-fno-type-redefinition-check

don't catch redefinition for local vars. With this option on
    tcc accepts the following code:
    int main()
    {
        int a = 0;
        long a = 0;
    }
    But if you shure there is no problem with your local variables,
    then a compilation speed can be improved if you have a lots of
    the local variables (50000+)

libtcc.c

@@ -1764,6 +1764,7 @@ static const FlagDef flag_defs[] = {
     { offsetof(TCCState, old_struct_init_code), 0, "old-struct-init-code" },
     { offsetof(TCCState, dollars_in_identifiers), 0, "dollars-in-identifiers" },
     { offsetof(TCCState, normalize_inc_dirs), 0, "normalize-inc-dirs" },
+    { offsetof(TCCState, no_type_redef_check), FD_INVERT, "type-redefinition-check" },
 };
 
 /* set/reset a flag */

tcc.h

@@ -707,6 +707,7 @@ struct TCCState {
 				   Liuux 2.4.26 can't find initrd when compiled with a new algorithm */
     int dollars_in_identifiers;	/* allows '$' char in indentifiers */
     int normalize_inc_dirs;	/* remove non-existent or duplicate directories from include paths */
+    int no_type_redef_check;    /* no local vars redefinition check */
 
     /* warning switches */
     int warn_write_strings;

tccgen.c

@@ -166,11 +166,13 @@ ST_INLN void sym_free(Sym *sym)
 ST_FUNC Sym *sym_push2(Sym **ps, int v, int t, long c)
 {
     Sym *s;
-    if (ps == &local_stack) {
-        for (s = *ps; s && s != scope_stack_bottom; s = s->prev)
-            if (!(v & SYM_FIELD) && (v & ~SYM_STRUCT) < SYM_FIRST_ANOM && s->v == v)
-                tcc_error("incompatible types for redefinition of '%s'",
-                          get_tok_str(v, NULL));
+    if (!tcc_state->no_type_redef_check) {
+        if (ps == &local_stack) {
+            for (s = *ps; s && s != scope_stack_bottom; s = s->prev)
+                if (!(v & SYM_FIELD) && (v & ~SYM_STRUCT) < SYM_FIRST_ANOM && s->v == v)
+                    tcc_error("incompatible types for redefinition of '%s'",
+                              get_tok_str(v, NULL));
+        }
     }
     s = sym_malloc();
     s->asm_label = 0;