diff --git a/gcc/testsuite/gcc.dg/torture/pr99954.c b/gcc/testsuite/gcc.dg/torture/pr99954.c
new file mode 100644
index 00000000000..7d447035912
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr99954.c
@@ -0,0 +1,30 @@
+/* { dg-do run } */
+
+#include <assert.h>
+
+#define CONTAINER_KIND union
+
+typedef CONTAINER_KIND container { int value; } container;
+
+void move(container* end, container* start) {
+    container* p;
+    for (p = end; p > start; p--) {
+	(p)->value = (p-1)->value;
+    }
+}
+
+#define N 100
+
+int main(int argc, char* argv[]) {
+    container vals[N];
+    int i;
+    for (i=0; i<N; i++) {
+        vals[i].value = argc + i;
+    }
+    move(&vals[N-1], &vals[0]);
+    assert(vals[0].value == argc + 0);
+    for (i=1; i<N; i++) {
+        assert(vals[i].value == argc + i - 1);
+    }
+    return 0;
+}
diff --git a/gcc/tree-loop-distribution.c b/gcc/tree-loop-distribution.c
index 583bb062b76..8b91a30d1c6 100644
--- a/gcc/tree-loop-distribution.c
+++ b/gcc/tree-loop-distribution.c
@@ -115,6 +115,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "tree-vectorizer.h"
 #include "tree-eh.h"
 #include "gimple-fold.h"
+#include "tree-affine.h"
 
 
 #define MAX_DATAREFS_NUM \
@@ -1212,6 +1213,18 @@ generate_memcpy_builtin (class loop *loop, partition *partition)
     kind = BUILT_IN_MEMCPY;
   else
     kind = BUILT_IN_MEMMOVE;
+  /* Try harder if we're copying a constant size.  */
+  if (kind == BUILT_IN_MEMMOVE && poly_int_tree_p (nb_bytes))
+    {
+      aff_tree asrc, adest;
+      tree_to_aff_combination (src, ptr_type_node, &asrc);
+      tree_to_aff_combination (dest, ptr_type_node, &adest);
+      aff_combination_scale (&adest, -1);
+      aff_combination_add (&asrc, &adest);
+      if (aff_comb_cannot_overlap_p (&asrc, wi::to_poly_widest (nb_bytes),
+				     wi::to_poly_widest (nb_bytes)))
+	kind = BUILT_IN_MEMCPY;
+    }
 
   dest = force_gimple_operand_gsi (&gsi, dest, true, NULL_TREE,
 				   false, GSI_CONTINUE_LINKING);
@@ -1759,11 +1772,11 @@ loop_distribution::classify_builtin_ldst (loop_p loop, struct graph *rdg,
   /* Now check that if there is a dependence.  */
   ddr_p ddr = get_data_dependence (rdg, src_dr, dst_dr);
 
-  /* Classify as memcpy if no dependence between load and store.  */
+  /* Classify as memmove if no dependence between load and store.  */
   if (DDR_ARE_DEPENDENT (ddr) == chrec_known)
     {
       partition->builtin = alloc_builtin (dst_dr, src_dr, base, src_base, size);
-      partition->kind = PKIND_MEMCPY;
+      partition->kind = PKIND_MEMMOVE;
       return;
     }