vect_recog_divmod_pattern currently bails out if the target has
native support for integer division, but I think in practice
it's always going to be better to open-code it anyway, just as
we usually open-code scalar divisions by constants.
I think the only currently affected target is MIPS MSA, where for:
void
foo (int *x)
{
for (int i = 0; i < 100; ++i)
x[i] /= 2;
}
we previously preferred to use division for powers of 2:
.set noreorder
bnz.w $w1,1f
div_s.w $w0,$w0,$w1
break 7
.set reorder
1:
(or just the div_s.w for -mno-check-zero-division), but after the patch
we open-code them using shifts:
clt_s.w $w1,$w0,$w2
subv.w $w0,$w0,$w1
srai.w $w0,$w0,1
I assume that's better. Matthew, is that right?
MSA doesn't define a high-part pattern, so it still uses a division
instruction for the non-power-of-2 case.
Richard B pointed out that this would disable SLP of division by
different amounts, but I think in practice that's a price worth paying,
since the current cost model can't really tell whether using a general
vector division is better than using open-coded scalar divisions.
The fix would be either to support SLP of mixed open-coded divisions
or to improve the cost model and try SLP again without the patterns.
The patch adds an XFAILed test for this.
Tested on aarch64-linux-gnu (with and without SVE), aarch64_be-elf
and x86_64-linux-gnu. OK to install?
Richard
2018-05-24 Richard Sandiford <[email protected]>
gcc/
* tree-vect-patterns.c (vect_recog_divmod_pattern): Remove check
for division support.
gcc/testsuite/
* gcc.dg/vect/bb-slp-div-1.c: New XFAILed test.
Index: gcc/tree-vect-patterns.c
===================================================================
--- gcc/tree-vect-patterns.c 2018-05-16 12:48:59.115202362 +0100
+++ gcc/tree-vect-patterns.c 2018-05-24 09:18:10.445466941 +0100
@@ -2639,7 +2639,6 @@ vect_recog_divmod_pattern (vec<gimple *>
enum tree_code rhs_code;
stmt_vec_info stmt_vinfo = vinfo_for_stmt (last_stmt);
vec_info *vinfo = stmt_vinfo->vinfo;
- optab optab;
tree q;
int dummy_int, prec;
stmt_vec_info def_stmt_vinfo;
@@ -2674,17 +2673,6 @@ vect_recog_divmod_pattern (vec<gimple *>
if (vectype == NULL_TREE)
return NULL;
- /* If the target can handle vectorized division or modulo natively,
- don't attempt to optimize this. */
- optab = optab_for_tree_code (rhs_code, vectype, optab_default);
- if (optab != unknown_optab)
- {
- machine_mode vec_mode = TYPE_MODE (vectype);
- int icode = (int) optab_handler (optab, vec_mode);
- if (icode != CODE_FOR_nothing)
- return NULL;
- }
-
prec = TYPE_PRECISION (itype);
if (integer_pow2p (oprnd1))
{
Index: gcc/testsuite/gcc.dg/vect/bb-slp-div-1.c
===================================================================
--- /dev/null 2018-04-20 16:19:46.369131350 +0100
+++ gcc/testsuite/gcc.dg/vect/bb-slp-div-1.c 2018-05-24 09:18:10.444466986
+0100
@@ -0,0 +1,19 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-msve-vector-bits=256" { target aarch64_sve } } */
+
+int x[8];
+
+void
+f (void)
+{
+ x[0] /= 2;
+ x[1] /= 3;
+ x[2] /= 4;
+ x[3] /= 5;
+ x[4] /= 6;
+ x[5] /= 7;
+ x[6] /= 8;
+ x[7] /= 9;
+}
+
+/* { dg-final { scan-tree-dump "basic block vectorized" "slp2" { xfail *-*-* }
} } */
