[PATCH] [aarch64] Fix PR94591: GCC generates invalid rev64 insns

[Alex Coplan]

Hello,

This patch fixes PR94591. The problem was the function aarch64_evpc_rev_local()
matching vector permutations that were not reversals. In particular, prior to
this patch, this function matched the identity permutation which led to
generating bogus REV64 insns which were rejected by the assembler.

Testing:
 - New regression test which passes after applying the patch.
 - New test passes on an x64 -> aarch64-none-elf cross.
 - Bootstrap and regtest on aarch64-linux-gnu.

OK to install?

Thanks,
Alex

---

gcc/ChangeLog:

2020-05-19  Alex Coplan  <alex.cop...@arm.com>

        PR target/94591
        * config/aarch64/aarch64.c (aarch64_evpc_rev_local): Don't match
        identity permutation.

gcc/testsuite/ChangeLog:

2020-05-19  Alex Coplan  <alex.cop...@arm.com>

        PR target/94591
        * gcc.c-torture/execute/pr94591.c: New test.

diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
index 70aa2f752b5..79c016f4dc3 100644
--- a/gcc/config/aarch64/aarch64.c
+++ b/gcc/config/aarch64/aarch64.c
@@ -20191,7 +20191,8 @@ aarch64_evpc_rev_local (struct expand_vec_perm_d *d)
 
   if (d->vec_flags == VEC_SVE_PRED
       || !d->one_vector_p
-      || !d->perm[0].is_constant (&diff))
+      || !d->perm[0].is_constant (&diff)
+      || !diff)
     return false;
 
   size = (diff + 1) * GET_MODE_UNIT_SIZE (d->vmode);
diff --git a/gcc/testsuite/gcc.c-torture/execute/pr94591.c b/gcc/testsuite/gcc.c-torture/execute/pr94591.c
new file mode 100644
index 00000000000..42271ad8bce
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/execute/pr94591.c
@@ -0,0 +1,32 @@
+typedef unsigned __attribute__((__vector_size__(8))) V2SI_u;
+typedef int __attribute__((__vector_size__(8))) V2SI_d;
+
+typedef unsigned long __attribute__((__vector_size__(16))) V2DI_u;
+typedef long __attribute__((__vector_size__(16))) V2DI_d;
+
+void id_V2SI(V2SI_d *v)
+{
+  *v = __builtin_shuffle(*v, (V2SI_d)(V2SI_u) { 0, 1 });
+}
+
+void id_V2DI(V2DI_d *v)
+{
+  *v = __builtin_shuffle(*v, (V2DI_d)(V2DI_u) { 0, 1 });
+}
+
+extern void abort(void);
+
+int main(void)
+{
+  V2SI_d si = { 35, 42 };
+  id_V2SI(&si);
+
+  if (si[0] != 35 || si[1] != 42)
+    abort();
+
+  V2DI_d di = { 63, 38 };
+  id_V2DI(&di);
+
+  if (di[0] != 63 || di[1] != 38)
+    abort();
+}