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Optimise CONCAT handling in emit_group_load

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The CONCAT handling in emit_group_load chooses between doing
an extraction from a single component or forcing the whole
thing to memory and extracting from there.  The condition for
the former (more efficient) option was:

	  if ((bytepos == 0 && bytelen == slen0)
	      || (bytepos != 0 && bytepos + bytelen <= slen))

On the one hand this seems dangerous, since the second line
allows bit ranges that start in the first component and leak
into the second.  On the other hand it seems strange to allow
references that start after the first byte of the second
component but not those that start after the first byte
of the first component.  This led to a pessimisation of
things like gcc.dg/builtins-54.c for hppa64-hp-hpux11.23.

This patch simply checks whether the reference is contained
within a single component.  It also makes sure that we do
an extraction on anything that doesn't span the whole
component (even if it's constant).

gcc/
2016-11-15  Richard Sandiford  <richard.sandiford@arm.com>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

	* expr.c (emit_group_load_1): Tighten check for whether an
	access involves only one operand of a CONCAT.  Use extract_bit_field
	for constants if the bit range does span the whole operand.

Co-Authored-By: Alan Hayward <alan.hayward@arm.com>
Co-Authored-By: David Sherwood <david.sherwood@arm.com>

From-SVN: r242477
This commit is contained in:
Richard Sandiford 2016-11-16 10:21:22 +00:00 committed by Richard Sandiford
parent 0e0af68921
commit 024f701ca1
2 changed files with 17 additions and 6 deletions
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8
gcc/ChangeLog
View File

@ -1,3 +1,11 @@
2016-11-16 Richard Sandiford <richard.sandiford@arm.com>
Alan Hayward <alan.hayward@arm.com>
David Sherwood <david.sherwood@arm.com>
* expr.c (emit_group_load_1): Tighten check for whether an
access involves only one operand of a CONCAT. Use extract_bit_field
for constants if the bit range does span the whole operand.
2016-11-16 Richard Sandiford <richard.sandiford@arm.com>
Alan Hayward <alan.hayward@arm.com>
David Sherwood <david.sherwood@arm.com>

15
gcc/expr.c
View File

@ -2175,19 +2175,22 @@ emit_group_load_1 (rtx *tmps, rtx dst, rtx orig_src, tree type, int ssize)
{
unsigned int slen = GET_MODE_SIZE (GET_MODE (src));
unsigned int slen0 = GET_MODE_SIZE (GET_MODE (XEXP (src, 0)));
unsigned int elt = bytepos / slen0;
unsigned int subpos = bytepos % slen0;
if ((bytepos == 0 && bytelen == slen0)
|| (bytepos != 0 && bytepos + bytelen <= slen))
if (subpos + bytelen <= slen0)
{
/* The following assumes that the concatenated objects all
have the same size. In this case, a simple calculation
can be used to determine the object and the bit field
to be extracted. */
tmps[i] = XEXP (src, bytepos / slen0);
if (! CONSTANT_P (tmps[i])
&& (!REG_P (tmps[i]) || GET_MODE (tmps[i]) != mode))
tmps[i] = XEXP (src, elt);
if (subpos != 0
|| subpos + bytelen != slen0
|| (!CONSTANT_P (tmps[i])
&& (!REG_P (tmps[i]) || GET_MODE (tmps[i]) != mode)))
tmps[i] = extract_bit_field (tmps[i], bytelen * BITS_PER_UNIT,
(bytepos % slen0) * BITS_PER_UNIT,
subpos * BITS_PER_UNIT,
1, NULL_RTX, mode, mode, false);
}
else