[PATCH] RISC-V: Disable AVL propagation of vrgather instruction

[PATCH] RISC-V: Disable AVL propagation of vrgather instruction

[Juzhe-Zhong]

This patch fixes following FAILs in zvl1024b of both RV32/RV64:

FAIL: gcc.c-torture/execute/990128-1.c   -O2  execution test
FAIL: gcc.c-torture/execute/990128-1.c   -O2 -flto -fno-use-linker-plugin -flto-partition=none  execution test
FAIL: gcc.c-torture/execute/990128-1.c   -O2 -flto -fuse-linker-plugin -fno-fat-lto-objects  execution test
FAIL: gcc.c-torture/execute/990128-1.c   -O3 -fomit-frame-pointer -funroll-loops -fpeel-loops -ftracer -finline-functions  execution test
FAIL: gcc.c-torture/execute/990128-1.c   -O3 -g  execution test
FAIL: gcc.dg/torture/pr58955-2.c   -O3 -fomit-frame-pointer -funroll-loops -fpeel-loops -ftracer -finline-functions  execution test

The root case can be simpliy described in this following small case:

https://godbolt.org/z/7GaxbEGzG

#include "riscv_vector.h"

typedef int64_t v1024b __attribute__ ((vector_size (128)));

void foo (void *out, void *in, int64_t a, int64_t b)
{
  v1024b v = {a,a,a,a,a,a,a,a,a,a,a,a,a,a,a,a};
  v1024b v2 = {b,b,b,b,b,b,b,b,b,b,b,b,b,b,b,b};
  v1024b index = *(v1024b*)in;
  v1024b v3 = __builtin_shuffle (v, v2, index);
  __riscv_vse64_v_i64m1 (out, (vint64m1_t)v3, 10);
}

Incorrect ASM:

foo:
        li      a5,31
        vsetivli        zero,10,e64,m1,ta,mu
        vmv.v.x v2,a5
        vl1re64.v       v1,0(a1)
        vmv.v.x v4,a2
        vand.vv v1,v1,v2
        vmv.v.x v3,a3
        vmsgeu.vi       v0,v1,16
        vrgather.vv     v2,v4,v1       --> AVL = VLMAX according to codes.
        vadd.vi v1,v1,-16
        vrgather.vv     v2,v3,v1,v0.t  --> AVL = VLMAX according to codes.
        vse64.v v2,0(a0)               --> AVL = 10 according to codes.
        ret

For vrgather dest, source, index instruction, when index may has the value > the following store AVL
that is index value > 10.  In this situation, the codes above will end up with:

The source vector of vrgather has undefined value on index >= AVL (which is 10 in this case).

So disable AVL propagation for vrgather instruction.


	PR target/112599

gcc/ChangeLog:

	* config/riscv/riscv-avlprop.cc (alv_can_be_propagated_p): New function.
	(vlmax_ta_p): Disable vrgather AVL propagation.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/autovec/pr112599-1.c: New test.

---
 gcc/config/riscv/riscv-avlprop.cc               | 13 ++++++++++++-
 .../gcc.target/riscv/rvv/autovec/pr112599-1.c   | 17 +++++++++++++++++
 2 files changed, 29 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gcc.target/riscv/rvv/autovec/pr112599-1.c

diff --git a/gcc/config/riscv/riscv-avlprop.cc b/gcc/config/riscv/riscv-avlprop.cc
index 1f6ba405342..68b9af07d99 100644
--- a/gcc/config/riscv/riscv-avlprop.cc
+++ b/gcc/config/riscv/riscv-avlprop.cc
@@ -104,10 +104,21 @@ avlprop_type_to_str (enum avlprop_type type)
     }
 }
 
+/* Return true if the AVL of the INSN can be propagated.  */
+static bool
+alv_can_be_propagated_p (rtx_insn *rinsn)
+{
+  /* The index of "vrgather dest, source, index" may pick up the
+     element which has index >= AVL, so we can't strip the elements
+     that has index >= AVL of source register.  */
+  return get_attr_type (rinsn) != TYPE_VGATHER;
+}
+
 static bool
 vlmax_ta_p (rtx_insn *rinsn)
 {
-  return vlmax_avl_type_p (rinsn) && tail_agnostic_p (rinsn);
+  return vlmax_avl_type_p (rinsn) && tail_agnostic_p (rinsn)
+	 && alv_can_be_propagated_p (rinsn);
 }
 
 static machine_mode
diff --git a/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr112599-1.c b/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr112599-1.c
new file mode 100644
index 00000000000..911b6922b4a
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr112599-1.c
@@ -0,0 +1,17 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gcv_zvfh_zfh_zvl1024b -mabi=lp64d -O3 --param=riscv-autovec-preference=fixed-vlmax" } */
+
+#include "riscv_vector.h"
+
+typedef int64_t v1024b __attribute__ ((vector_size (128)));
+
+void foo (void *out, void *in, int64_t a, int64_t b)
+{
+  v1024b v = {a,a,a,a,a,a,a,a,a,a,a,a,a,a,a,a};
+  v1024b v2 = {b,b,b,b,b,b,b,b,b,b,b,b,b,b,b,b};
+  v1024b index = *(v1024b*)in;
+  v1024b v3 = __builtin_shuffle (v, v2, index);
+  __riscv_vse64_v_i64m1 (out, (vint64m1_t)v3, 10);
+}
+
+/* { dg-final { scan-assembler {vsetivli\s+zero,\s*16} } } */
-- 
2.36.3

Re: [PATCH] RISC-V: Disable AVL propagation of vrgather instruction

[Robin Dapp]

I was just about to post a similar-ish patch that fixes pr65518.c
but you were faster ;)

Therefore LGTM.  You can add PR/target 112670.

Regards
 Robin

Re: Re: [PATCH] RISC-V: Disable AVL propagation of vrgather instruction

[juzhe.zhong]

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Oh. You mean this patch also fixes FLTO failed case ?



juzhe.zhong@rivai.ai
 
From: Robin Dapp
Date: 2023-11-23 19:55
To: Juzhe-Zhong; gcc-patches
CC: rdapp.gcc; kito.cheng; kito.cheng; jeffreyalaw
Subject: Re: [PATCH] RISC-V: Disable AVL propagation of vrgather instruction
I was just about to post a similar-ish patch that fixes pr65518.c
but you were faster ;)
 
Therefore LGTM.  You can add PR/target 112670.
 
Regards
Robin
 

Re: [PATCH] RISC-V: Disable AVL propagation of vrgather instruction

[Robin Dapp]

> Oh. You mean this patch also fixes FLTO failed case ?

Yes, it's the same issue.  There we have a fixed vl (known via LTO)
that is being propagated "into" gathers and we end up missing
gather elements.

Regards
 Robin

Re: Re: [PATCH] RISC-V: Disable AVL propagation of vrgather instruction

[juzhe.zhong]

[-- Attachment #1: Type: text/plain, Size: 729 bytes --]

Thanks Robin.

I have sent V2:
https://gcc.gnu.org/pipermail/gcc-patches/2023-November/637921.html 
with adding PR/target 112670

Could you commit it for me ?

I am sorry that make you doing redundant work.
I didn't realize they are same issue :)


juzhe.zhong@rivai.ai
 
From: Robin Dapp
Date: 2023-11-23 19:58
To: juzhe.zhong@rivai.ai; gcc-patches
CC: rdapp.gcc; kito.cheng; Kito.cheng; jeffreyalaw
Subject: Re: [PATCH] RISC-V: Disable AVL propagation of vrgather instruction
> Oh. You mean this patch also fixes FLTO failed case ?
 
Yes, it's the same issue.  There we have a fixed vl (known via LTO)
that is being propagated "into" gathers and we end up missing
gather elements.
 
Regards
Robin