Hi Jeff,
Thanks for the comments.
On 23 June 2018 at 02:06, Jeff Law <l...@redhat.com> wrote:
> On 06/22/2018 03:11 AM, Kugan Vivekanandarajah wrote:
>> When we set niter with maybe_zero, currently final_value_relacement
>> will not happen due to expression_expensive_p not handling. Patch 1
>> adds this.
>>
>> With that we have the following optimized gimple.
>>
>> <bb 2> [local count: 118111601]:
>> if (b_4(D) != 0)
>> goto <bb 3>; [89.00%]
>> else
>> goto <bb 4>; [11.00%]
>>
>> <bb 3> [local count: 105119324]:
>> _2 = (unsigned long) b_4(D);
>> _9 = __builtin_popcountl (_2);
>> c_3 = b_4(D) != 0 ? _9 : 1;
>>
>> <bb 4> [local count: 118111601]:
>> # c_12 = PHI <c_3(3), 0(2)>
>>
>> I assume that 1 in b_4(D) != 0 ? _9 : 1; is OK (?) because when the
>> latch execute zero times for b_4 == 0 means that the body will execute
>> ones.
> ISTM that DOM ought to have simplified the conditional, unless there's
> some other way to get to bb3. We know that b_4 is nonzero and thus c_3
> must have the value _9.
As of now, dom is not optimizing it. With the attached hack, it can be made to.
>
>
>>
>> The issue here is, since we are checking if (b_4(D) != 0) before
>> entering the loop means we don't need to set maybe_zero. Patch 2
>> handles this.
>>
>> With that we have
>> <bb 2> [local count: 118111601]:
>> if (b_4(D) != 0)
>> goto <bb 3>; [89.00%]
>> else
>> goto <bb 4>; [11.00%]
>>
>> <bb 3> [local count: 105119324]:
>> _2 = (unsigned long) b_4(D);
>> _9 = __builtin_popcountl (_2);
>>
>> <bb 4> [local count: 118111601]:
>> # c_12 = PHI <0(2), _9(3)>
>>
>> As advised earlier, patch 3 adds phiopt support to remove this.
> So if DOM or some other pass fixed up the assignment to c_3 I'd hope we
> wouldn't set maybe_zero.
>
> So I'd like to start by first determining if we should have already
> simplified the COND_EXPR in bb3. Do you have a testcase for that?
Sorry, It is hidden in patch 3 (attaching now). You will need patch 1 as well.
Thanks,
Kugan
>
>
> jeff
diff --git a/gcc/tree-ssa-dom.c b/gcc/tree-ssa-dom.c
index a6f176c..77ae7d1b 100644
--- a/gcc/tree-ssa-dom.c
+++ b/gcc/tree-ssa-dom.c
@@ -1991,6 +1991,25 @@ dom_opt_dom_walker::optimize_stmt (basic_block bb,
gimple_stmt_iterator si)
}
}
+ if (gimple_code (stmt) == GIMPLE_ASSIGN
+ && gimple_assign_rhs_code (stmt) == COND_EXPR)
+ {
+ /* If this is a conditional stmt, see if we can optimize the
+ condition. */
+ x_vr_values = evrp_range_analyzer.get_vr_values ();
+ tree exp = gimple_assign_rhs1 (stmt);
+ tree lhs = TREE_OPERAND (exp, 0);
+ tree rhs = TREE_OPERAND (exp, 1);
+ tree val = x_vr_values->vrp_evaluate_conditional (TREE_CODE (exp),
+ lhs, rhs, stmt);
+ if (is_gimple_min_invariant (val))
+ {
+ gimple_assign_set_rhs1 (stmt, val);
+ update_stmt (stmt);
+ }
+ x_vr_values = NULL;
+ }
+
if (gimple_code (stmt) == GIMPLE_COND)
{
tree lhs = gimple_cond_lhs (stmt);
int PopCount (long b) {
int c = 0;
while (b) {
b &= b - 1;
c++;
}
return c;
}
