[AArch64] Backport to gcc-7 PR71727 fix -mstrict-align

[Christophe Lyon]

Hi,

I've recently committed a follow-up fix for PR71727 for -mstrict-align
on aarch64 (r253242).
I think it would be appropriate to apply it to gcc-7-branch. The patch
from trunk applies cleanly to gcc-7-branch.

Although the original bug was reported against 4.9.4, 5.3.1, 6.1.0,
Naveen's patch was not backported to these branches, so it's not
appropriate to backport my patch there.

OK?

Thanks,

Christophe

2017-09-20  Christophe Lyon  <christophe.l...@linaro.org>

        PR target/71727
        gcc/
        * config/aarch64/aarch64.c
        (aarch64_builtin_support_vector_misalignment): Always return false
        when misalignment is unknown.

        gcc/testsuite/
        * gcc.target/aarch64/pr71727-2.c: New test.

diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
index 799989a..7cc67ec 100644
--- a/gcc/config/aarch64/aarch64.c
+++ b/gcc/config/aarch64/aarch64.c
@@ -11757,19 +11757,9 @@ aarch64_builtin_support_vector_misalignment 
(machine_mode mode,
       if (optab_handler (movmisalign_optab, mode) == CODE_FOR_nothing)
         return false;
 
+      /* Misalignment factor is unknown at compile time.  */
       if (misalignment == -1)
-       {
-         /* Misalignment factor is unknown at compile time but we know
-            it's word aligned.  */
-         if (aarch64_simd_vector_alignment_reachable (type, is_packed))
-            {
-              int element_size = TREE_INT_CST_LOW (TYPE_SIZE (type));
-
-              if (element_size != 64)
-                return true;
-            }
-         return false;
-       }
+       return false;
     }
   return default_builtin_support_vector_misalignment (mode, type, misalignment,
                                                      is_packed);
diff --git a/gcc/testsuite/gcc.target/aarch64/pr71727-2.c 
b/gcc/testsuite/gcc.target/aarch64/pr71727-2.c
new file mode 100644
index 0000000..2bc803a
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/pr71727-2.c
@@ -0,0 +1,16 @@
+/* { dg-do compile } */
+/* { dg-options "-mstrict-align -O3" } */
+
+unsigned char foo(const unsigned char *buffer, unsigned int length)
+{
+  unsigned char sum;
+  unsigned int  count;
+
+  for (sum = 0, count = 0; count < length; count++) {
+    sum = (unsigned char) (sum + *(buffer + count));
+  }
+
+  return sum;
+}
+
+/* { dg-final { scan-assembler-times "and\tw\[0-9\]+, w\[0-9\]+, 15" 1 } } */