directly from the
> longs returned by real_to_target. assemble_integer then went on
> to interpret the const_ints as though they had the mode corresponding
> to the accompanying size parameter:
>
> imode = mode_for_size (size * BITS_PER_UNIT, mclass, 0).require ();
>
> for (i = 0; i < size; i += subsize)
> {
> rtx partial = simplify_subreg (omode, x, imode, i);
>
> But in the assemble_real case, X might not be canonical for IMODE.
>
> If the interface to assemble_integer is supposed to allow outputting
> (say) the low 4 bytes of a DImode integer, then the simplify_subreg
> above is wrong. But if the number of bytes passed to assemble_integer
> is supposed to be the number of bytes that the integer actually contains,
> assemble_real is wrong.
>
> This patch takes the latter interpretation and makes assemble_real
> generate const_ints that are canonical for the number of bytes passed.
>
> The flip_storage_order handling assumes that each long is a full
> SImode, which e.g. excludes BITS_PER_UNIT != 8 and float formats
> whose memory size is not a multiple of 32 bits (which includes
> HFmode at least). The patch therefore leaves that code alone.
> If interpreting each integer as SImode is correct, the const_ints
> that it generates are also correct.
>
> Tested on aarch64-linux-gnu and x86_64-linux-gnu. Also tested
> by making sure that there were no new errors from a range of
> cross-built targets. OK to install?
>
> Richard
>
>
> 2019-09-17 Richard Sandiford <richard.sandif...@arm.com>
>
> gcc/
> * varasm.c (assemble_real): Generate canonical const_ints.
>
> Index: gcc/varasm.c
> ===================================================================
> --- gcc/varasm.c 2019-09-05 08:49:30.829739618 +0100
> +++ gcc/varasm.c 2019-09-17 15:30:10.400740515 +0100
> @@ -2873,25 +2873,27 @@ assemble_real (REAL_VALUE_TYPE d, scalar
> real_to_target (data, &d, mode);
>
> /* Put out the first word with the specified alignment. */
> + unsigned int chunk_nunits = MIN (nunits, units_per);
> if (reverse)
> elt = flip_storage_order (SImode, gen_int_mode (data[nelts - 1],
> SImode));
> else
> - elt = GEN_INT (data[0]);
> - assemble_integer (elt, MIN (nunits, units_per), align, 1);
> - nunits -= units_per;
> + elt = GEN_INT (sext_hwi (data[0], chunk_nunits * BITS_PER_UNIT));
why the appearant difference between the storage-order flipping
variant using gen_int_mode vs. the GEN_INT with sext_hwi?
Can't we use gen_int_mode in the non-flipping path and be done with that?
> + assemble_integer (elt, chunk_nunits, align, 1);
> + nunits -= chunk_nunits;
>
> /* Subsequent words need only 32-bit alignment. */
> align = min_align (align, 32);
>
> for (int i = 1; i < nelts; i++)
> {
> + chunk_nunits = MIN (nunits, units_per);
> if (reverse)
> elt = flip_storage_order (SImode,
> gen_int_mode (data[nelts - 1 - i], SImode));
> else
> - elt = GEN_INT (data[i]);
> - assemble_integer (elt, MIN (nunits, units_per), align, 1);
> - nunits -= units_per;
> + elt = GEN_INT (sext_hwi (data[i], chunk_nunits * BITS_PER_UNIT));
> + assemble_integer (elt, chunk_nunits, align, 1);
> + nunits -= chunk_nunits;
> }
> }
>
