On 7/3/24 8:07 PM, Li, Pan2 wrote:
But if you look at what the hardware can actually support, it doesn't
have HImode or QImode operations other than load/store and for rv64
there are no SImode logicals.
That's what WORD_REGISTER_OPERATIONS is designed to support. Regardless
of what happens at the source level, the generic parts of gimple->RTL
expansion arrange to widen the types appropriately.
I haven't looked at the expansion of the SAT_* builtins, but the way
this is generally supposed to work is you just have to have your
expander only accept the modes the processor actually supports and
generic code will handle the widening for you.
Thanks Jeff.
Got it, you mean the widening ops will be covered automatically before
expanding.
That's what happens for most basic operations. The caveat here is
you're not going to be going through the standard expander paths. It's
one of the unfortunate downsides of builtins/intrinsics, so we may need
to do something a bit special as a result.
I am not sure which part take care auto-widening, but the SAT_TRUNC expands
from middle end may look
like below.
Could you please help to enlighten me is there something missing here ?
static void
match_unsigned_saturation_trunc (gimple_stmt_iterator *gsi, gassign *stmt)
{
tree ops[1];
tree lhs = gimple_assign_lhs (stmt);
tree type = TREE_TYPE (lhs);
if (gimple_unsigned_integer_sat_trunc (lhs, ops, NULL)
&& direct_internal_fn_supported_p (IFN_SAT_TRUNC,
tree_pair (type, TREE_TYPE (ops[0])),
OPTIMIZE_FOR_BOTH))
{
gcall *call = gimple_build_call_internal (IFN_SAT_TRUNC, 1, ops[0]);
gimple_call_set_lhs (call, lhs);
gsi_replace (gsi, call, /* update_eh_info */ true);
}
}
Right. That's what I was worried about. It essentially just asks the
backend "do you have this operation with this set of modes" without any
of the widening bits like you'd find in expand_binop.
We ran into this with the CRC work as well.
What this means is is that you'll have to do the widening operations in
the RISC-V expander. Essentially for an argument smaller than word_mode
you'd want to widen to word_mode while retaining the right semantics.
jeff
