On 10/30/23 21:35, Fei Gao wrote:
So just a few notes to further illustrate why I'm currently looking to
take the VRULL+Ventana implementation. The code above would be much
better handled by just calling noce_emit_cmove. noce_emit_cmove will go
through the conditional move expander. So any improvement we make in
the expander "just work" when called from the if-converter.
noce_emit_czero is used here to make sure czero insns are emited.
noce_emit_cmove includes SFB and Thead movcc, which will take precedence
over zicond in RISCV if enabled. Unfortunately we have products with SFB and
Zicond
both available and saw such conflict.
And that is also the reason to add hook TARGET_HAVE_COND_ZERO
in [PATCH 1/4] to disallow ineffient code emited by SFB enable and Zicond
disabled case.
I understand what you're trying to do, but I would consider the
TARGET_HAVE_COND_ZERO fundamentally the wrong approach.
I'm willing to defer routing everything through noce_emit_cmove for now,
but that's really where this code needs to be going. If that's causing
a conflict for a particular implementation with both SFB and Zicond,
then we'll have to look at the details and adjust things in the target
files.
Cool and waiting for your submit. Shifts/rotates can be added in
noce_try_cond_zero_arith.
Fully agreed. Those are easy.
I tried to keep noce_try_cond_zero_arith simple without introducing SCC and
other stuff
as addtional insns will be generated for greater than like comparision
but may not be generated for branch-insn based SFB.
And I think the result is we're going to fail to implement many
profitable if-conversions.
Jeff
