solver: remove backjumping by name

It is incorrect optimization causing valid solutions to be skipped.
Any performance it might've gained, should be fixed by reintroduction
of the minimum penalty logic added in previous commit.

2 files changed, 3 insertions, 29 deletions

diff --git a/src/apk_solver_data.h b/src/apk_solver_data.h
index 5921e41..5777325 100644
--- a/src/apk_solver_data.h
+++ b/src/apk_solver_data.h
@@ -63,7 +63,6 @@ struct apk_solver_name_state {
 	unsigned none_excluded : 1;
 	unsigned name_touched : 1;
 	unsigned preferred_chosen : 1;
-	unsigned backjump_enabled : 1;
 };
 
 #endif
diff --git a/src/solver.c b/src/solver.c
index af906d4..d6ac1e1 100644
--- a/src/solver.c
+++ b/src/solver.c
@@ -913,7 +913,6 @@ static solver_result_t push_decision(struct apk_solver_state *ss,
 static int next_branch(struct apk_solver_state *ss)
 {
 	unsigned int backup_until = ss->num_decisions;
-	struct apk_name *backjump_name = NULL;
 
 	while (ss->num_decisions > 0) {
 		struct apk_decision *d = &ss->decisions[ss->num_decisions];
@@ -921,11 +920,6 @@ static int next_branch(struct apk_solver_state *ss)
 
 		undo_decision(ss, d);
 
-		/* If we undoed constraints on the backjump name, we
-		 * cannot backjump on it anymore. */
-		if (backjump_name && !backjump_name->ss.backjump_enabled)
-			backjump_name = NULL;
-
 #ifdef DEBUG_CHECKS
 		ASSERT(cmpscore(&d->saved_score, &ss->score) == 0,
 			"Saved_score "SCORE_FMT" != score "SCORE_FMT,
@@ -936,32 +930,19 @@ static int next_branch(struct apk_solver_state *ss)
 			name->name, d->saved_requirers, name->ss.requirers);
 #endif
 
-		if ((backjump_name == NULL || backjump_name == name) &&
-		    backup_until >= ss->num_decisions &&
+		if (backup_until >= ss->num_decisions &&
 		    d->branching_point == BRANCH_YES) {
 			d->branching_point = BRANCH_NO;
 			d->type = (d->type == DECISION_ASSIGN) ? DECISION_EXCLUDE : DECISION_ASSIGN;
 			return apply_decision(ss, d);
 		} else if (d->branching_point == BRANCH_YES) {
-			if (backup_until < ss->num_decisions)
-				dbg_printf("skipping %s, %d < %d\n",
-					name->name, backup_until, ss->num_decisions);
-			else if (backjump_name != NULL && backjump_name != name)
-				dbg_printf("backjumping to find new assign candidate for %s\n",
-					backjump_name->name);
+			dbg_printf("skipping %s, %d < %d\n",
+				name->name, backup_until, ss->num_decisions);
 		}
 
-		/* Back jump to find assign candidate for this name */
-		if (name->ss.backjump_enabled && backjump_name == NULL)
-			backjump_name = name;
-
 		/* When undoing the initial "exclude none" decision, check if
 		 * we can backjump. */
 		if (d->has_package == 0 && !d->found_solution) {
-			if (backjump_name == name) {
-				d->name->ss.backjump_enabled = 0;
-				backjump_name = NULL;
-			}
 			if (d->backup_until && d->backup_until < backup_until) {
 				backup_until = d->backup_until;
 				/* We can't backtrack over the immediate
@@ -1093,7 +1074,6 @@ static void undo_constraint(struct apk_solver_state *ss, struct apk_dependency *
 				ps0->conflicts--;
 			else
 				ps0->unsatisfied--;
-			pkg0->name->ss.backjump_enabled = 0;
 			dbg_printf(PKG_VER_FMT ": conflicts-- -> %d\n",
 				   PKG_VER_PRINTF(pkg0),
 				   ps0->conflicts);
@@ -1144,7 +1124,6 @@ static int reconsider_name(struct apk_solver_state *ss, struct apk_name *name)
 			return push_decision(ss, name, NULL, DECISION_EXCLUDE, BRANCH_NO, FALSE);
 		}
 
-		name->ss.backjump_enabled = 0;
 		return push_decision(ss, name, NULL, DECISION_EXCLUDE, BRANCH_YES, FALSE);
 	}
 
@@ -1200,7 +1179,6 @@ static int reconsider_name(struct apk_solver_state *ss, struct apk_name *name)
 
 	/* no options left */
 	if (options == 0) {
-		name->ss.backjump_enabled = 1;
 		if (name->ss.none_excluded) {
 			dbg_printf("reconsider_name: %s: no options pruning branch\n",
 				name->name);
@@ -1212,7 +1190,6 @@ static int reconsider_name(struct apk_solver_state *ss, struct apk_name *name)
 	} else if (options == 1 && score_locked && name->ss.none_excluded && name == next_p->pkg->name) {
 		dbg_printf("reconsider_name: %s: only one choice left with known score, locking.\n",
 			name->name);
-		name->ss.backjump_enabled = 1;
 		return push_decision(ss, name, next_p->pkg, DECISION_ASSIGN, BRANCH_NO, FALSE);
 	}
 
@@ -1290,7 +1267,6 @@ static int expand_branch(struct apk_solver_state *ss)
 			primary_decision = DECISION_ASSIGN;
 		else
 			primary_decision = DECISION_EXCLUDE;
-		name->ss.backjump_enabled = 0;
 		return push_decision(ss, name, NULL, primary_decision, BRANCH_YES, FALSE);
 	}
 
@@ -1362,7 +1338,6 @@ static void record_solution(struct apk_solver_state *ss)
 		unsigned short pinning;
 		unsigned int repos;
 
-		name->ss.backjump_enabled = 0;
 		d->found_solution = 1;
 
 		if (pkg == NULL) {