Allow to call a fucntion returning a struct

chibicc.h

@@ -222,6 +222,7 @@ struct Node {
   Type *func_ty;
   Node *args;
   bool pass_by_stack;
+  Obj *ret_buffer;
 
   // Goto or labeled statement
   char *label;

codegen.c

@@ -112,6 +112,12 @@ static void gen_addr(Node *node) {
     gen_addr(node->lhs);
     println("  add $%d, %%rax", node->member->offset);
     return;
+  case ND_FUNCALL:
+    if (node->ret_buffer) {
+      gen_expr(node);
+      return;
+    }
+    break;
   }
 
   error_tok(node->tok, "not an lvalue");
@@ -391,10 +397,16 @@ static void push_args2(Node *args, bool first_pass) {
 //
 // - If a function is variadic, set the number of floating-point type
 //   arguments to RAX.
-static int push_args(Node *args) {
+static int push_args(Node *node) {
   int stack = 0, gp = 0, fp = 0;
 
-  for (Node *arg = args; arg; arg = arg->next) {
+  // If the return type is a large struct/union, the caller passes
+  // a pointer to a buffer as if it were the first argument.
+  if (node->ret_buffer && node->ty->size > 16)
+    gp++;
+
+  // Load as many arguments to the registers as possible.
+  for (Node *arg = node->args; arg; arg = arg->next) {
     Type *ty = arg->ty;
 
     switch (ty->kind) {
@@ -437,11 +449,56 @@ static int push_args(Node *args) {
     stack++;
   }
 
-  push_args2(args, true);
-  push_args2(args, false);
+  push_args2(node->args, true);
+  push_args2(node->args, false);
+
+  // If the return type is a large struct/union, the caller passes
+  // a pointer to a buffer as if it were the first argument.
+  if (node->ret_buffer && node->ty->size > 16) {
+    println("  lea %d(%%rbp), %%rax", node->ret_buffer->offset);
+    push();
+  }
+
   return stack;
 }
 
+static void copy_ret_buffer(Obj *var) {
+  Type *ty = var->ty;
+  int gp = 0, fp = 0;
+
+  if (has_flonum1(ty)) {
+    assert(ty->size == 4 || 8 <= ty->size);
+    if (ty->size == 4)
+      println("  movss %%xmm0, %d(%%rbp)", var->offset);
+    else
+      println("  movsd %%xmm0, %d(%%rbp)", var->offset);
+    fp++;
+  } else {
+    for (int i = 0; i < MIN(8, ty->size); i++) {
+      println("  mov %%al, %d(%%rbp)", var->offset + i);
+      println("  shr $8, %%rax");
+    }
+    gp++;
+  }
+
+  if (ty->size > 8) {
+    if (has_flonum2(ty)) {
+      assert(ty->size == 12 || ty->size == 16);
+      if (ty->size == 12)
+        println("  movss %%xmm%d, %d(%%rbp)", fp, var->offset + 8);
+      else
+        println("  movsd %%xmm%d, %d(%%rbp)", fp, var->offset + 8);
+    } else {
+      char *reg1 = (gp == 0) ? "%al" : "%dl";
+      char *reg2 = (gp == 0) ? "%rax" : "%rdx";
+      for (int i = 8; i < MIN(16, ty->size); i++) {
+        println("  mov %s, %d(%%rbp)", reg1, var->offset + i);
+        println("  shr $8, %s", reg2);
+      }
+    }
+  }
+}
+
 // Generate code for a given node.
 static void gen_expr(Node *node) {
   println("  .loc %d %d", node->tok->file->file_no, node->tok->line_no);
@@ -578,10 +635,16 @@ static void gen_expr(Node *node) {
     return;
   }
   case ND_FUNCALL: {
-    int stack_args = push_args(node->args);
+    int stack_args = push_args(node);
     gen_expr(node->lhs);
 
     int gp = 0, fp = 0;
+
+    // If the return type is a large struct/union, the caller passes
+    // a pointer to a buffer as if it were the first argument.
+    if (node->ret_buffer && node->ty->size > 16)
+      pop(argreg64[gp++]);
+
     for (Node *arg = node->args; arg; arg = arg->next) {
       Type *ty = arg->ty;
 
@@ -646,6 +709,14 @@ static void gen_expr(Node *node) {
         println("  movswl %%ax, %%eax");
       return;
     }
+
+    // If the return type is a small struct, a value is returned
+    // using up to two registers.
+    if (node->ret_buffer && node->ty->size <= 16) {
+      copy_ret_buffer(node->ret_buffer);
+      println("  lea %d(%%rbp), %%rax", node->ret_buffer->offset);
+    }
+
     return;
   }
   }

parse.c

@@ -2236,6 +2236,11 @@ static Node *funcall(Token **rest, Token *tok, Node *fn) {
   node->func_ty = ty;
   node->ty = ty->return_ty;
   node->args = head.next;
+
+  // If a function returns a struct, it is caller's responsibility
+  // to allocate a space for the return value.
+  if (node->ty->kind == TY_STRUCT || node->ty->kind == TY_UNION)
+    node->ret_buffer = new_lvar("", node->ty);
   return node;
 }
 

test/common

@@ -92,3 +92,26 @@ int struct_test7(Ty7 x, int n) {
   default: return x.c;
   }
 }
+
+Ty4 struct_test24(void) {
+  return (Ty4){10, 20, 30, 40};
+}
+
+Ty5 struct_test25(void) {
+  return (Ty5){10, 20, 30};
+}
+
+Ty6 struct_test26(void) {
+  return (Ty6){10, 20, 30};
+}
+
+typedef struct { unsigned char a[10]; } Ty20;
+typedef struct { unsigned char a[20]; } Ty21;
+
+Ty20 struct_test27(void) {
+  return (Ty20){10, 20, 30, 40, 50, 60, 70, 80, 90, 100};
+}
+
+Ty21 struct_test28(void) {
+  return (Ty21){1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20};
+}

test/function.c

@@ -168,6 +168,15 @@ int struct_test15(Ty5 x, int n) {
   }
 }
 
+typedef struct { unsigned char a[10]; } Ty20;
+typedef struct { unsigned char a[20]; } Ty21;
+
+Ty4 struct_test24(void);
+Ty5 struct_test25(void);
+Ty6 struct_test26(void);
+Ty20 struct_test27(void);
+Ty21 struct_test28(void);
+
 int main() {
   ASSERT(3, ret3());
   ASSERT(8, add2(3, 5));
@@ -288,6 +297,29 @@ int main() {
   ASSERT(20, ({ Ty5 x={10,20,30}; struct_test15(x, 1); }));
   ASSERT(30, ({ Ty5 x={10,20,30}; struct_test15(x, 2); }));
 
+  ASSERT(10, struct_test24().a);
+  ASSERT(20, struct_test24().b);
+  ASSERT(30, struct_test24().c);
+  ASSERT(40, struct_test24().d);
+
+  ASSERT(10, struct_test25().a);
+  ASSERT(20, struct_test25().b);
+  ASSERT(30, struct_test25().c);
+
+  ASSERT(10, struct_test26().a[0]);
+  ASSERT(20, struct_test26().a[1]);
+  ASSERT(30, struct_test26().a[2]);
+
+  ASSERT(10, struct_test27().a[0]);
+  ASSERT(60, struct_test27().a[5]);
+  ASSERT(100, struct_test27().a[9]);
+
+  ASSERT(1, struct_test28().a[0]);
+  ASSERT(5, struct_test28().a[4]);
+  ASSERT(10, struct_test28().a[9]);
+  ASSERT(15, struct_test28().a[14]);
+  ASSERT(20, struct_test28().a[19]);
+
   printf("OK\n");
   return 0;
 }