implemented thiscall by copying logic from fastcall

implemented improved thiscall by using mov ecx instead of pop ecx

include __thiscall and __thiscall__ as aliases

remove fake line in test

i386-gen.c

@@ -410,6 +410,8 @@ ST_FUNC void gfunc_call(int nb_args)
 {
     int size, align, r, args_size, i, func_call;
     Sym *func_sym;
+    // Look ahead to the function on the stack to get the function call type
+    int func_call2 = ((vtop - nb_args)->type.ref)->f.func_call;
 
 #ifdef CONFIG_TCC_BCHECK
     if (tcc_state->do_bounds_check)
@@ -418,6 +420,12 @@ ST_FUNC void gfunc_call(int nb_args)
 
     args_size = 0;
     for(i = 0;i < nb_args; i++) {
+        if (func_call2 == FUNC_THISCALL && i == (nb_args - 1)) {
+            // If thiscall, zap the last push, as it is `this`. Instead, mov into ecx
+            size = 0;
+            load(get_reg(RC_ECX), vtop);
+        }
+        else 
         if ((vtop->type.t & VT_BTYPE) == VT_STRUCT) {
             size = type_size(&vtop->type, &align);
             /* align to stack align size */
@@ -503,7 +511,7 @@ ST_FUNC void gfunc_call(int nb_args)
 
     gcall_or_jmp(0);
 
-    if (args_size && func_call != FUNC_STDCALL && func_call != FUNC_FASTCALLW)
+    if (args_size && func_call != FUNC_STDCALL && func_call != FUNC_THISCALL && func_call != FUNC_FASTCALLW)
         gadd_sp(args_size);
     vtop--;
 }
@@ -523,6 +531,7 @@ ST_FUNC void gfunc_prolog(Sym *func_sym)
     const uint8_t *fastcall_regs_ptr;
     Sym *sym;
     CType *type;
+    int thiscall_nb_regs;
 
     sym = func_type->ref;
     func_call = sym->f.func_call;
@@ -540,6 +549,11 @@ ST_FUNC void gfunc_prolog(Sym *func_sym)
         fastcall_nb_regs = 0;
         fastcall_regs_ptr = NULL;
     }
+
+    if (func_call == FUNC_THISCALL) {
+        thiscall_nb_regs = 1;
+    }
+
     param_index = 0;
 
     ind += FUNC_PROLOG_SIZE;
@@ -575,6 +589,14 @@ ST_FUNC void gfunc_prolog(Sym *func_sym)
             o(0x89);     /* movl */
             gen_modrm(fastcall_regs_ptr[param_index], VT_LOCAL, NULL, loc);
             param_addr = loc;
+        } 
+        else if(param_index < thiscall_nb_regs) {
+            /* Why ? */
+            /* save THISCALL register; ECX */
+            loc -= 4;
+            o(0x89);     /* movl */
+            gen_modrm(TREG_ECX, VT_LOCAL, NULL, loc);
+            param_addr = loc;
         } else {
             param_addr = addr;
             addr += size;
@@ -585,7 +607,7 @@ ST_FUNC void gfunc_prolog(Sym *func_sym)
     }
     func_ret_sub = 0;
     /* pascal type call or fastcall ? */
-    if (func_call == FUNC_STDCALL || func_call == FUNC_FASTCALLW)
+    if (func_call == FUNC_STDCALL || func_call == FUNC_FASTCALLW || func_call == FUNC_THISCALL)
         func_ret_sub = addr - 8;
 #if !defined(TCC_TARGET_PE) && !TARGETOS_FreeBSD || TARGETOS_OpenBSD
     else if (func_vc)

tcc.h

@@ -634,6 +634,7 @@ typedef struct DLLReference {
 #define FUNC_FASTCALL2 3 /* first parameters in %eax, %edx */
 #define FUNC_FASTCALL3 4 /* first parameter in %eax, %edx, %ecx */
 #define FUNC_FASTCALLW 5 /* first parameter in %ecx, %edx */
+#define FUNC_THISCALL  6 /* first param in %ecx */
 
 /* field 'Sym.t' for macros */
 #define MACRO_OBJ      0 /* object like macro */

tccgen.c

@@ -3974,7 +3974,12 @@ static void parse_attribute(AttributeDef *ad)
         case TOK_FASTCALL2:
         case TOK_FASTCALL3:
             ad->f.func_call = FUNC_FASTCALLW;
-            break;            
+            break;    
+        case TOK_THISCALL1:
+        case TOK_THISCALL2:
+        case TOK_THISCALL3:
+            ad->f.func_call = FUNC_THISCALL;
+            break;        
 #endif
         case TOK_MODE:
             skip('(');

tcctok.h

@@ -135,6 +135,9 @@
      DEF(TOK_FASTCALL1, "fastcall")
      DEF(TOK_FASTCALL2, "__fastcall")
      DEF(TOK_FASTCALL3, "__fastcall__")
+     DEF(TOK_THISCALL1, "thiscall")
+     DEF(TOK_THISCALL2, "__thiscall")
+     DEF(TOK_THISCALL3, "__thiscall__")
      DEF(TOK_REGPARM1, "regparm")
      DEF(TOK_REGPARM2, "__regparm__")
      DEF(TOK_CLEANUP1, "cleanup")

tests/thiscall/thiscall-test.c

@@ -0,0 +1,17 @@
+#ifndef __thiscall
+  #define __thiscall __attribute__((thiscall))
+#endif
+#ifndef __cdecl
+  #define __cdecl __attribute__((cdecl))  
+#endif
+#ifndef __stdcall
+  #define __stdcall __attribute__((stdcall))  
+#endif
+
+void ( __thiscall * const thisCall1 ) ( void * _this, int a ) = ( void ( __thiscall * ) ( void * _this, int a ) ) 0x4788a0;
+
+int main() {
+  thisCall1((void*) 0xDEADBEEF, 1000);
+
+  return 1;
+}