[PATCH] Fix bootstrap failure in vect_analyze_loop

[David Malcolm <dmalcolm at redhat dot com>]

I ran into this bootstrap failure (with r262092):

../../../src/gcc/tree-vect-loop.c: In function ‘_loop_vec_info* vect_analyze_loop(loop*, loop_vec_info, vec_info_shared*)’:
../../../src/gcc/tree-vect-loop.c:1946:25: error: ‘n_stmts’ may be used uninitialized in this function [-Werror=maybe-uninitialize ]
   ok = vect_analyze_slp (loop_vinfo, *n_stmts);
        ~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
../../../src/gcc/tree-vect-loop.c:2318:12: note: ‘n_stmts’ was declared here
   unsigned n_stmts;
            ^~~~~~~
cc1plus: all warnings being treated as errors

It looks like it's inlining vect_analyze_loop_2 into vect_analyze_loop,
passing &n_stmts in by pointer.

Normally, vect_get_datarefs_in_loop writes:
  *n_stmts = 0;
when
  if (!LOOP_VINFO_DATAREFS (loop_vinfo).exists ())
but not in the "else" path, and then, after lots of complex logic:

  ok = vect_analyze_slp (loop_vinfo, *n_stmts);

it uses the value in vect_analyze_loop_2, passed in via &n_stmts.

So it's not at all clear to me (or the compiler) that the value is
initialized in all paths, and an initialization to zero seems a
reasonable fix.

OK for trunk, assuming the bootstrap succeeds this time?

gcc/ChangeLog:
	* tree-vect-loop.c (vect_analyze_loop): Initialize n_stmts.
---
 gcc/tree-vect-loop.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/gcc/tree-vect-loop.c b/gcc/tree-vect-loop.c
index dacc881..2b3ced2 100644
--- a/gcc/tree-vect-loop.c
+++ b/gcc/tree-vect-loop.c
@@ -2315,7 +2315,7 @@ vect_analyze_loop (struct loop *loop, loop_vec_info orig_loop_vinfo,
       return NULL;
     }
 
-  unsigned n_stmts;
+  unsigned n_stmts = 0;
   poly_uint64 autodetected_vector_size = 0;
   while (1)
     {
-- 
1.8.5.3