Hi!
The problem on this testcase is that ldist pass changes some GIMPLE_CONDs
into 0 != 0 or similar, but the pass doesn't perform any cleanups, then
ifcvt is run and does completely useless work of duplicating dead loops
and guarding them with LOOP_VECTORIZED ifns, and then during the ifcvt
cfg cleanup the dead loops are optimized away, but nothing removes the
corresponding LOOP_VECTORIZED ifns. While perhaps we'll need to hook into
the loop removal and remove the dead ifns or remove the dead ifns during
vectorizer pass using a more expensive way at some point (e.g. by scanning
all bb's last insn for GIMPLE_COND checking LOOP_VECTORIZED) at some point,
in this case it seems to me clearly preferrable to let the ldist pass clean
up after itself, so that we don't do useless work in ifcvt from the
beginning.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2017-12-30 Jakub Jelinek <ja...@redhat.com>
PR tree-optimization/83581
* tree-loop-distribution.c (pass_loop_distribution::execute): Return
TODO_cleanup_cfg if any changes have been made.
* gcc.dg/pr83581.c: New test.
--- gcc/tree-loop-distribution.c.jj 2017-12-21 09:43:17.486071696 +0100
+++ gcc/tree-loop-distribution.c 2017-12-30 16:54:08.106143319 +0100
@@ -3103,7 +3103,7 @@ pass_loop_distribution::execute (functio
checking_verify_loop_structure ();
- return 0;
+ return changed ? TODO_cleanup_cfg : 0;
}
} // anon namespace
--- gcc/testsuite/gcc.dg/pr83581.c.jj 2017-12-30 16:55:35.950164947 +0100
+++ gcc/testsuite/gcc.dg/pr83581.c 2017-12-30 16:55:17.520160406 +0100
@@ -0,0 +1,21 @@
+/* PR tree-optimization/83581 */
+/* { dg-do compile } */
+/* { dg-options "-O3 -fno-tree-copy-prop -fno-tree-loop-im" } */
+
+int a, b, c;
+
+int
+foo (int x)
+{
+ int *d = &x;
+ while (a < 1)
+ {
+ for (b = 0; b < 2; ++b)
+ {
+ *d += !!x + 1;
+ d = &c;
+ }
+ ++a;
+ }
+ return *d;
+}
Jakub
