From 199b3e82d9044394029f33ed6937b8677dc4b5be Mon Sep 17 00:00:00 2001
From: Bill Currie <bill@taniwha.org>
Date: Wed, 1 Apr 2020 16:05:26 +0900
Subject: [PATCH] [qfcc] Add killer node to replacement node's edges

When an operand refers to a killed node, it needs to be evaluated AFTER
the killing node is evaluated. This fixes the double-alias bug.
---
 tools/qfcc/include/dags.h |  2 +-
 tools/qfcc/source/dags.c  | 27 ++++++++++++++++++---------
 2 files changed, 19 insertions(+), 10 deletions(-)

diff --git a/tools/qfcc/include/dags.h b/tools/qfcc/include/dags.h
index c83c029f6..534e58511 100644
--- a/tools/qfcc/include/dags.h
+++ b/tools/qfcc/include/dags.h
@@ -59,7 +59,7 @@ typedef struct dagnode_s {
 	int         topo;			///< topological sort order
 	struct set_s *parents;		///< empty if root node
 	int         cost;			///< cost of this node in temp vars
-	unsigned    killed:1;		///< node is unavailable for cse
+	struct dagnode_s *killed;	///< node is unavailable for cse (by node)
 	st_type_t   type;			///< type of node (st_none = leaf)
 	daglabel_t *label;			///< ident/const if leaf node, or operator
 	struct type_s *tl;
diff --git a/tools/qfcc/source/dags.c b/tools/qfcc/source/dags.c
index 83c30b8b7..a2d29c371 100644
--- a/tools/qfcc/source/dags.c
+++ b/tools/qfcc/source/dags.c
@@ -239,8 +239,6 @@ dag_node (operand_t *op)
 		if (op->o.label->daglabel)
 			node = op->o.label->daglabel->dagnode;
 	}
-	if (node && node->killed)
-		node = 0;
 	return node;
 }
 
@@ -266,8 +264,19 @@ dag_make_children (dag_t *dag, statement_t *s,
 
 	flow_analyze_statement (s, 0, 0, 0, operands);
 	for (i = 0; i < 3; i++) {
-		if (!(children[i] = dag_node (operands[i + 1])))
-			children[i] = leaf_node (dag, operands[i + 1], s->expr);
+		dagnode_t  *node = dag_node (operands[i + 1]);
+		dagnode_t  *killer = 0;
+		if (node && node->killed) {
+			killer = node->killed;
+			node = 0;
+		}
+		if (!node) {
+			node = leaf_node (dag, operands[i + 1], s->expr);
+		}
+		if (killer) {
+			set_add (node->edges, killer->number);
+		}
+		children[i] = node;
 	}
 }
 
@@ -473,7 +482,7 @@ static int
 dag_tempop_kill_aliases_visit (tempop_t *tempop, void *_l)
 {
 	daglabel_t *l = (daglabel_t *) _l;
-	dagnode_t  *node = l->dagnode;;
+	dagnode_t  *node = l->dagnode;
 	daglabel_t *label;
 
 	if (tempop == &l->op->o.tempop)
@@ -482,7 +491,7 @@ dag_tempop_kill_aliases_visit (tempop_t *tempop, void *_l)
 	if (label && label->dagnode) {
 		set_add (node->edges, label->dagnode->number);
 		set_remove (node->edges, node->number);
-		label->dagnode->killed = 1;
+		label->dagnode->killed = node;
 	}
 	return 0;
 }
@@ -500,7 +509,7 @@ dag_def_kill_aliases_visit (def_t *def, void *_l)
 	if (label && label->dagnode) {
 		set_add (node->edges, label->dagnode->number);
 		set_remove (node->edges, node->number);
-		label->dagnode->killed = 1;
+		label->dagnode->killed = node;
 	}
 	return 0;
 }
@@ -584,7 +593,7 @@ dagnode_attach_label (dagnode_t *n, daglabel_t *l)
 		// if the node is a leaf, then kill its value so no attempt is made
 		// to reuse it.
 		if (l->dagnode->type == st_none) {
-			l->dagnode->killed = 1;
+			l->dagnode->killed = n;
 		}
 		dagnode_t  *node = l->dagnode;
 		set_union (n->edges, node->parents);
@@ -707,7 +716,7 @@ dag_kill_nodes (dag_t *dag, dagnode_t *n)
 			// operations.
 			continue;
 		}
-		node->killed = 1;
+		node->killed = n;
 	}
 	n->killed = 0;
 }