[hackers] [scc] Naive implementation of constexpr() || Roberto E. Vargas Caballero

From: <git_AT_suckless.org>
Date: Sat, 18 Jul 2015 10:27:46 +0200 (CEST)

commit d897f1e478283d1fc1a71ac9637056c190a2da3f
Author: Roberto E. Vargas Caballero <k0ga_AT_shike2.com>
AuthorDate: Sat Jul 18 10:06:21 2015 +0200
Commit: Roberto E. Vargas Caballero <k0ga_AT_shike2.com>
CommitDate: Sat Jul 18 10:06:21 2015 +0200

    Naive implementation of constexpr()
    
    Constexpr() parses a constant expression, an expression
    which can be evaluated at compile time. This is a naive
    and incorrect implementation, because it marks as constant
    expressions where no variables are used, but it is wrong.
    For example:
    
            - static int a; -> &a is a constant expression.
            - static int v[10]; -> &v[3] is a constant expression
            - int f(void); -> f is a constant expression.
    But
            - &v[a] is not a constant expression.
            - &v[f()] is not a constant expression.

diff --git a/cc1/cc1.h b/cc1/cc1.h
index 1f1d7f4..a2f60cb 100644
--- a/cc1/cc1.h
+++ b/cc1/cc1.h
_AT_@ -316,7 +316,7 @@ extern Node *sizeofnode(Type *tp);
 extern void freetree(Node *np);
 
 /* expr.c */
-extern Node *expr(void), *negate(Node *np);
+extern Node *expr(void), *negate(Node *np), *constexpr(void);
 
 /* cpp.c */
 extern void icpp(void);
diff --git a/cc1/code.c b/cc1/code.c
index 7c70401..1d28b62 100644
--- a/cc1/code.c
+++ b/cc1/code.c
_AT_@ -313,7 +313,7 @@ emitfield(unsigned op, void *arg)
 }
 
 Node *
-node(unsigned op, Type *tp, Node *left, Node *right)
+node(unsigned op, Type *tp, Node *lp, Node *rp)
 {
         Node *np;
 
_AT_@ -322,8 +322,14 @@ node(unsigned op, Type *tp, Node *left, Node *right)
         np->type = tp;
         np->sym = NULL;
         np->constant = np->symbol = np->lvalue = 0;
- np->left = left;
- np->right = right;
+ np->left = lp;
+ np->right = rp;
+
+ if (lp)
+ np->constant |= lp->constant;
+ if (rp)
+ np->constant |= rp->constant;
+
         return np;
 }
 
diff --git a/cc1/expr.c b/cc1/expr.c
index d32f098..fe2de95 100644
--- a/cc1/expr.c
+++ b/cc1/expr.c
_AT_@ -845,6 +845,17 @@ assign(void)
 }
 
 Node *
+constexpr(void)
+{
+ Node *np;
+
+ np = ternary();
+ if (!np->constant)
+ error("constant expression required");
+ return np;
+}
+
+Node *
 expr(void)
 {
         Node *lp, *rp;
Received on Sat Jul 18 2015 - 10:27:46 CEST