Rework value type analysis and remove slice coerce

src/compiler.bbb

@@ -1,4 +1,5 @@
 [extern] memcmp = fn [cc(c)] (a: &u8, b: &u8, byte_count: u64) s32;
+[extern] memcpy = fn [cc(c)] (destination: &u8, source: &u8, byte_count: u64) &u8;
 [extern] exit = fn [cc(c)] (exit_code: s32) noreturn;
 
 assert = fn (ok: u1) void
@@ -257,6 +258,26 @@ arena_allocate_bytes = fn (arena: &Arena, size: u64, alignment: u64) &u8
 
 arena_join_string = fn (arena: &Arena, pieces: [][]u8) []u8
 {
+    >size: u64 = 0;
+
+    for (piece: pieces)
+    {
+        size += pieces.length;
+    }
+
+    >pointer = arena_allocate_bytes(arena, size + 1, 1);
+    >i: u64 = 0;
+
+    for (piece: pieces)
+    {
+        memcpy(pointer + i, piece.pointer, piece.length);
+        i += piece.length;
+    }
+
+    assert(i == size);
+    pointer[i] = 0;
+
+    return pointer[0..size];
 }
 
 GlobalState = struct

src/main.zig

@@ -317,4 +317,5 @@ const names = &[_][]const u8{
     "shortcircuiting_if",
     "field_access_left_assign",
     "for_each",
+    "pointer_decay",
 };

tests/basic_slice.bbb

@@ -17,6 +17,6 @@ slice_receiver = fn (slice: []u8) void
 [export] main = fn [cc(c)] () s32
 {
     >a: [_]u8 = [0, 1, 2];
-    slice_receiver(&a);
+    slice_receiver(a[..]);
     return 0;
 }

tests/pointer_decay.bbb

@@ -0,0 +1,8 @@
+[export] main = fn [cc(c)] () s32
+{
+    >array: [_]s32 = [1, 3, 5];
+    >pointer: &s32 = &array[0];
+    >index: u64 = 0;
+    pointer[index] = 0;
+    return pointer[index];
+}