shithub: scc

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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.

--- a/cc1/cc1.h

+++ b/cc1/cc1.h

@@ -316,7 +316,7 @@

 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);

--- a/cc1/code.c

+++ b/cc1/code.c

@@ -313,7 +313,7 @@

 }

 Node *

-node(unsigned op, Type *tp, Node *left, Node *right)

+node(unsigned op, Type *tp, Node *lp, Node *rp)

 {

 	Node *np;

@@ -322,8 +322,14 @@

 	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;

 }

--- a/cc1/expr.c

+++ b/cc1/expr.c

@@ -845,6 +845,17 @@

 }

 Node *

+constexpr(void)

+{

+	Node *np;

+

+	np = ternary();

+	if (!np->constant)

+		error("constant expression required");

+	return np;

+}

+

+Node *

 expr(void)

 {

 	Node *lp, *rp;

-- 

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