agx: fix UB in cursor comparison

padding here is implementation-defined, do the cleaner thing. fixes invalid IR
generated with gcc but not clang.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reported-by: Janne Grunau <janne-fdr@jannau.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/29179>

src/asahi/compiler/agx_compile.c

@@ -1082,7 +1082,7 @@ agx_emit_export(agx_builder *b, unsigned base, nir_src src)
       agx_export(&b_, chan, base + (c * stride));
    }
 
-   if (memcmp(&b->cursor, &after_cursor, sizeof(agx_cursor)) == 0) {
+   if (agx_cursors_equal(b->cursor, after_cursor)) {
       b->cursor = agx_after_block_logical(b->cursor.block);
    }
 

src/asahi/compiler/agx_compiler.h

@@ -801,6 +801,18 @@ typedef struct {
    };
 } agx_cursor;
 
+static inline bool
+agx_cursors_equal(agx_cursor a, agx_cursor b)
+{
+   if (a.option != b.option)
+      return false;
+
+   if (a.option == agx_cursor_after_block)
+      return a.block == b.block;
+   else
+      return a.instr == b.instr;
+}
+
 static inline agx_cursor
 agx_after_block(agx_block *block)
 {