Add atomic_exchange

chibicc.h

@@ -221,6 +221,7 @@ typedef enum {
   ND_MEMZERO,   // Zero-clear a stack variable
   ND_ASM,       // "asm"
   ND_CAS,       // Atomic compare-and-swap
+  ND_EXCH,      // Atomic exchange
 } NodeKind;
 
 // AST node type

codegen.c

@@ -983,6 +983,16 @@ static void gen_expr(Node *node) {
     println("  movzbl %%cl, %%eax");
     return;
   }
+  case ND_EXCH: {
+    gen_expr(node->lhs);
+    push();
+    gen_expr(node->rhs);
+    pop("%rdi");
+
+    int sz = node->lhs->ty->base->size;
+    println("  xchg %s, (%%rdi)", reg_ax(sz));
+    return;
+  }
   }
 
   switch (node->lhs->ty->kind) {

include/stdatomic.h

@@ -7,4 +7,7 @@
 #define atomic_compare_exchange_strong(p, old, new) \
   __builtin_compare_and_swap((p), (old), (new))
 
+#define atomic_exchange(obj, val) __builtin_atomic_exchange(obj, val)
+#define atomic_exchange_explicit(obj, val, order) __builtin_atomic_exchange(obj, val)
+
 #endif

parse.c

@@ -2954,6 +2954,16 @@ static Node *primary(Token **rest, Token *tok) {
     return node;
   }
 
+  if (equal(tok, "__builtin_atomic_exchange")) {
+    Node *node = new_node(ND_EXCH, tok);
+    tok = skip(tok->next, "(");
+    node->lhs = assign(&tok, tok);
+    tok = skip(tok, ",");
+    node->rhs = assign(&tok, tok);
+    *rest = skip(tok, ")");
+    return node;
+  }
+
   if (tok->kind == TK_IDENT) {
     // Variable or enum constant
     VarScope *sc = find_var(tok);

test/atomic.c

@@ -38,6 +38,9 @@ static int add_millions(void) {
 int main() {
   ASSERT(3*1000*1000, add_millions());
 
+  ASSERT(3, ({ int x=3; atomic_exchange(&x, 5); }));
+  ASSERT(5, ({ int x=3; atomic_exchange(&x, 5); x; }));
+
   printf("OK\n");
   return 0;
 }

type.c

@@ -298,5 +298,10 @@ void add_type(Node *node) {
     if (node->cas_old->ty->kind != TY_PTR)
       error_tok(node->cas_old->tok, "pointer expected");
     return;
+  case ND_EXCH:
+    if (node->lhs->ty->kind != TY_PTR)
+      error_tok(node->cas_addr->tok, "pointer expected");
+    node->ty = node->lhs->ty->base;
+    return;
   }
 }