Hello Richard:
On 09/11/23 6:21 pm, Richard Biener wrote:
> On Wed, Nov 8, 2023 at 4:00 PM Ajit Agarwal <aagar...@linux.ibm.com> wrote:
>>
>> tree-ssa-loop-ivopts : Add live analysis in regs used in decision making.
>>
>> Add live anaysis in regs used calculation in decision making of
>> selecting ivopts candidates.
>>
>> 2023-11-08 Ajit Kumar Agarwal <aagar...@linux.ibm.com>
>>
>> gcc/ChangeLog:
>>
>> * tree-ssa-loop-ivopts.cc (get_regs_used): New function.
>> (determine_set_costs): Call to get_regs_used to use live
>> analysis.
>> ---
>> gcc/tree-ssa-loop-ivopts.cc | 73 +++++++++++++++++++++++++++++++++++--
>> 1 file changed, 70 insertions(+), 3 deletions(-)
>>
>> diff --git a/gcc/tree-ssa-loop-ivopts.cc b/gcc/tree-ssa-loop-ivopts.cc
>> index c3336603778..e02fe7d434b 100644
>> --- a/gcc/tree-ssa-loop-ivopts.cc
>> +++ b/gcc/tree-ssa-loop-ivopts.cc
>> @@ -6160,6 +6160,68 @@ ivopts_estimate_reg_pressure (struct ivopts_data
>> *data, unsigned n_invs,
>> return cost + n_cands;
>> }
>>
>> +/* Return regs used based on live-in and liveout of given ssa variables. */
>
> Please explain how the following code relates to anything like "live
> analysis" and
> where it uses live-in and live-out. And what "live-in/out of a given
> SSA variable"
> should be.
>
> Also explain why you are doing this at all. The patch doesn't come
> with a testcase
> or with any other hint that motivated you.
>
> Richard.
>
The function get_regs_used increments the regs_used based on live-in
and live-out analysis of given ssa name. Instead of setting live-in and
live-out bitmap I increment the regs_used.
Below is how I identify live-in and live-out and increments the regs_used
variable:
a) For a given def_bb of gimple statement of ssa name there should be
live-out and increments the regs_used.
b) Visit each use of SSA_NAME and if it isn't in the same block as the def,
we identify live on entry blocks and increments regs_used.
The below function is the modification of set_var_live_on_entry of
tree-ssa-live.cc
Where we set the bitmap of liveout and livein of basic block. Instead of
setting bitmap, regs_used is incremented.
I identify regs_used as the number of live-in and liveout of given ssa name
variable.
For each iv candiate ssa variables I identify regs_used and take maximum of regs
used for all the iv candidates that will be used in
ivopts_estimate_register_pressure
cost analysis.
Motivation behind doing this optimization is I get good performance improvement
for several spec cpu 2017 benchmarks for FP and INT around 2% to 7%.
Also setting regs_used as number of iv candiates, which is not
optimized and robust way of decision making for ivopts optimization I decide
on live-in and live-out analysis which is more correct and appropriate way of
identifying regs_used.
And also there are no regressions in bootstrapped/regtested on
powerpc64-linux-gnu.
Thanks & Regards
Ajit
>> +static unsigned
>> +get_regs_used (tree ssa_name)
>> +{
>> + unsigned regs_used = 0;
>> + gimple *stmt;
>> + use_operand_p use;
>> + basic_block def_bb = NULL;
>> + imm_use_iterator imm_iter;
>> +
>> + stmt = SSA_NAME_DEF_STMT (ssa_name);
>> + if (stmt)
>> + {
>> + def_bb = gimple_bb (stmt);
>> + /* Mark defs in liveout bitmap temporarily. */
>> + if (def_bb)
>> + regs_used++;
>> + }
>> + else
>> + def_bb = ENTRY_BLOCK_PTR_FOR_FN (cfun);
>> +
>> + /* An undefined local variable does not need to be very alive. */
>> + if (virtual_operand_p (ssa_name)
>> + || ssa_undefined_value_p (ssa_name, false))
>> + return 0;
>> +
>> + /* Visit each use of SSA_NAME and if it isn't in the same block as the
>> def,
>> + add it to the list of live on entry blocks. */
>> + FOR_EACH_IMM_USE_FAST (use, imm_iter, ssa_name)
>> + {
>> + gimple *use_stmt = USE_STMT (use);
>> + basic_block add_block = NULL;
>> +
>> + if (gimple_code (use_stmt) == GIMPLE_PHI)
>> + {
>> + /* Uses in PHI's are considered to be live at exit of the SRC block
>> + as this is where a copy would be inserted. Check to see if it
>> is
>> + defined in that block, or whether its live on entry. */
>> + int index = PHI_ARG_INDEX_FROM_USE (use);
>> + edge e = gimple_phi_arg_edge (as_a <gphi *> (use_stmt), index);
>> + if (e->src != def_bb)
>> + add_block = e->src;
>> + }
>> + else if (is_gimple_debug (use_stmt))
>> + continue;
>> + else
>> + {
>> + /* If its not defined in this block, its live on entry. */
>> + basic_block use_bb = gimple_bb (use_stmt);
>> + if (use_bb != def_bb)
>> + add_block = use_bb;
>> + }
>> +
>> + /* If there was a live on entry use, increment register used. */
>> + if (add_block)
>> + {
>> + regs_used++;
>> + }
>> + }
>> + return regs_used;
>> +}
>> +
>> /* For each size of the induction variable set determine the penalty. */
>>
>> static void
>> @@ -6200,15 +6262,20 @@ determine_set_costs (struct ivopts_data *data)
>> n++;
>> }
>>
>> + unsigned max = 0;
>> EXECUTE_IF_SET_IN_BITMAP (data->relevant, 0, j, bi)
>> {
>> struct version_info *info = ver_info (data, j);
>> -
>> if (info->inv_id && info->has_nonlin_use)
>> - n++;
>> + {
>> + tree ssa_name = ssa_name (j);
>> + n = get_regs_used (ssa_name);
>> + if (n >= max)
>> + max = n;
>> + }
>> }
>>
>> - data->regs_used = n;
>> + data->regs_used = max;
>> if (dump_file && (dump_flags & TDF_DETAILS))
>> fprintf (dump_file, " regs_used %d\n", n);
>>
>> --
>> 2.39.3
>>
>>
