Sort maps keys in the loader

The map instructions require that the keys in the instructions
are sorted (for flatmaps). But that is an implementation detail
that should not exposed outside of the BEAM virtual machine.
Therefore, make the sorting of the keys the responsibility of
the loader and not the compiler.

Also note that the sort order for maps with numeric keys or keys
with numeric components has changed in OTP 18. That means that
code compiled for OTP 17 that operated on maps with map keys
might not work in OTP 18 without the sorting in the loader
(although it is unlikely to be an issue in practice).

1 files changed, 80 insertions, 0 deletions

diff --git a/erts/emulator/beam/beam_load.c b/erts/emulator/beam/beam_load.c
index 18e1e312ad..1a6c6c16ad 100644
--- a/erts/emulator/beam/beam_load.c
+++ b/erts/emulator/beam/beam_load.c
@@ -4082,6 +4082,86 @@ is_empty_map(LoaderState* stp, GenOpArg Lit)
 }
 
 /*
+ * Pseudo predicate map_key_sort that will sort the Rest operand for
+ * map instructions as a side effect.
+ */
+
+typedef struct SortGenOpArg {
+    Eterm term;			/* Term to use for comparing  */
+    GenOpArg arg;		/* Original data */
+} SortGenOpArg;
+
+static int
+genopargtermcompare(SortGenOpArg* a, SortGenOpArg* b)
+{
+    return CMP_TERM(a->term, b->term);
+}
+
+static int
+map_key_sort(LoaderState* stp, GenOpArg Size, GenOpArg* Rest)
+{
+    SortGenOpArg* t;
+    unsigned size = Size.val;
+    unsigned i;
+
+    if (size == 2) {
+	return 1;		/* Already sorted. */
+    }
+
+
+    t = (SortGenOpArg *) erts_alloc(ERTS_ALC_T_TMP, size*sizeof(SortGenOpArg));
+
+    /*
+     * Copy original data and sort keys to a temporary array.
+     */
+    for (i = 0; i < size; i += 2) {
+	t[i].arg = Rest[i];
+	switch (Rest[i].type) {
+	case TAG_a:
+	    t[i].term = Rest[i].val;
+	    ASSERT(is_atom(t[i].term));
+	    break;
+	case TAG_i:
+	    t[i].term = make_small(Rest[i].val);
+	    break;
+	case TAG_n:
+	    t[i].term = NIL;
+	    break;
+	case TAG_q:
+	    t[i].term = stp->literals[Rest[i].val].term;
+	    break;
+	default:
+	    /*
+	     * Not a literal key. Not allowed. Only a single
+	     * variable key is allowed in each map instruction.
+	     */
+	    erts_free(ERTS_ALC_T_TMP, (void *) t);
+	    return 0;
+	}
+#ifdef DEBUG
+	t[i+1].term = THE_NON_VALUE;
+#endif
+	t[i+1].arg = Rest[i+1];
+    }
+
+    /*
+     * Sort the temporary array.
+     */
+    qsort((void *) t, size / 2, 2 * sizeof(SortGenOpArg),
+	  (int (*)(const void *, const void *)) genopargtermcompare);
+
+    /*
+     * Copy back the sorted, original data.
+     */
+    for (i = 0; i < size; i++) {
+	Rest[i] = t[i].arg;
+    }
+
+    erts_free(ERTS_ALC_T_TMP, (void *) t);
+    return 1;
+}
+
+/*
  * Replace a get_map_elements with one key to an instruction with one
  * element
  */