[PATCH] vect: Don't retry if the previous analysis fails

["Kewen.Lin" <linkw@linux.ibm.com>]

Hi,

When working on a cost tweaking patch, I found that a newly
added test case has different dumpings with stage-1 and
bootstrapped gcc.  By looking into it, the apparent reason
is vect_analyze_loop_2 doesn't get slp_done_for_suggested_uf
set expectedly, the following retrying will use the garbage
slp_done_for_suggested_uf instead.  In fact, the setting of
slp_done_for_suggested_uf only happens when the previous
analysis succeeds, for the mentioned test case, its previous
analysis does fail, it's unexpected to use the value of
slp_done_for_suggested_uf any more.

In function vect_analyze_loop_1, we only return success when
res is true, which is the result of 1st analysis.  It means
we never try to vectorize with unroll_vinfo if the previous
analysis fails.  So this patch shouldn't break anything, and
just stop some useless analysis early.

Bootstrapped and regtested on x86_64-redhat-linux,
aarch64-linux-gnu and powerpc64{,le}-linux-gnu.

Is it ok for trunk?

BR,
Kewen
-----
gcc/ChangeLog:

	* tree-vect-loop.cc (vect_analyze_loop_1): Don't retry analysis with
	suggested unroll factor once the previous analysis fails.
---
 gcc/tree-vect-loop.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
index ed0166fedab..905145ae97b 100644
--- a/gcc/tree-vect-loop.cc
+++ b/gcc/tree-vect-loop.cc
@@ -3044,7 +3044,7 @@ vect_analyze_loop_1 (class loop *loop, vec_info_shared *shared,
 		     res ? "succeeded" : " failed",
 		     GET_MODE_NAME (loop_vinfo->vector_mode));

-  if (!main_loop_vinfo && suggested_unroll_factor > 1)
+  if (res && !main_loop_vinfo && suggested_unroll_factor > 1)
     {
       if (dump_enabled_p ())
 	dump_printf_loc (MSG_NOTE, vect_location,
--
2.31.1