kconfig: call expr_eliminate_yn() at least once in expr_eliminate_dups()

Kconfig simplifies expressions, but redundant '&&' and '||' operators
involving constant symbols 'y' and 'n' are sometimes trimmed and
sometimes not.

[Test Code]

    config DEP
            def_bool y

    config A
            bool "A"
            depends on DEP && y

    config B
            bool "B"
            depends on DEP && y && y

[Result]

    $ make helpnewconfig
      [ snip ]
    -----

    There is no help available for this option.
    Symbol: A [=n]
    Type  : bool
    Defined at Kconfig:4
      Prompt: A
      Depends on: DEP [=y] && y [=y]
      Location:
        -> A (A [=n])

    -----
    -----

    There is no help available for this option.
    Symbol: B [=n]
    Type  : bool
    Defined at Kconfig:8
      Prompt: B
      Depends on: DEP [=y]
      Location:
        -> B (B [=n])

    -----

The dependency for A, 'DEP && y', remains as-is, while that for B,
'DEP && y && y', has been reduced to 'DEP'.

Currently, expr_eliminate_dups() calls expr_eliminate_yn() only when
trans_count != 0, in other words, only when expr_eliminate_dups1() has
trimmed at least one leaf. It fails to trim a single '&& y', etc.

To fix this inconsistent behavior, expr_eliminate_yn() should be called
at least once even if no leaf has been trimmed.

Signed-off-by: Masahiro Yamada <[email protected]>

Author: masahir0y

scripts/kconfig/expr.c

@@ -637,19 +637,16 @@ struct expr *expr_eliminate_dups(struct expr *e)
 		return e;
 
 	oldcount = trans_count;
-	while (1) {
+	do {
 		trans_count = 0;
 		switch (e->type) {
 		case E_OR: case E_AND:
 			expr_eliminate_dups1(e->type, &e, &e);
 		default:
 			;
 		}
-		if (!trans_count)
-			/* No simplifications done in this pass. We're done */
-			break;
 		e = expr_eliminate_yn(e);
-	}
+	} while (trans_count); /* repeat until we get no more simplifications */
 	trans_count = oldcount;
 	return e;
 }