http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52091
Ira Rosen <irar at il dot ibm.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |irar at il dot ibm.com
--- Comment #5 from Ira Rosen <irar at il dot ibm.com> 2012-02-02 13:22:53 UTC
---
(In reply to comment #4)
I think that the problem here is that
D.2030_19 = prephitmp.17_21 & 65535
is falsely initialized as reduction, while it isn't a reduction. The mistake
occurs because its def_stmt,
prephitmp.17_21 = PHI <d.3_44(7), pretmp.16_28(2)> ,
is a phi node marked as double reduction:
<bb 3>:
# f.6_36 = PHI <f.7_13(7), 0(2)>
# prephitmp.17_21 = PHI <d.3_44(7), pretmp.16_28(2)> - double reduction phi
...
D.2030_19 = prephitmp.17_21 & 65535; - not a reduction stmt
...
<bb 4>:
# b.4_41 = PHI <b.5_11(5), 0(3)>
...
d.3_9 = d_lsm.23_31 & 1;
...
<bb 6>:
# d.3_44 = PHI <d.3_9(4)> - double reduction stmt
I think we should fail to vectorize D.2030_19 = prephitmp.17_21 & 65535, or any
other non-phi/not vect_double_reduction_def stmt with a double reduction phi as
a def_stmt.
We can either check this in every vectorizable_* for every operand, like this:
Index: tree-vect-stmts.c
===================================================================
--- tree-vect-stmts.c (revision 183125)
+++ tree-vect-stmts.c (working copy)
@@ -3326,7 +3326,8 @@ vectorizable_operation (gimple stmt, gimple_stmt_i
op0 = gimple_assign_rhs1 (stmt);
if (!vect_is_simple_use_1 (op0, loop_vinfo, bb_vinfo,
- &def_stmt, &def, &dt[0], &vectype))
+ &def_stmt, &def, &dt[0], &vectype)
+ || dt[0] == vect_double_reduction_def)
{
if (vect_print_dump_info (REPORT_DETAILS))
fprintf (vect_dump, "use not simple.");
or pass stmt or stmt_info to vect_is_simple_use and check it there.
> OT, it is strange that we are creating a reduction for a loop which loops
> exactly as many times as there are units in the vector, that doesn't seem to
> be
> profitable.
>
Right, but doesn't cost model catch this?
