Handle unary minus specially instead of 0 - x

This is necessary to fix unary negation of floating-point 0 (also
depends on a pending qbe patch).

5 files changed, 41 insertions, 11 deletions

diff --git a/eval.c b/eval.c
index 70febb1..908ce8d 100644
--- a/eval.c
+++ b/eval.c
@@ -27,6 +27,21 @@ cast(struct expr *expr)
 }
 
 static void
+unary(struct expr *expr, enum tokenkind op, struct expr *l)
+{
+	expr->kind = EXPRCONST;
+	if (l->type->prop & PROPFLOAT)
+		op |= F;
+	switch (op) {
+	case TSUB:      expr->u.constant.u = -l->u.constant.u; break;
+	case TSUB|F:    expr->u.constant.f = -l->u.constant.f; break;
+	default:
+		fatal("internal error; unknown unary expression");
+	}
+	cast(expr);
+}
+
+static void
 binary(struct expr *expr, enum tokenkind op, struct expr *l, struct expr *r)
 {
 	expr->kind = EXPRCONST;
@@ -111,19 +126,28 @@ eval(struct expr *expr, enum evalkind kind)
 		break;
 	case EXPRUNARY:
 		l = eval(expr->base, kind);
-		if (expr->op != TBAND)
+		switch (expr->op) {
+		case TBAND:
+			switch (l->kind) {
+			case EXPRUNARY:
+				if (l->op == TMUL)
+					expr = eval(l->base, kind);
+				break;
+			case EXPRSTRING:
+				if (kind != EVALINIT)
+					break;
+				l->u.ident.decl = stringdecl(l);
+				l->kind = EXPRIDENT;
+				expr->base = l;
+				break;
+			}
 			break;
-		switch (l->kind) {
-		case EXPRUNARY:
-			if (l->op == TMUL)
-				expr = eval(l->base, kind);
+		case TMUL:
 			break;
-		case EXPRSTRING:
-			if (kind != EVALINIT)
+		default:
+			if (l->kind != EXPRCONST)
 				break;
-			l->u.ident.decl = stringdecl(l);
-			l->kind = EXPRIDENT;
-			expr->base = l;
+			unary(expr, expr->op, l);
 			break;
 		}
 		break;
diff --git a/expr.c b/expr.c
index 1e49e4f..903aef8 100644
--- a/expr.c
+++ b/expr.c
@@ -972,7 +972,8 @@ unaryexpr(struct scope *s)
 			error(&tok.loc, "operand of unary '-' operator must have arithmetic type");
 		if (e->type->prop & PROPINT)
 			e = exprpromote(e);
-		e = mkbinaryexpr(&tok.loc, TSUB, mkconstexpr(&typeint, 0), e);
+		e = mkexpr(EXPRUNARY, e->type, e);
+		e->op = op;
 		break;
 	case TBNOT:
 		next();
diff --git a/qbe.c b/qbe.c
index e8d9c13..81ed566 100644
--- a/qbe.c
+++ b/qbe.c
@@ -801,6 +801,9 @@ funcexpr(struct func *f, struct expr *e)
 		case TMUL:
 			r = funcexpr(f, e->base);
 			return funcload(f, e->type, (struct lvalue){r});
+		case TSUB:
+			r = funcexpr(f, e->base);
+			return funcinst(f, ISUB, qbetype(e->type).base, mkintconst(0), r);
 		}
 		fatal("internal error; unknown unary expression");
 		break;
diff --git a/test/const-expr-neg.c b/test/const-expr-neg.c
new file mode 100644
index 0000000..0918aa9
--- /dev/null
+++ b/test/const-expr-neg.c
@@ -0,0 +1 @@
+double x = -0.0;
diff --git a/test/const-expr-neg.qbe b/test/const-expr-neg.qbe
new file mode 100644
index 0000000..b380795
--- /dev/null
+++ b/test/const-expr-neg.qbe
@@ -0,0 +1 @@
+export data $x = align 8 { d d_-0, }