From: Richard Biener <rguenther@suse.de>
To: "juzhe.zhong@rivai.ai" <juzhe.zhong@rivai.ai>
Cc: gcc-patches <gcc-patches@gcc.gnu.org>,
"kito.cheng" <kito.cheng@gmail.com>,
"richard.sandiford" <richard.sandiford@arm.com>,
jeffreyalaw <jeffreyalaw@gmail.com>,
apinski <apinski@marvell.com>
Subject: Re: Re: [PATCH] CPROP: Allow cprop optimization when the function has a single block
Date: Wed, 1 Feb 2023 12:51:45 +0000 (UTC) [thread overview]
Message-ID: <nycvar.YFH.7.77.849.2302011250410.6551@jbgna.fhfr.qr> (raw)
In-Reply-To: <B6B0AA4AB81FC518+2023020120465949988069@rivai.ai>
On Wed, 1 Feb 2023, juzhe.zhong@rivai.ai wrote:
> I don't known whether CSE do the job. What I saw is CPROP do the optimization when we have more than 1 block.
>
> This the RTL dump before CPROP:
>
> (insn 19 18 20 4 (set (reg:VNx1DI 151)
> (if_then_else:VNx1DI (unspec:VNx1BI [
> (const_vector:VNx1BI repeat [
> (const_int 1 [0x1])
> ])
> (const_int 4 [0x4])
> (const_int 2 [0x2]) repeated x2
> (const_int 0 [0])
> (reg:SI 66 vl)
> (reg:SI 67 vtype)
> ] UNSPEC_VPREDICATE)
> (vec_duplicate:VNx1DI (reg/v:DI 148 [ x ]))
> (unspec:VNx1DI [
> (const_int 0 [0])
> ] UNSPEC_VUNDEF))) "rvv.c":22:23 695 {pred_broadcastvnx1di}
> (nil))
> (insn 20 19 21 4 (set (reg/v:VNx1DI 139 [ v3 ])
> (if_then_else:VNx1DI (unspec:VNx1BI [
> (const_vector:VNx1BI repeat [
> (const_int 1 [0x1])
> ])
> (const_int 4 [0x4])
> (const_int 2 [0x2]) repeated x2
> (const_int 0 [0])
> (reg:SI 66 vl)
> (reg:SI 67 vtype)
> ] UNSPEC_VPREDICATE)
> (plus:VNx1DI (reg/v:VNx1DI 138 [ v2 ])
> (reg:VNx1DI 151))
> (unspec:VNx1DI [
> (const_int 0 [0])
> ] UNSPEC_VUNDEF))) "rvv.c":22:23 1528 {pred_addvnx1di}
> (expr_list:REG_DEAD (reg:VNx1DI 151)
> (nil)))
> (insn 21 20 22 4 (set (reg:VNx1DI 152)
> (if_then_else:VNx1DI (unspec:VNx1BI [
> (const_vector:VNx1BI repeat [
> (const_int 1 [0x1])
> ])
> (const_int 4 [0x4])
> (const_int 2 [0x2]) repeated x2
> (const_int 0 [0])
> (reg:SI 66 vl)
> (reg:SI 67 vtype)
> ] UNSPEC_VPREDICATE)
> (vec_duplicate:VNx1DI (reg/v:DI 148 [ x ]))
> (unspec:VNx1DI [
> (const_int 0 [0])
> ] UNSPEC_VUNDEF))) "rvv.c":23:23 695 {pred_broadcastvnx1di}
> (nil))
> (insn 22 21 23 4 (set (reg/v:VNx1DI 140 [ v4 ])
> (if_then_else:VNx1DI (unspec:VNx1BI [
> (const_vector:VNx1BI repeat [
> (const_int 1 [0x1])
> ])
> (const_int 4 [0x4])
> (const_int 0 [0])
> (const_int 2 [0x2])
> (const_int 0 [0])
> (reg:SI 66 vl)
> (reg:SI 67 vtype)
> ] UNSPEC_VPREDICATE)
> (plus:VNx1DI (reg/v:VNx1DI 138 [ v2 ])
> (reg:VNx1DI 152))
> (reg/v:VNx1DI 139 [ v3 ]))) "rvv.c":23:23 1528 {pred_addvnx1di}
> (expr_list:REG_DEAD (reg:VNx1DI 152)
> (expr_list:REG_DEAD (reg/v:VNx1DI 139 [ v3 ])
> (expr_list:REG_DEAD (reg/v:VNx1DI 138 [ v2 ])
> (nil)))))
>
> After CRPOP:
> (insn 15 14 16 4 (set (reg:VNx1DI 147)
> (if_then_else:VNx1DI (unspec:VNx1BI [
> (const_vector:VNx1BI repeat [
> (const_int 1 [0x1])
> ])
> (const_int 4 [0x4])
> (const_int 2 [0x2]) repeated x2
> (const_int 0 [0])
> (reg:SI 66 vl)
> (reg:SI 67 vtype)
> ] UNSPEC_VPREDICATE)
> (vec_duplicate:VNx1DI (reg/v:DI 143 [ x ]))
> (unspec:VNx1DI [
> (const_int 0 [0])
> ] UNSPEC_VUNDEF))) "rvv.c":11:23 695 {pred_broadcastvnx1di}
> (nil))
> (insn 16 15 18 4 (set (reg/v:VNx1DI 139 [ v3 ])
> (if_then_else:VNx1DI (unspec:VNx1BI [
> (const_vector:VNx1BI repeat [
> (const_int 1 [0x1])
> ])
> (const_int 4 [0x4])
> (const_int 2 [0x2]) repeated x2
> (const_int 0 [0])
> (reg:SI 66 vl)
> (reg:SI 67 vtype)
> ] UNSPEC_VPREDICATE)
> (plus:VNx1DI (reg/v:VNx1DI 138 [ v2 ])
> (reg:VNx1DI 147))
> (unspec:VNx1DI [
> (const_int 0 [0])
> ] UNSPEC_VUNDEF))) "rvv.c":11:23 1528 {pred_addvnx1di}
> (expr_list:REG_DEAD (reg:VNx1DI 147)
> (expr_list:REG_DEAD (reg/v:VNx1DI 138 [ v2 ])
> (nil))))
> (insn 18 16 19 4 (set (reg/v:VNx1DI 140 [ v4 ])
> (if_then_else:VNx1DI (unspec:VNx1BI [
> (const_vector:VNx1BI repeat [
> (const_int 1 [0x1])
> ])
> (const_int 4 [0x4])
> (const_int 2 [0x2]) repeated x2
> (const_int 0 [0])
> (reg:SI 66 vl)
> (reg:SI 67 vtype)
> ] UNSPEC_VPREDICATE)
> (plus:VNx1DI (reg/v:VNx1DI 139 [ v3 ])
> (reg:VNx1DI 147))
> (unspec:VNx1DI [
> (const_int 0 [0])
> ] UNSPEC_VUNDEF))) "rvv.c":12:23 1528 {pred_addvnx1di}
> (expr_list:REG_DEAD (reg:VNx1DI 148)
> (expr_list:REG_DEAD (reg/v:VNx1DI 139 [ v3 ])
> (nil))))
>
> You can see CPROP remove the second the "pred_broadcast" instruction and propagate the result to the second "pred_add" instruction?
I see loads of UNSPECs, that might explain why some passes do something
and some not. That said, not sure what exactly CPROP does, the two
pred_broadcast insns look exactly the same so CSE should CSE them?
>
>
> juzhe.zhong@rivai.ai
>
> From: Richard Biener
> Date: 2023-02-01 20:40
> To: Ju-Zhe Zhong
> CC: gcc-patches; kito.cheng; richard.sandiford; jeffreyalaw; apinski
> Subject: Re: [PATCH] CPROP: Allow cprop optimization when the function has a single block
> On Wed, 1 Feb 2023, juzhe.zhong@rivai.ai wrote:
>
> > From: Ju-Zhe Zhong <juzhe.zhong@rivai.ai>
> >
> > Hi, this patch is present for GCC 14 since I understand it's not appropriate
> > to land it in GCC 13.
> >
> > NUM_FIXED_BLOCKS = 2 since GCC define each function has aleast 2 blocks
> > one is entry block, the other is exit block.
> > So according this code, the function will not do cprop optimization when
> > there is only exactly one single block.
>
> cprop / GCSE are global dataflow problems, there's "nothing" to do for
> a single block, the local problem plus its application isn't considered
> but probably left for CSE.
>
> Why does CSE not perform the desired transform?
>
> > I am not sure whether it's correct to fix it like this.
> > Can anyone tell me why forbid cprop optimization if the function only has s
> > single block ?
> >
> > Let's take a look at these 2 examples of RVV intrinsics:
> > 1. void f1 (void * in, void *out, int64_t x, int n)
> > {
> > vint64m1_t v = __riscv_vle64_v_i64m1 (in + 1, 4);
> > vint64m1_t v2 = __riscv_vle64_v_i64m1_tu (v, in + 2, 4);
> > vint64m1_t v3 = __riscv_vadd_vx_i64m1 (v2, x, 4);
> > vint64m1_t v4 = __riscv_vadd_vx_i64m1 (v3, x, 4);
> > __riscv_vse64_v_i64m1 (out + 2, v4, 4);
> > }
> >
> > asm:
> > addi sp,sp,-16
> > sw a2,8(sp)
> > sw a3,12(sp)
> > sw a2,0(sp)
> > sw a3,4(sp)
> > addi a5,a0,1
> > vsetivli zero,4,e64,m1,ta,ma
> > addi a0,a0,2
> > vle64.v v24,0(a5)
> > addi a5,sp,8
> > vlse64.v v27,0(a5),zero
> > addi a1,a1,2
> > vsetvli zero,zero,e64,m1,tu,ma
> > vle64.v v24,0(a0)
> > vsetvli zero,zero,e64,m1,ta,ma
> > vlse64.v v25,0(sp),zero
> > vadd.vv v26,v24,v27
> > vadd.vv v24,v26,v25
> > vse64.v v24,0(a1)
> > addi sp,sp,16
> > jr ra
> > you can see here there are 2 vlse64.v instructions that broadcast the scalar value "x"
> > GCC fail to eliminate the second vlse64.v instruction since GCC doesn't do the cprop
> > optimization (the function only has 1 single block). It can be optimized if we apply
> > this patch.
> >
> > 2. void f1 (void * in, void *out, int64_t x, int n)
> > {
> > if (n) {
> > vint64m1_t v = __riscv_vle64_v_i64m1 (in + 1, 4);
> > vint64m1_t v2 = __riscv_vle64_v_i64m1_tu (v, in + 2, 4);
> > vint64m1_t v3 = __riscv_vadd_vx_i64m1 (v2, x, 4);
> > vint64m1_t v4 = __riscv_vadd_vx_i64m1 (v3, x, 4);
> > __riscv_vse64_v_i64m1 (out + 2, v4, 4);
> > }
> > }
> >
> > asm:
> > f1:
> > vsetivli zero,4,e64,m1,ta,ma
> > beq a4,zero,.L7
> > addi sp,sp,-16
> > sw a2,8(sp)
> > sw a3,12(sp)
> > addi a5,a0,1
> > vle64.v v24,0(a5)
> > addi a0,a0,2
> > addi a5,sp,8
> > vlse64.v v25,0(a5),zero
> > addi a1,a1,2
> > vsetvli zero,zero,e64,m1,tu,ma
> > vle64.v v24,0(a0)
> > vadd.vv v26,v24,v25
> > vadd.vv v24,v26,v25
> > vse64.v v24,0(a1)
> > addi sp,sp,16
> > jr ra
> > .L7:
> > ret
> >
> > Here, if we add if (n) condition here, the program will end up with more than 1 block.
> > So GCC will do the cprop optimization and the second vlse64.v instruction is eliminated.
> >
> > I am not sure whether this patch is correct.
> > Can anyone help me with that ?
> > Thanks.
> >
> >
> > gcc/ChangeLog:
> >
> > * cprop.cc (one_cprop_pass): Remove +1.
> >
> > ---
> > gcc/cprop.cc | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/gcc/cprop.cc b/gcc/cprop.cc
> > index 6ec0bda4a24..615bc5078b6 100644
> > --- a/gcc/cprop.cc
> > +++ b/gcc/cprop.cc
> > @@ -1749,7 +1749,7 @@ one_cprop_pass (void)
> > int changed = 0;
> >
> > /* Return if there's nothing to do, or it is too expensive. */
> > - if (n_basic_blocks_for_fn (cfun) <= NUM_FIXED_BLOCKS + 1
> > + if (n_basic_blocks_for_fn (cfun) <= NUM_FIXED_BLOCKS
> > || gcse_or_cprop_is_too_expensive (_ ("const/copy propagation disabled")))
> > return 0;
> >
> >
>
>
--
Richard Biener <rguenther@suse.de>
SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg,
Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman;
HRB 36809 (AG Nuernberg)
next prev parent reply other threads:[~2023-02-01 12:51 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-01 12:24 juzhe.zhong
2023-02-01 12:40 ` Richard Biener
2023-02-01 12:47 ` juzhe.zhong
2023-02-01 12:51 ` Richard Biener [this message]
2023-02-01 12:56 ` juzhe.zhong
[not found] ` <0CEDD257-703F-4ED3-B927-C21279557CE6@gmail.com>
2023-02-02 1:49 ` juzhe.zhong
2023-02-02 12:26 ` Richard Biener
2023-02-02 12:35 ` juzhe.zhong
2023-02-02 14:36 ` Jeff Law
2023-02-02 14:43 ` juzhe.zhong
2023-02-02 15:18 ` Kito Cheng
2023-02-02 14:36 ` Jeff Law
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