i965/vec4: Don't reswizzle hardware registers

Cc: "11.0 10.6" <mesa-stable@lists.freedesktop.org>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91719
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/mesa/drivers/dri/i965/brw_vec4.cpp

@@ -954,6 +954,14 @@ vec4_instruction::can_reswizzle(int dst_writemask,
    if (mlen > 0)
       return false;
 
+   /* We can't use swizzles on the accumulator and that's really the only
+    * HW_REG we would care to reswizzle so just disallow them all.
+    */
+   for (int i = 0; i < 3; i++) {
+      if (src[i].file == HW_REG)
+         return false;
+   }
+
    return true;
 }