diff --git a/src/mesa/drivers/dri/r300/compiler/radeon_compiler_util.c b/src/mesa/drivers/dri/r300/compiler/radeon_compiler_util.c
index 15ec441..9bab28f 100644
--- a/src/mesa/drivers/dri/r300/compiler/radeon_compiler_util.c
+++ b/src/mesa/drivers/dri/r300/compiler/radeon_compiler_util.c
@@ -206,6 +206,10 @@ struct can_use_presub_data {
 	unsigned int AlphaCount;
 };
 
+/**
+ * This callback function counts the number of sources in inst that are
+ * different from the sources in can_use_presub_data->RemoveSrcs.
+ */
 static void can_use_presub_read_cb(
 	void * userdata,
 	struct rc_instruction * inst,
@@ -221,6 +225,8 @@ static void can_use_presub_read_cb(
 		return;
 
 	for(i = 0; i < 3; i++) {
+		fprintf(stderr, "Remove %u file=%u index=%u\n",
+			i, d->RemoveSrcs[i].File, d->RemoveSrcs[i].Index);
 		if (d->RemoveSrcs[i].File == file
 		    && d->RemoveSrcs[i].Index == index) {
 			src_type &=
@@ -233,6 +239,9 @@ static void can_use_presub_read_cb(
 
 	if (src_type & RC_SOURCE_ALPHA)
 		d->AlphaCount++;
+
+	fprintf(stderr, "file=%u index=%u src_type=%u RGB=%u Alpha=%u\n",
+		file, index, src_type, d->RGBCount, d->AlphaCount);
 }
 
 unsigned int rc_inst_can_use_presub(