On 10/24/23 11:58, Richard Sandiford wrote:
The first in-tree use of RTL-SSA was fwprop, and one of the goals
was to make the fwprop rewrite preserve the old behaviour as far
as possible. The switch to RTL-SSA was supposed to be a pure
infrastructure change. So RTL-SSA has various FIXMEs for things
that were artifically limited to faciliate the old-fwprop vs.
new-fwprop comparison.
One of the things that fwprop wants to do is extend live ranges, and
function_info::make_use_available tried to keep within the cases that
old fwprop could handle.
Since the information is built in extended basic blocks, it's easy
to handle intra-EBB queries directly. This patch does that, and
removes the associated FIXME.
To get a flavour for how much difference this makes, I tried compiling
the testsuite at -Os for at least one target per supported CPU and OS.
For most targets, only a handful of tests changed, but the vast majority
of changes were positive. The only target that seemed to benefit
significantly was i686-apple-darwin.
The main point of the patch is to remove the FIXME and to enable
the upcoming post-RA late-combine pass to handle more cases.
gcc/
* rtl-ssa/functions.h (function_info::remains_available_at_insn):
New member function.
* rtl-ssa/accesses.cc (function_info::remains_available_at_insn):
Likewise.
(function_info::make_use_available): Avoid false negatives for
queries within an EBB.
OK
jeff
