r300: fix variables detection for paired ALU and TEX instructions in different branches

TEX instrutions can't write xyz and w to separate registers so we
need to create variables from them first, otherwise we can create
two variables from ALU writing the same register xyz and w in other
branch (this usually works when TEX is not present as the xyz and
w can read/write from different registers).

This fixes regalloc because the variables are later used as a
graph nodes.

The variable order should not matter but it slightly does (leading
to approx 0.3% shader-db temps increase as compared to previous
state), so just sort the variables list afterwards to be as close
to the previous behavior as possible and prevent the regression.

CC: mesa-stable
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/6936
Signed-off-by: Pavel Ondračka <pavel.ondracka@gmail.com>
Reviewed-by: Filip Gawin <filip@gawin.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17987>
(cherry picked from commit 88fd397c74)

.pick_status.json

@@ -895,7 +895,7 @@
         "description": "r300: fix variables detection for paired ALU and TEX instructions in different branches",
         "nominated": true,
         "nomination_type": 0,
-        "resolution": 0,
+        "resolution": 1,
         "main_sha": null,
         "because_sha": null
     },

src/gallium/drivers/r300/compiler/radeon_variable.c

@@ -26,6 +26,7 @@
  */
 
 #include <stdio.h>
+#include <stdlib.h>
 #include "radeon_variable.h"
 
 #include "memory_pool.h"
@@ -325,6 +326,31 @@ static void get_variable_pair_helper(
 	get_variable_helper(variable_list, new_var);
 }
 
+/**
+ * Compare function for sorting variable pointers by the lowest instruction
+ * IP from it and its friends.
+ */
+static int cmpfunc_variable_by_ip (const void * a, const void * b) {
+	struct rc_variable * var_a = *(struct rc_variable **)a;
+	struct rc_variable * var_b = *(struct rc_variable **)b;
+	unsigned int min_ip_a = var_a->Inst->IP;
+	unsigned int min_ip_b = var_b->Inst->IP;
+
+	/* Find the minimal IP of a variable and its friends */
+	while (var_a->Friend) {
+		var_a = var_a->Friend;
+		if (var_a->Inst->IP < min_ip_a)
+			min_ip_a = var_a->Inst->IP;
+	}
+	while (var_b->Friend) {
+		var_b = var_b->Friend;
+		if (var_b->Inst->IP < min_ip_b)
+			min_ip_b = var_b->Inst->IP;
+	}
+
+	return (int)min_ip_a - (int)min_ip_b;
+}
+
 /**
  * Generate a list of variables used by the shader program.  Each instruction
  * that writes to a register is considered a variable.  The struct rc_variable
@@ -337,14 +363,42 @@ struct rc_list * rc_get_variables(struct radeon_compiler * c)
 	struct rc_instruction * inst;
 	struct rc_list * variable_list = NULL;
 
+	/* We search for the variables in two loops in order to get it right in
+	 * the following specific case
+	 *
+	 * IF aluresult.x___;
+	 *   ...
+	 *   MAD temp[0].xyz, src0.000, src0.111, src0.000
+	 *   MAD temp[0].w, src0.0, src0.1, src0.0
+	 * ELSE;
+	 *   ...
+	 *   TXB temp[0], temp[1].xy_w, 2D[0] SEM_WAIT SEM_ACQUIRE;
+	 * ENDIF;
+	 * src0.xyz = input[0], src0.w = input[0], src1.xyz = temp[0], src1.w = temp[0] SEM_WAIT
+	 * MAD temp[1].xyz, src0.xyz, src1.xyz, src0.000
+	 * MAD temp[1].w, src0.w, src1.w, src0.0
+	 *
+	 * If we go just in one loop, we will first create two variables for the
+	 * temp[0].xyz and temp[0].w. This happens because they don't share a reader
+	 * as the src1.xyz and src1.w of the instruction where the value is used are
+	 * in theory independent. They are not because the same register is written
+	 * also by the texture instruction in the other branch and TEX can't write xyz
+	 * and w separatelly.
+	 *
+	 * Therefore first search for RC_INSTRUCTION_NORMAL to create variables from
+	 * the texture instruction and than the pair instructions will be properly
+	 * marked as friends. So we will end with only one variable here as we should.
+	 *
+	 * This doesn't matter before the pair translation, because everything is
+	 * RC_INSTRUCTION_NORMAL.
+	 */
 	for (inst = c->Program.Instructions.Next;
 					inst != &c->Program.Instructions;
 					inst = inst->Next) {
-		struct rc_reader_data reader_data;
-		struct rc_variable * new_var;
-		memset(&reader_data, 0, sizeof(reader_data));
-
 		if (inst->Type == RC_INSTRUCTION_NORMAL) {
+			struct rc_reader_data reader_data;
+			struct rc_variable * new_var;
+			memset(&reader_data, 0, sizeof(reader_data));
 			rc_get_readers(c, inst, &reader_data, NULL, NULL, NULL);
 			if (reader_data.ReaderCount == 0) {
 				continue;
@@ -353,7 +407,15 @@ struct rc_list * rc_get_variables(struct radeon_compiler * c)
 				inst->U.I.DstReg.Index,
 				inst->U.I.DstReg.WriteMask, &reader_data);
 			get_variable_helper(&variable_list, new_var);
-		} else {
+		}
+	}
+
+	bool needs_sorting = false;
+	for (inst = c->Program.Instructions.Next;
+					inst != &c->Program.Instructions;
+					inst = inst->Next) {
+		if (inst->Type != RC_INSTRUCTION_NORMAL) {
+			needs_sorting = true;
 			get_variable_pair_helper(&variable_list, c, inst,
 							&inst->U.P.RGB);
 			get_variable_pair_helper(&variable_list, c, inst,
@@ -361,6 +423,25 @@ struct rc_list * rc_get_variables(struct radeon_compiler * c)
 		}
 	}
 
+	if (variable_list && needs_sorting) {
+		unsigned int count = rc_list_count(variable_list);
+		struct rc_variable **variables = memory_pool_malloc(&c->Pool,
+				sizeof(struct rc_variable *) * count);
+
+		struct rc_list * current = variable_list;
+		for(unsigned int i = 0; current; i++, current = current->Next) {
+			struct rc_variable * var = current->Item;
+			variables[i] = var;
+		}
+
+		qsort(variables, count, sizeof(struct rc_variable *), cmpfunc_variable_by_ip);
+
+		current = variable_list;
+		for(unsigned int i = 0; current; i++, current = current->Next) {
+			current->Item = variables[i];
+		}
+	}
+
 	return variable_list;
 }