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Make assemble_real generate canonical CONST_INTs 

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.

2019-09-18  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* varasm.c (assemble_real): Generate canonical const_ints.

From-SVN: r275873
This commit is contained in:
Richard Sandiford 2019-09-18 11:37:02 +00:00 committed by Richard Sandiford
parent a3d0946904
commit 743a16d57a
2 changed files with 12 additions and 6 deletions
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4
gcc/ChangeLog
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@ -1,3 +1,7 @@
2019-09-18 Richard Sandiford <richard.sandiford@arm.com>
* varasm.c (assemble_real): Generate canonical const_ints.
2019-09-18 Richard Biener <rguenther@suse.de>
PR lto/91763

14
gcc/varasm.c
View File

@ -2873,25 +2873,27 @@ assemble_real (REAL_VALUE_TYPE d, scalar_float_mode mode, unsigned int align,
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));
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;
}
}