Add <pointer> + <number> and <pointer> - <number>.

9cc.h

@@ -132,6 +132,7 @@ typedef struct Node {
 } Node;
 
 Vector *parse(Vector *tokens);
+int size_of(Type *ty);
 
 /// sema.c
 

gen_ir.c

@@ -173,9 +173,23 @@ static int gen_expr(Node *node) {
     return lhs;
   }
   case '+':
-    return gen_binop(IR_ADD, node->lhs, node->rhs);
-  case '-':
-    return gen_binop(IR_SUB, node->lhs, node->rhs);
+  case '-': {
+    int insn = (node->op == '+') ? IR_ADD : IR_SUB;
+
+    if (node->lhs->ty->ty != PTR)
+      return gen_binop(insn, node->lhs, node->rhs);
+
+    int rhs = gen_expr(node->rhs);
+    int r = nreg++;
+    add(IR_IMM, r, size_of(node->lhs->ty->ptr_of));
+    add(IR_MUL, rhs, r);
+    kill(r);
+
+    int lhs = gen_expr(node->lhs);
+    add(insn, lhs, rhs);
+    kill(rhs);
+    return lhs;
+  }
   case '*':
     return gen_binop(IR_MUL, node->lhs, node->rhs);
   case '/':

sema.c

@@ -10,6 +10,19 @@ typedef struct {
 static Map *vars;
 static int stacksize;
 
+int size_of(Type *ty) {
+  if (ty->ty == INT)
+    return 4;
+  assert(ty->ty == PTR);
+  return 8;
+}
+
+static void swap(Node **p, Node **q) {
+  Node *r = *p;
+  *p = *q;
+  *q = r;
+}
+
 static void walk(Node *node) {
   switch (node->op) {
   case ND_NUM:
@@ -49,11 +62,17 @@ static void walk(Node *node) {
     walk(node->body);
     return;
   case '+':
+  case '-':
     walk(node->lhs);
     walk(node->rhs);
+
+    if (node->rhs->ty->ty == PTR)
+      swap(&node->lhs, &node->rhs);
+    if (node->rhs->ty->ty == PTR)
+      error("'pointer %c pointer' is not defined", node->op);
+
     node->ty = node->lhs->ty;
     return;
-  case '-':
   case '*':
   case '/':
   case '=':
@@ -65,6 +84,11 @@ static void walk(Node *node) {
     node->ty = node->lhs->ty;
     return;
   case ND_DEREF:
+    walk(node->expr);
+    if (node->expr->ty->ty != PTR)
+      error("operand must be a pointer");
+    node->ty = node->expr->ty->ptr_of;
+    return;
   case ND_RETURN:
     walk(node->expr);
     return;

test.sh

@@ -19,11 +19,29 @@ try() {
 cat <<EOF | gcc -xc -c -o tmp-test.o -
 int plus(int x, int y) { return x + y; }
 
-int *alloc(int x) {
-  static int arr[1];
+int *alloc1(int x, int y) {
+  static int arr[2];
   arr[0] = x;
+  arr[1] = y;
   return arr;
 }
+
+int *alloc2(int x, int y) {
+  static int arr[2];
+  arr[0] = x;
+  arr[1] = y;
+  return arr + 1;
+}
+
+int **alloc_ptr_ptr(int x) {
+  static int **p;
+  static int *q;
+  static int r;
+  r = x;
+  q = &r;
+  p = &q;
+  return p;
+}
 EOF
 
 try 1 'int main() { return 1; }'
@@ -73,6 +91,8 @@ try 1 'int main() { return 1>0; }'
 try 60 'int main() { int sum=0; int i; for (i=10; i<15; i=i+1) sum = sum + i; return sum;}'
 try 89 'int main() { int i=1; int j=1; for (int k=0; k<10; k=k+1) { int m=i+j; i=j; j=m; } return i;}'
 
-try 42 'int main() { int *p = alloc(42); return *p; }'
+try 8 'int main() { int *p = alloc1(3, 5); return *p + *(p + 1); }'
+try 9 'int main() { int *p = alloc2(2, 7); return *p + *(p - 1); }'
+try 2 'int main() { int **p = alloc_ptr_ptr(2); return **p; }'
 
 echo OK