scc

commit 1fabb15195b1f854521b286ff3461cfcfe84ec75
parent 2c0c00b541f14afe82c47e08b6bb2ec76c84d013
Author: Roberto E. Vargas Caballero <k0ga@shike2.com>
Date:   Tue,  7 Jan 2025 17:24:02 +0100

cc2: Apply jump optimizations until no changes

Also, apply removal of not referenced labels in the same path,
because passing again just to removal them is so expensive like
trying all the optimizations.

Diffstat:
M
src/cmd/scc-cc/cc2/cfg.c
 | 
57
++++++++++++++++++++++++++++++++++++---------------------

1 file changed, 36 insertions(+), 21 deletions(-)
diff --git a/src/cmd/scc-cc/cc2/cfg.c b/src/cmd/scc-cc/cc2/cfg.c
@@ -14,6 +14,7 @@ struct cfg {
 };
 
 static struct cfg cfg;
+static int modjmp;
 
 static Node *
 jtarget(Node *np)
@@ -271,14 +272,6 @@ buildcfg(void)
 	PRCFG("cfg");
 }
 
-static Node *
-optlabels(Node *np)
-{
-	if (np->op == ONOP && np->label->refcnt == 0)
-		return NULL;
-	return np;
-}
-
 static int
 negop(int op)
 {
@@ -295,12 +288,26 @@ negop(int op)
 }
 
 static Node *
-optjmps(Node *np)
+skipnop(Node *np, Node *target)
+{
+	for ( ; np->op == ONOP && np != target; np = np->next)
+		;
+	return np;
+}
+
+static Node *
+optjmps_helper(Node *np)
 {
 	Symbol *label;
 	Node *p, *stmt, *next;
 
 	switch (np->op) {
+	case ONOP:
+		if (np->label->refcnt == 0) {
+			modjmp = 1;
+			return NULL;
+		}
+		break;
 	case OBRANCH:
 	branch:
 		label = np->u.sym;
@@ -315,6 +322,7 @@ optjmps(Node *np)
 			label->refcnt--;
 			left->op = negop(left->op);
 			delstmt(next);
+			modjmp = 1;
 			goto branch;
 		}
 		goto chain_jumps;
@@ -323,24 +331,22 @@ optjmps(Node *np)
 		stmt = label->u.stmt;
 
 		/* avoid jump over a set of NOPs */
-		for (p = np->next; p; p = p->next) {
-			if (p == stmt) {
-				label->refcnt--;
-				return NULL;
-			}
-			if (p->op != ONOP)
-				break;
+		p = skipnop(np->next, stmt);
+		if (p == stmt) {
+			label->refcnt--;
+			modjmp = 1;
+			return NULL;
 		}
 
 	chain_jumps:
 		/* avoid chain of jumps to jumps */
-		for (p = stmt; p && p->op == ONOP; p = p->next)
-			;
-		if (p && p != np && p->op == OJMP) {
+		p = skipnop(stmt, NULL);
+		if (p != np && p->op == OJMP) {
 			label->refcnt--;
 			label = p->u.sym;
 			stmt = label->u.stmt;
 			np->u.sym = label;
+			modjmp = 1;
 			goto chain_jumps;
 		}
 	}
@@ -348,11 +354,20 @@ optjmps(Node *np)
 	return np;
 }
 
+static void
+optjmps(void)
+{
+	do {
+		modjmp = 0;
+		apply(optjmps_helper);
+		PRTREE("after_modjmp");
+	} while (modjmp == 1);
+}
+
 void
 gencfg(void)
 {
-	apply(optjmps);
-	apply(optlabels);
+	optjmps();
 	DBG("new cfg");
 	buildcfg();
 	trimcfg();