Add missing file.

1 files changed, 124 insertions, 0 deletions

diff --git a/opt/fold.c b/opt/fold.c
new file mode 100644
index 0000000..bc5ffde
--- /dev/null
+++ b/opt/fold.c
@@ -0,0 +1,124 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <stdint.h>
+#include <stdarg.h>
+#include <ctype.h>
+#include <string.h>
+#include <assert.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+#include "parse.h"
+#include "opt.h"
+
+int islit(Node *n, vlong *v)
+{
+    Node *l;
+
+    if (exprop(n) != Olit)
+	return 0;
+    l = n->expr.args[0];
+    if (l->lit.littype != Lint)
+	return 0;
+    *v = l->lit.intval;
+    return 1;
+}
+
+int isval(Node *n, vlong val)
+{
+    vlong v;
+
+    if (!islit(n, &v))
+	return 0;
+    return v == val;
+}
+
+Node *val(int line, vlong val)
+{
+    Node *n;
+
+    n = mkint(line, val);
+    n = mkexpr(line, Olit, n, NULL);
+    return n;
+}
+
+Node *fold(Node *n)
+{
+    Node **args, *r;
+    vlong a, b;
+    size_t i;
+    
+    assert(n->type == Nexpr);
+
+    r = NULL;
+    args = n->expr.args;
+    if (exprop(n) != Ovar && exprop(n) != Ocjmp &&
+	exprop(n) != Ojmp && exprop(n) != Olit)
+	for (i = 0; i < n->expr.nargs; i++)
+	    args[i] = fold(args[i]);
+    switch (exprop(n)) {
+	case Ovar:
+	    /* FIXME: chase small consts */
+	    break;
+	case Oadd:
+	    /* x + 0 = 0 */
+	    if (isval(args[0], 0))
+		r = args[1];
+	    if (isval(args[1], 0))
+		r = args[0];
+	    if (islit(args[0], &a) && islit(args[1], &b))
+		r = val(n->line, a + b);
+	    break;
+	case Osub:
+	    /* x - 0 = 0 */
+	    if (isval(args[1], 0))
+		r = args[0];
+	    if (islit(args[0], &a) && islit(args[1], &b))
+		r = val(n->line, a - b);
+	    break;
+	case Omul:
+	    /* 1 * x = x */
+	    if (isval(args[0], 1))
+		r = args[1];
+	    if (isval(args[1], 1))
+		r = args[0];
+	    /* 0 * x = 0 */
+	    if (isval(args[0], 0))
+		r = args[0];
+	    if (isval(args[1], 0))
+		r = args[1];
+	    if (islit(args[0], &a) && islit(args[1], &b))
+		r = val(n->line, a * b);
+	    break;
+	case Odiv:
+	    /* x/1 = x */
+	    if (isval(args[1], 1))
+		r = args[0];
+	    /* 0/x = 0 */
+	    if (isval(args[1], 0))
+		r = args[1];
+	    if (islit(args[0], &a) && islit(args[1], &b))
+		r = val(n->line, a / b);
+	    break;
+	case Omod:
+	    /* x%1 = x */
+	    if (isval(args[1], 0))
+		r = args[0];
+	    if (islit(args[0], &a) && islit(args[1], &b))
+		r = val(n->line, a % b);
+	    break;
+	case Oneg:
+	    if (islit(args[0], &a))
+		r = val(n->line, -a);
+	    break;
+	default:
+	    break;
+    }
+
+    if (r)
+	return r;
+    else
+	return n;
+}