scc

commit 0d701eb4c740238b1b6ac629f4a57004a251e3ab
parent 48b664b106b3aadb1b8b2db95bfb1da0fe7daa0b
Author: Roberto E. Vargas Caballero <k0ga@shike2.com>
Date:   Wed, 11 Jan 2023 13:09:00 +0100

cc1: Collapse field operations combined with &

Using the operator field (.) in the context of an address (&)
operator does not imply to actually use the value in the
struct because it basicaly only implies to add an offset to
te base address of the struct.

Diffstat:
M
src/cmd/cc/cc1/cc1.h
 | 
1
+
M
src/cmd/cc/cc1/code.c
 | 
15
+++++++++++++++
M
src/cmd/cc/cc1/fold.c
 | 
29
++++++++++++++++++++++++++++-

3 files changed, 44 insertions(+), 1 deletion(-)
diff --git a/src/cmd/cc/cc1/cc1.h b/src/cmd/cc/cc1/cc1.h
@@ -482,6 +482,7 @@ extern Node *node(int op, Type *tp, Node *left, Node *rigth);
 extern Node *varnode(Symbol *sym);
 extern Node *constnode(Symbol *sym);
 extern Node *sizeofnode(Type *tp);
+extern Node *offsetnode(Symbol *,  Type *);
 extern void freetree(Node *np);
 extern void icode(void);
 #define BTYPE(np) ((np)->type->op)
diff --git a/src/cmd/cc/cc1/code.c b/src/cmd/cc/cc1/code.c
@@ -1,3 +1,4 @@
+#include <assert.h>
 #include <ctype.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -580,3 +581,17 @@ sizeofnode(Type *tp)
 	DBG("EXPR sizeof %llu", sym->u.u);
 	return constnode(sym);
 }
+
+Node *
+offsetnode(Symbol *field, Type *tp)
+{
+	Symbol *sym;
+
+	assert(field->flags & SFIELD);
+	sym = newsym(NS_IDEN, NULL);
+	sym->type = tp;
+	sym->flags |= SCONSTANT;
+	sym->u.u = field->u.u;
+
+	return constnode(sym);
+}
diff --git a/src/cmd/cc/cc1/fold.c b/src/cmd/cc/cc1/fold.c
@@ -372,7 +372,7 @@ static Node *
 foldunary(Node *np)
 {
 	Node *l = np->left;
-	Node *aux;
+	Node *aux, *aux2;;
 	int op = l->op;
 
 	switch (np->op) {
@@ -397,6 +397,33 @@ foldunary(Node *np)
 			return np;
 		break;
 	case OADDR:
+		/* &(*s).f -> s + offsetof(typeof(*s), f) */
+		if (op == OFIELD && l->left->op == OPTR) {
+			DBG("FOLD collapse '&(*s).f' %d", np->op);
+			aux = offsetnode(l->right->sym, np->type);
+			aux = node(OADD, np->type, l->left->left, aux);
+
+			if (aux->left->flags & NCONST)
+				aux->flags |= NCONST;
+			l->left->left = NULL;
+			freetree(np);
+			return aux;
+		}
+
+		/* &s.f -> &s + offsetof(typeof(s), f) */
+		if (op == OFIELD) {
+			DBG("FOLD collapse '&s.f' %d", np->op);
+			aux = offsetnode(l->right->sym, np->type);
+			aux2 = node(OADDR, np->type, l->left, NULL);
+			aux = node(OADD, np->type, aux2, aux);
+
+			if (l->flags & NCONST)
+				aux->flags |= NCONST;
+			l->left = NULL;
+			freetree(np);
+			return aux;
+		}
+
 		if (op != OPTR)
 			return np;
 		break;