r242094 - /branches/ARM/sve-branch/gcc/expr.c

[rsandifo at gcc dot gnu dot org]

Author: rsandifo
Date: Fri Nov 11 16:58:23 2016
New Revision: 242094

URL: https://gcc.gnu.org/viewcvs?rev=242094&root=gcc&view=rev
Log:
Optimise CONCAT handling in emit_group_load

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).

Modified:
    branches/ARM/sve-branch/gcc/expr.c