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Allow inner-loop reductions with variable-length vectors
- From: Richard Sandiford <richard dot sandiford at arm dot com>
- To: gcc-patches at gcc dot gnu dot org
- Date: Thu, 09 Aug 2018 15:40:41 +0100
- Subject: Allow inner-loop reductions with variable-length vectors
While working on PR 86871, I noticed we were being overly restrictive
when handling variable-length vectors. For:
for (i : ...)
{
res = ...;
for (j : ...)
res op= ...;
a[i] = res;
}
we don't need a reduction operation (although we do for double
reductions like:
res = ...;
for (i : ...)
for (j : ...)
res op= ...;
a[i] = res;
which must still be rejected).
Tested on aarch64-linux-gnu (with and without SVE), aarch64_be-elf and
x86_64-linux-gnu. OK to install?
Richard
2018-08-09 Richard Sandiford <richard.sandiford@arm.com>
gcc/
* tree-vect-loop.c (vectorizable_reduction): Allow inner-loop
reductions for variable-length vectors.
gcc/testsuite/
* gcc.target/aarch64/sve/reduc_8.c: New test.
Index: gcc/tree-vect-loop.c
===================================================================
--- gcc/tree-vect-loop.c 2018-08-01 16:14:50.227052736 +0100
+++ gcc/tree-vect-loop.c 2018-08-09 15:38:35.230258362 +0100
@@ -6711,6 +6711,7 @@ vectorizable_reduction (stmt_vec_info st
}
if (reduction_type != EXTRACT_LAST_REDUCTION
+ && (!nested_cycle || double_reduc)
&& reduc_fn == IFN_LAST
&& !nunits_out.is_constant ())
{
Index: gcc/testsuite/gcc.target/aarch64/sve/reduc_8.c
===================================================================
--- /dev/null 2018-07-26 10:26:13.137955424 +0100
+++ gcc/testsuite/gcc.target/aarch64/sve/reduc_8.c 2018-08-09 15:38:35.230258362 +0100
@@ -0,0 +1,20 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -ftree-vectorize" } */
+
+int
+reduc (int *restrict a, int *restrict b, int *restrict c)
+{
+ for (int i = 0; i < 100; ++i)
+ {
+ int res = 0;
+ for (int j = 0; j < 100; ++j)
+ if (b[i + j] != 0)
+ res = c[i + j];
+ a[i] = res;
+ }
+}
+
+/* { dg-final { scan-assembler-times {\tcmpne\tp[0-9]+\.s, } 1 } } */
+/* We ought to use the CMPNE result for the SEL too. */
+/* { dg-final { scan-assembler-not {\tcmpeq\tp[0-9]+\.s, } { xfail *-*-* } } } */
+/* { dg-final { scan-assembler-times {\tsel\tz[0-9]+\.s, } 1 } } */