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[qfcc] Propagate double-negative through addition

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And convert addition to subtraction when extend expressions are not
involved. This has taken my little test down to 56 instructions total
(21 for `l p ~l`), down from 74 (39).
This commit is contained in:
Bill Currie 2023-09-02 19:42:33 +09:00
parent c2472e99fa
commit b514bbdb44
1 changed files with 35 additions and 2 deletions
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37
tools/qfcc/source/expr_algebra.c
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@ -74,6 +74,14 @@ ext_expr (expr_t *src, type_t *type, int extend, bool reverse)
return new_extend_expr (src, type, extend, reverse); return new_extend_expr (src, type, extend, reverse);
} }
static bool __attribute__((const))
anti_com (const expr_t *e)
{
return (e->type == ex_expr
&& (e->e.expr.op == CROSS || e->e.expr.op == WEDGE
|| e->e.expr.op == '-'));
}
static expr_t * static expr_t *
neg_expr (expr_t *e) neg_expr (expr_t *e)
{ {
@ -85,7 +93,11 @@ neg_expr (expr_t *e)
return e->e.expr.e1; return e->e.expr.e1;
} }
auto type = get_type (e); auto type = get_type (e);
e = new_unary_expr ('-', e); if (anti_com (e)) {
e = new_binary_expr (e->e.expr.op, e->e.expr.e2, e->e.expr.e1);
} else {
e = new_unary_expr ('-', e);
}
e->e.expr.type = type; e->e.expr.type = type;
return fold_constants (e); return fold_constants (e);
} }
@ -361,8 +373,29 @@ sum_expr (type_t *type, expr_t *a, expr_t *b)
} }
} }
} }
auto sum = new_binary_expr ('+', a, b); bool neg = false;
if ((is_neg (a) && (is_neg (b) || anti_com (b)))
|| (anti_com (a) && is_neg (b))) {
neg = true;
a = neg_expr (a);
b = neg_expr (b);
}
int op = '+';
if (is_neg (a) && b->type != ex_extend) {
auto t = a;
a = b;
b = t;
op = '-';
b = neg_expr (b);
} else if (a->type != ex_extend && is_neg (b)) {
op = '-';
b = neg_expr (b);
}
auto sum = new_binary_expr (op, a, b);
sum->e.expr.type = type; sum->e.expr.type = type;
if (neg) {
sum = neg_expr (sum);
}
return sum; return sum;
} }