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kconfig: add comments to expression transformations

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Provide explanations for complex transformations.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
This commit is contained in:
Masahiro Yamada 2024-09-08 21:43:18 +09:00
parent d607e0e7a8
commit 4fa146eaec
1 changed files with 37 additions and 6 deletions
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43
scripts/kconfig/expr.c
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@ -442,6 +442,7 @@ static struct expr *expr_join_or(struct expr *e1, struct expr *e2)
}
}
if (sym1->type == S_BOOLEAN) {
// a || !a -> y
if ((e1->type == E_NOT && e1->left.expr->type == E_SYMBOL && e2->type == E_SYMBOL) ||
(e2->type == E_NOT && e2->left.expr->type == E_SYMBOL && e1->type == E_SYMBOL))
return expr_alloc_symbol(&symbol_yes);
@ -647,6 +648,30 @@ struct expr *expr_eliminate_dups(struct expr *e)
* Performs various simplifications involving logical operators and
* comparisons.
*
* For bool type:
* A=n -> !A
* A=m -> n
* A=y -> A
* A!=n -> A
* A!=m -> y
* A!=y -> !A
*
* For any type:
* !!A -> A
* !(A=B) -> A!=B
* !(A!=B) -> A=B
* !(A<=B) -> A>B
* !(A>=B) -> A<B
* !(A<B) -> A>=B
* !(A>B) -> A<=B
* !(A || B) -> !A && !B
* !(A && B) -> !A || !B
*
* For constant:
* !y -> n
* !m -> m
* !n -> y
*
* Allocates and returns a new expression.
*/
struct expr *expr_transform(struct expr *e)
@ -674,12 +699,14 @@ struct expr *expr_transform(struct expr *e)
if (e->left.sym->type != S_BOOLEAN)
break;
if (e->right.sym == &symbol_no) {
// A=n -> !A
e->type = E_NOT;
e->left.expr = expr_alloc_symbol(e->left.sym);
e->right.sym = NULL;
break;
}
if (e->right.sym == &symbol_mod) {
// A=m -> n
printf("boolean symbol %s tested for 'm'? test forced to 'n'\n", e->left.sym->name);
e->type = E_SYMBOL;
e->left.sym = &symbol_no;
@ -687,6 +714,7 @@ struct expr *expr_transform(struct expr *e)
break;
}
if (e->right.sym == &symbol_yes) {
// A=y -> A
e->type = E_SYMBOL;
e->right.sym = NULL;
break;
@ -696,11 +724,13 @@ struct expr *expr_transform(struct expr *e)
if (e->left.sym->type != S_BOOLEAN)
break;
if (e->right.sym == &symbol_no) {
// A!=n -> A
e->type = E_SYMBOL;
e->right.sym = NULL;
break;
}
if (e->right.sym == &symbol_mod) {
// A!=m -> y
printf("boolean symbol %s tested for 'm'? test forced to 'y'\n", e->left.sym->name);
e->type = E_SYMBOL;
e->left.sym = &symbol_yes;
@ -708,6 +738,7 @@ struct expr *expr_transform(struct expr *e)
break;
}
if (e->right.sym == &symbol_yes) {
// A!=y -> !A
e->type = E_NOT;
e->left.expr = expr_alloc_symbol(e->left.sym);
e->right.sym = NULL;
@ -717,7 +748,7 @@ struct expr *expr_transform(struct expr *e)
case E_NOT:
switch (e->left.expr->type) {
case E_NOT:
// !!a -> a
// !!A -> A
tmp = e->left.expr->left.expr;
free(e->left.expr);
free(e);
@ -726,7 +757,7 @@ struct expr *expr_transform(struct expr *e)
break;
case E_EQUAL:
case E_UNEQUAL:
// !a='x' -> a!='x'
// !(A=B) -> A!=B
tmp = e->left.expr;
free(e);
e = tmp;
@ -734,7 +765,7 @@ struct expr *expr_transform(struct expr *e)
break;
case E_LEQ:
case E_GEQ:
// !a<='x' -> a>'x'
// !(A<=B) -> A>B
tmp = e->left.expr;
free(e);
e = tmp;
@ -742,14 +773,14 @@ struct expr *expr_transform(struct expr *e)
break;
case E_LTH:
case E_GTH:
// !a<'x' -> a>='x'
// !(A<B) -> A>=B
tmp = e->left.expr;
free(e);
e = tmp;
e->type = e->type == E_LTH ? E_GEQ : E_LEQ;
break;
case E_OR:
// !(a || b) -> !a && !b
// !(A || B) -> !A && !B
tmp = e->left.expr;
e->type = E_AND;
e->right.expr = expr_alloc_one(E_NOT, tmp->right.expr);
@ -758,7 +789,7 @@ struct expr *expr_transform(struct expr *e)
e = expr_transform(e);
break;
case E_AND:
// !(a && b) -> !a || !b
// !(A && B) -> !A || !B
tmp = e->left.expr;
e->type = E_OR;
e->right.expr = expr_alloc_one(E_NOT, tmp->right.expr);