This backport contains 1 patch from gcc main stream tree.
The commit id of these patchs list as following in the order of time.

0001-optabs-Don-t-use-scalar-conversions-for-vectors-PR93.patch
b6268016bf46dd63227dcbb73d13c30a3b4b9d2a

diff --git a/gcc/optabs-tree.c b/gcc/optabs-tree.c
index 3d829c27826..badd30bfda8 100644
--- a/gcc/optabs-tree.c
+++ b/gcc/optabs-tree.c
@@ -284,9 +284,14 @@ supportable_convert_operation (enum tree_code code,
   machine_mode m1,m2;
   bool truncp;
 
+  gcc_assert (VECTOR_TYPE_P (vectype_out) && VECTOR_TYPE_P (vectype_in));
+
   m1 = TYPE_MODE (vectype_out);
   m2 = TYPE_MODE (vectype_in);
 
+  if (!VECTOR_MODE_P (m1) || !VECTOR_MODE_P (m2))
+    return false;
+
   /* First check if we can done conversion directly.  */
   if ((code == FIX_TRUNC_EXPR
        && can_fix_p (m1,m2,TYPE_UNSIGNED (vectype_out), &truncp)
diff --git a/gcc/testsuite/gcc.dg/vect/pr93843-1.c b/gcc/testsuite/gcc.dg/vect/pr93843-1.c
new file mode 100644
index 00000000000..23a79ca4c96
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/pr93843-1.c
@@ -0,0 +1,21 @@
+char a;
+struct S { short b, c; } d;
+
+__attribute__((noipa)) void
+foo (int x)
+{
+  if (x != 4)
+    __builtin_abort ();
+}
+
+int
+main ()
+{
+  short *g = &d.c, *h = &d.b;
+  char e = 4 - a;
+  int f;
+  *h = *g = e;
+  for (f = 0; f < 2; f++)
+    foo (d.c);
+  return 0;
+}
diff --git a/gcc/testsuite/gcc.dg/vect/pr93843-2.c b/gcc/testsuite/gcc.dg/vect/pr93843-2.c
new file mode 100644
index 00000000000..5fae3e5be17
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/pr93843-2.c
@@ -0,0 +1,11 @@
+char in[2] = {2, 2};
+short out[2] = {};
+
+int
+main()
+{
+  for (int i = 0; i < 2; ++i)
+    out[i] = in[i];
+  asm("":::"memory");
+  if (out[0] != 2) __builtin_abort();
+}