What about that? I guess I don't really know how to determine if a
block is EMPTY?
diff --git a/gcc/config/riscv/riscv-vsetvl.cc b/gcc/config/riscv/riscv-vsetvl.cc
index 682f795c8e1..784ab184c72 100644
--- a/gcc/config/riscv/riscv-vsetvl.cc
+++ b/gcc/config/riscv/riscv-vsetvl.cc
@@ -3282,6 +3282,10 @@ pass_vsetvl::earliest_fusion (void)
if (src_block_info.reaching_out.unknown_p ())
break;
+ if (vsetvl_insn_p (expr.get_insn ()->rtl ())
+ && src_block_info.reaching_out.empty_p ())
+ continue;
+
gcc_assert (!(eg->flags & EDGE_ABNORMAL));
vector_insn_info new_info = vector_insn_info ();
profile_probability prob = src_block_info.probability;
On Mon, Aug 28, 2023 at 5:09 PM [email protected]
<[email protected]> wrote:
>
> No. we can't.
>
> My goal is to forbid this following situation:
>
> bb 2:
> EMPTY (no any vsetvl and rvv insn)
> bb 3:
> user vsetvl.
>
> We forbid user vsetvl (bb 3) be move to bb 2 in earliest fusion since user
> vsetvl has no side effects
> and we believe user vsetvl in bb 3 here is early enough.
>
> However, if we skip that as your patch, we will end up with missing this
> optimization:
>
> bb 2:
> user vsetvl a5, a4, e8, mf4...
> vle8
> vse8
>
> bb 3:
> user vsetvl a5, a4, e16, mf2... -----> In phase 1 && phase 2, the local
> demand fusion will update it into (e32, m1)
> vle32
> vadd
> vse32
>
> If we skip at the top, we will be missing fuse user vsetvl (in bb 3 e32 m1)
> into user vsetvl (in bb 2 e8 mf4).
>
> Thanks.
>
>
> [email protected]
>
> From: Kito Cheng
> Date: 2023-08-28 16:58
> To: Robin Dapp
> CC: Juzhe-Zhong; gcc-patches; kito.cheng
> Subject: Re: [PATCH] RISC-V: Disable user vsetvl fusion into EMPTY block
> Is it possible to skip that at the topper level like that?
>
> diff --git a/gcc/config/riscv/riscv-vsetvl.cc
> b/gcc/config/riscv/riscv-vsetvl.cc
> index 682f795c8e1..654d25de593 100644
> --- a/gcc/config/riscv/riscv-vsetvl.cc
> +++ b/gcc/config/riscv/riscv-vsetvl.cc
> @@ -3269,7 +3269,7 @@ pass_vsetvl::earliest_fusion (void)
> for (size_t i = 0; i < m_vector_manager->vector_exprs.length (); i++)
> {
> auto &expr = *m_vector_manager->vector_exprs[i];
> - if (expr.empty_p ())
> + if (expr.empty_p () || vsetvl_insn_p (expr.get_insn ()->rtl ()))
> continue;
> edge eg = INDEX_EDGE (m_vector_manager->vector_edge_list, ed);
> if (eg->src == ENTRY_BLOCK_PTR_FOR_FN (cfun)
>
