fix: not code generation is wrong

Author: mopp

src/codegen.c

@@ -66,10 +66,11 @@ static void gen(Node const* node)
 
     if (node->ty == '!') {
         gen(node->lhs);
+        printf("  xor rdx, rdx\n");
         printf("  pop rax\n");
         printf("  cmp rax, 0\n");
-        printf("  sete al\n");
-        printf("  push rax\n");
+        printf("  sete dl\n");
+        printf("  push rdx\n");
 
         return;
     }

test.sh

@@ -216,3 +216,4 @@ try 0   "void* foo(size_t n) { return n - 1229801703532086340; } int main(void)
 try 0   "int main(void) { void** data = 0; return data + 0;}"
 try 8   "int main(void) { void** data = 0; size_t i = 1; return data + i++;}"
 try 1   "int main(void) { int i = 1 != 0 &&  1 < 10; return i; }"
+try 10  "int main(void) { char* q = 10576963; if (!q) {return 0;} return 10; }"