From 5b8a2d225ca3777c7b49421182bb5c1faf99ae64 Mon Sep 17 00:00:00 2001
From: Michael Forney <mforney@mforney.org>
Date: Wed, 3 Apr 2019 12:36:14 -0700
Subject: Revert "Make member access its own expression type"

This reverts commit b3865e402e426387d4cdccdcd249a02d5ba1bc05.

This breaks member address expressions in static initializers. We can
support bit-fields by instead adding a "bit-field" expression that
affects loads and stores to the underlying object.
---
 expr.c                    | 24 ++++++++++++------------
 expr.h                    | 10 +++-------
 qbe.c                     |  3 ---
 tests/struct-return-2.qbe |  9 ++++++---
 4 files changed, 21 insertions(+), 25 deletions(-)

diff --git a/expr.c b/expr.c
index 629ae22..d30669c 100644
--- a/expr.c
+++ b/expr.c
@@ -483,7 +483,9 @@ postfixexpr(struct scope *s, struct expr *r)
 	struct type *t;
 	enum typequal tq;
 	struct param *p;
+	uint64_t offset;
 	enum tokenkind op;
+	bool lvalue;
 
 	if (!r)
 		r = primaryexpr(s);
@@ -564,19 +566,17 @@ postfixexpr(struct scope *s, struct expr *r)
 			next();
 			if (tok.kind != TIDENT)
 				error(&tok.loc, "expected identifier after '->' operator");
-			e = mkexpr(EXPRMEMBER, NULL, 0);
-			e->member.base = r;
-			e->member.offset = 0;
-			e->type = typemember(t, tok.lit, &e->member.offset);
-			if (!e->type)
+			lvalue = op == TARROW || r->unary.base->flags & EXPRFLAG_LVAL;
+			r = exprconvert(r, mkpointertype(&typechar));
+			offset = 0;
+			t = typemember(t, tok.lit, &offset);
+			if (!t)
 				error(&tok.loc, "struct/union has no member named '%s'", tok.lit);
-			if (op == TARROW || r->unary.base->flags & EXPRFLAG_LVAL) {
-				e->type = mkqualifiedtype(e->type, tq);
-				e->flags |= EXPRFLAG_LVAL;
-			} else {
-				e->type = typeunqual(e->type, NULL);
-			}
-			e = decay(e);
+			r = mkbinaryexpr(&tok.loc, TADD, r, mkconstexpr(&typeulong, offset));
+			r = exprconvert(r, mkpointertype(mkqualifiedtype(t, tq)));
+			e = mkunaryexpr(TMUL, r);
+			if (!lvalue)
+				e->flags &= ~EXPRFLAG_LVAL;
 			next();
 			break;
 		case TINC:
diff --git a/expr.h b/expr.h
index 5667839..e660848 100644
--- a/expr.h
+++ b/expr.h
@@ -6,7 +6,7 @@ enum exprkind {
 
 	/* postfix expression */
 	EXPRCALL,
-	EXPRMEMBER,
+	/* member E.M gets transformed to *(typeof(E.M) *)((char *)E + offsetof(typeof(E), M)) */
 	EXPRINCDEC,
 	EXPRCOMPOUND,
 	/* subscript E1[E2] gets transformed to *((E1)+(E2)) */
@@ -49,17 +49,13 @@ struct expr {
 			size_t nargs;
 		} call;
 		struct {
-			struct expr *base;
-			size_t offset;
-		} member;
+			struct init *init;
+		} compound;
 		struct {
 			int op;
 			_Bool post;
 			struct expr *base;
 		} incdec;
-		struct {
-			struct init *init;
-		} compound;
 		struct {
 			int op;
 			struct expr *base;
diff --git a/qbe.c b/qbe.c
index 66cc271..a40540a 100644
--- a/qbe.c
+++ b/qbe.c
@@ -479,8 +479,6 @@ objectaddr(struct func *f, struct expr *e)
 	case EXPRSTRING:
 		d = stringdecl(e);
 		return d->value;
-	case EXPRMEMBER:
-		return funcinst(f, IADD, &iptr, funcexpr(f, e->member.base), mkintconst(&iptr, e->member.offset));
 	case EXPRCOMPOUND:
 		d = mkdecl(DECLOBJECT, e->type, LINKNONE);
 		funcinit(f, d, e->compound.init);
@@ -601,7 +599,6 @@ funcexpr(struct func *f, struct expr *e)
 		if (typeprop(e->type) & PROPINT || e->type->kind == TYPEPOINTER)
 			return mkintconst(e->type->repr, e->constant.i);
 		return mkfltconst(e->type->repr, e->constant.f);
-	case EXPRMEMBER:
 	case EXPRCOMPOUND:
 		l = objectaddr(f, e);
 		return funcload(f, e->type, l);
diff --git a/tests/struct-return-2.qbe b/tests/struct-return-2.qbe
index b1990ec..415ec2f 100644
--- a/tests/struct-return-2.qbe
+++ b/tests/struct-return-2.qbe
@@ -5,7 +5,10 @@ function w $f() {
 @body.2
 	%.1 =:.1 call $g()
 	%.2 =l copy %.1
-	%.3 =l add %.2, 4
-	%.4 =w loadsw %.3
-	ret %.4
+	%.3 =l copy %.2
+	%.4 =l mul 4, 1
+	%.5 =l add %.3, %.4
+	%.6 =l copy %.5
+	%.7 =w loadsw %.6
+	ret %.7
 }
-- 
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