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loop-unroll.c TLC 2/4
- From: Jan Hubicka <hubicka at ucw dot cz>
- To: gcc-patches at gcc dot gnu dot org
- Date: Sat, 20 Oct 2012 17:53:23 +0200
- Subject: loop-unroll.c TLC 2/4
Hi,
this patch fixes heuristic on decide_unroll_constant_iterations to take into
account the profile: even when the loop is known to have constant loop
iteration bound, it doesn't need to really iterate many times. So use profile
and loop_max to double check that this is the case.
Bootstrapped/regtested x86_64-linux, comitted.
Honza
* loop-unroll.c (decide_unroll_constant_iterations): Don't
perform unrolling for loops with low iterations bounds or estimates.
Index: loop-unroll.c
===================================================================
--- loop-unroll.c (revision 192632)
+++ loop-unroll.c (working copy)
@@ -519,6 +519,7 @@ decide_unroll_constant_iterations (struc
{
unsigned nunroll, nunroll_by_av, best_copies, best_unroll = 0, n_copies, i;
struct niter_desc *desc;
+ double_int iterations;
if (!(flags & UAP_UNROLL))
{
@@ -561,8 +562,14 @@ decide_unroll_constant_iterations (struc
return;
}
- /* Check whether the loop rolls enough to consider. */
- if (desc->niter < 2 * nunroll)
+ /* Check whether the loop rolls enough to consider.
+ Consult also loop bounds and profile; in the case the loop has more
+ than one exit it may well loop less than determined maximal number
+ of iterations. */
+ if (desc->niter < 2 * nunroll
+ || ((estimated_loop_iterations (loop, &iterations)
+ || max_loop_iterations (loop, &iterations))
+ && iterations.ult (double_int::from_shwi (2 * nunroll))))
{
if (dump_file)
fprintf (dump_file, ";; Not unrolling loop, doesn't roll\n");
Index: testsuite/gcc.dg/tree-prof/unroll-1.c
===================================================================
--- testsuite/gcc.dg/tree-prof/unroll-1.c (revision 0)
+++ testsuite/gcc.dg/tree-prof/unroll-1.c (revision 0)
@@ -0,0 +1,24 @@
+/* { dg-options "-O3 -fdump-rtl-loop2_unroll -funroll-loops -fno-peel-loops" } */
+void abort ();
+
+int a[1000];
+int
+__attribute__ ((noinline))
+t()
+{
+ int i;
+ for (i=0;i<1000;i++)
+ if (!a[i])
+ return 1;
+ abort ();
+}
+main()
+{
+ int i;
+ for (i=0;i<1000;i++)
+ t();
+ return 0;
+}
+/* { dg-final-use { scan-rtl-dump "Considering unrolling loop with constant number of iterations" "loop2_unroll" } } */
+/* { dg-final-use { cleanup-rtl-dump "Not unrolling loop, doesn't roll" } } */
+/* { dg-options "-O3 -fdump-rtl-loop2_unroll -funroll-loops -fno-peel-loops" } */