intel/compiler: do not copy-propagate strided regions to ddx/ddy arguments

The implementation of these opcodes in the generator assumes that their
arguments are packed, and it generates register regions based on that
assumption.

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>

src/intel/compiler/brw_fs_copy_propagation.cpp

@@ -361,6 +361,20 @@ can_take_stride(fs_inst *inst, unsigned arg, unsigned stride,
    return true;
 }
 
+static bool
+instruction_requires_packed_data(fs_inst *inst)
+{
+   switch (inst->opcode) {
+   case FS_OPCODE_DDX_FINE:
+   case FS_OPCODE_DDX_COARSE:
+   case FS_OPCODE_DDY_FINE:
+   case FS_OPCODE_DDY_COARSE:
+      return true;
+   default:
+      return false;
+   }
+}
+
 bool
 fs_visitor::try_copy_propagate(fs_inst *inst, int arg, acp_entry *entry)
 {
@@ -407,6 +421,13 @@ fs_visitor::try_copy_propagate(fs_inst *inst, int arg, acp_entry *entry)
        inst->opcode == SHADER_OPCODE_GEN4_SCRATCH_WRITE)
       return false;
 
+   /* Some instructions implemented in the generator backend, such as
+    * derivatives, assume that their operands are packed so we can't
+    * generally propagate strided regions to them.
+    */
+   if (instruction_requires_packed_data(inst) && entry->src.stride > 1)
+      return false;
+
    /* Bail if the result of composing both strides would exceed the
     * hardware limit.
     */