>> 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? Yes, the "source" these 2 pred_broadcast the same. However, they have different pseudos in their "dest" (operands[0]) The first one is 151, the second one is 152. And the result in these 2 pseudos are the same. The first pred_add use 151, the second pred_add use 152. CSE should do the job to eliminate the second pred_broadcast, but I am not sure whether CSE can propagate the 151 pseudo to the second pred_add ?? juzhe.zhong@rivai.ai From: Richard Biener Date: 2023-02-01 20:51 To: juzhe.zhong@rivai.ai CC: gcc-patches; kito.cheng; richard.sandiford; jeffreyalaw; apinski Subject: Re: Re: [PATCH] CPROP: Allow cprop optimization when the function has a single block 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 > > > > 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 SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg, Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman; HRB 36809 (AG Nuernberg)