If the condition of a select is also a select, both with the same
arguments: first a non-zero constant, then a zero constant, then
the outer select is equivalent to the inner one and can thus
be replaced by the result of the inner select (which is its own
condition).
Note: this is a special case of:
SEL(SEL(x, C, 0), y, z) --> SEL(x, y, z)
and without this patch we'll have:
t = SEL(x, C, 0)
r = SEL(t, C, 0)
simplified into:
t = SEL(x, C, 0) // possibly unused now
r = SEL(x, C, 0)
but the present patch do
t = SEL(x, C, 0)
r = t
In other words, functionally, the result is the same but
now the result is taken from the first instruction.
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@xxxxxxxxx>
---
simplify.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/simplify.c b/simplify.c
index 6b44d447c0a9..1fcfc691579a 100644
--- a/simplify.c
+++ b/simplify.c
@@ -1791,8 +1791,11 @@ static int simplify_select(struct instruction *insn)
// And if that one results in a "zero or not", use the
// original conditional instead.
// SEL(SEL(x, C, 0), y, z) --> SEL(x, y, z)
+ // SEL(SEL(x, C, 0), C, 0) --> SEL(x, C, 0) == cond
// SEL(SEL(x, 0, C), y, z) --> SEL(x, z, y)
if (!def->src3->value) {
+ if ((src1 == def->src2) && (src2 == def->src3))
+ return replace_with_pseudo(insn, cond);
return replace_pseudo(insn, &insn->cond, def->cond);
}
if (!def->src2->value) {
--
2.29.2
