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Cap niter_for_unrolled_loop to upper bound
- From: Richard Sandiford <richard dot sandiford at linaro dot org>
- To: gcc-patches at gcc dot gnu dot org
- Date: Thu, 04 May 2017 07:47:48 +0100
- Subject: Cap niter_for_unrolled_loop to upper bound
- Authentication-results: sourceware.org; auth=none
For the reasons explained in PR77536, niter_for_unrolled_loop assumes 5
iterations in the absence of profiling information, although it doesn't
increase beyond the estimate for the original loop. This left a hole in
which the new estimate could be less than the old one but still greater
than the limit imposed by CEIL (nb_iterations_upper_bound, unroll factor).
Tested on aarch64-linux-gnu and x86_64-linux-gnu. OK to install?
Thanks,
Richard
gcc/
2017-05-04 Richard Sandiford <richard.sandiford@linaro.org>
* tree-ssa-loop-manip.c (niter_for_unrolled_loop): Add commentary
to explain the use of truncating division. Cap the number of
iterations to the maximum given by nb_iterations_upper_bound,
if defined.
gcc/testsuite/
* gcc.dg/vect/vect-profile-1.c: New test.
Index: gcc/tree-ssa-loop-manip.c
===================================================================
--- gcc/tree-ssa-loop-manip.c 2017-05-03 08:46:26.068861808 +0100
+++ gcc/tree-ssa-loop-manip.c 2017-05-04 07:41:56.686034705 +0100
@@ -1104,6 +1104,9 @@ niter_for_unrolled_loop (struct loop *lo
gcc_assert (factor != 0);
bool profile_p = false;
gcov_type est_niter = expected_loop_iterations_unbounded (loop, &profile_p);
+ /* Note that this is really CEIL (est_niter + 1, factor) - 1, where the
+ "+ 1" converts latch iterations to loop iterations and the "- 1"
+ converts back. */
gcov_type new_est_niter = est_niter / factor;
/* Without profile feedback, loops for which we do not know a better estimate
@@ -1120,6 +1123,15 @@ niter_for_unrolled_loop (struct loop *lo
new_est_niter = 5;
}
+ if (loop->any_upper_bound)
+ {
+ /* As above, this is really CEIL (upper_bound + 1, factor) - 1. */
+ widest_int bound = wi::udiv_floor (loop->nb_iterations_upper_bound,
+ factor);
+ if (wi::ltu_p (bound, new_est_niter))
+ new_est_niter = bound.to_uhwi ();
+ }
+
return new_est_niter;
}
Index: gcc/testsuite/gcc.dg/vect/vect-profile-1.c
===================================================================
--- /dev/null 2017-05-04 07:24:39.449302696 +0100
+++ gcc/testsuite/gcc.dg/vect/vect-profile-1.c 2017-05-04 07:41:56.685075916 +0100
@@ -0,0 +1,35 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target vect_int } */
+/* { dg-additional-options "-fdump-tree-vect-details-blocks" } */
+
+/* At least one of these should correspond to a full vector. */
+
+void
+f1 (int *x)
+{
+ for (int j = 0; j < 2; ++j)
+ x[j] += 1;
+}
+
+void
+f2 (int *x)
+{
+ for (int j = 0; j < 4; ++j)
+ x[j] += 1;
+}
+
+void
+f3 (int *x)
+{
+ for (int j = 0; j < 8; ++j)
+ x[j] += 1;
+}
+
+void
+f4 (int *x)
+{
+ for (int j = 0; j < 16; ++j)
+ x[j] += 1;
+}
+
+/* { dg-final { scan-tree-dump {goto <bb [0-9]+>; \[0+.0*%\]} vect } } */