[Bug target/65369] [5 Regression] nettle test failure on powerpc64le-linux-gnu when built with -O3

["jakub at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65369

--- Comment #26 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
So, on my version of the testcase with r210843 -O3 -mcpu=power8 there are like
49
32 bit load in host endianness found at: _105 = MEM[(const unsigned char
*)load_src_25];
occurrences, so I've added a quick hack (should have used dbg counters
parhaps), and
with BSWAPCNT=16 it works fine, with BSWAPCNT=17 it fails.
In the *.optimized dump, I've noticed that this single load matters for
vectorization in md4_update function, with BSWAPCNT=16 a chunk of code isn't
vectorized, with BSWAPCNT=17 it is.

--- tree-ssa-math-opts.c.xx    2015-03-12 17:44:13.000000000 +0100
+++ tree-ssa-math-opts.c    2015-03-12 18:52:49.280605232 +0100
@@ -2132,6 +2132,17 @@ bswap_replace (gimple stmt, gimple_stmt_
       gimple addr_stmt, load_stmt;
       unsigned align;

+static int cntx = -1;
+if (cntx == -1)
+{
+if (getenv ("BSWAPCNT"))
+cntx = atoi (getenv ("BSWAPCNT"));
+else
+cntx = 0x7fffffff;
+}
+if (cntx == 0)
+return false;
+cntx--;
       align = get_object_alignment (src);
       if (bswap && SLOW_UNALIGNED_ACCESS (TYPE_MODE (load_type), align))
     return false;

So very well this might just trigger a latent bug in the vectorizer or powerpc
backend.