[2/2] RISC-V: Eliminate latter vsetvl when fused

The current vsetvl pass eliminates a vsetvl instruction when the previous
info is "available," but does not when "compatible."  This can lead to not
only redundancy, but also incorrect behaviors when the previous info happens
to be compatible with a later vector instruction, which ends of using the
vsetvl info that should have been eliminated, as is shown in the testcase.
This patch eliminates the vsetvl when the previous info is "compatible."

gcc/ChangeLog:

	* config/riscv/riscv-vsetvl.cc (pre_vsetvl::fuse_local_vsetvl_info):
	Delete vsetvl insn when `prev_info` is compatible

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/vsetvl/vsetvl_bug-4.c: New test.
---
 gcc/config/riscv/riscv-vsetvl.cc               |  3 +++
 .../gcc.target/riscv/rvv/vsetvl/vsetvl_bug-4.c | 18 ++++++++++++++++++
 2 files changed, 21 insertions(+)
 create mode 100644 gcc/testsuite/gcc.target/riscv/rvv/vsetvl/vsetvl_bug-4.c

An updated version has been submitted:
https://gcc.gnu.org/pipermail/gcc-patches/2024-September/662854.html

------------------------------------------------------------------
From:Bohan Lei <garthlei@linux.alibaba.com>
Send Time:2024 Sep. 11 (Wed.) 17:12
To:"gcc-patches"<gcc-patches@gcc.gnu.org>
Subject:[PATCH 2/2] RISC-V: Eliminate latter vsetvl when fused


The current vsetvl pass eliminates a vsetvl instruction when the previous
info is "available," but does not when "compatible."  This can lead to not
only redundancy, but also incorrect behaviors when the previous info happens
to be compatible with a later vector instruction, which ends of using the
vsetvl info that should have been eliminated, as is shown in the testcase.
This patch eliminates the vsetvl when the previous info is "compatible."

gcc/ChangeLog:

 * config/riscv/riscv-vsetvl.cc (pre_vsetvl::fuse_local_vsetvl_info):
 Delete vsetvl insn when `prev_info` is compatible

gcc/testsuite/ChangeLog:

 * gcc.target/riscv/rvv/vsetvl/vsetvl_bug-4.c: New test.
---
 gcc/config/riscv/riscv-vsetvl.cc               |  3 +++
 .../gcc.target/riscv/rvv/vsetvl/vsetvl_bug-4.c | 18 ++++++++++++++++++
 2 files changed, 21 insertions(+)
 create mode 100644 gcc/testsuite/gcc.target/riscv/rvv/vsetvl/vsetvl_bug-4.c

diff --git a/gcc/config/riscv/riscv-vsetvl.cc b/gcc/config/riscv/riscv-vsetvl.cc
index ce831685439..030ffbe2ebb 100644
--- a/gcc/config/riscv/riscv-vsetvl.cc
+++ b/gcc/config/riscv/riscv-vsetvl.cc
@@ -2796,6 +2796,9 @@ pre_vsetvl::fuse_local_vsetvl_info ()
         curr_info.dump (dump_file, "        ");
       }
     m_dem.merge (prev_info, curr_info);
+    if (!curr_info.vl_used_by_non_rvv_insn_p ()
+        && vsetvl_insn_p (curr_info.get_insn ()->rtl ()))
+      m_delete_list.safe_push (curr_info);
     if (curr_info.get_read_vl_insn ())
       prev_info.set_read_vl_insn (curr_info.get_read_vl_insn ());
     if (dump_file && (dump_flags & TDF_DETAILS))
diff --git a/gcc/testsuite/gcc.target/riscv/rvv/vsetvl/vsetvl_bug-4.c b/gcc/testsuite/gcc.target/riscv/rvv/vsetvl/vsetvl_bug-4.c
new file mode 100644
index 00000000000..faa0c8073d3
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/rvv/vsetvl/vsetvl_bug-4.c
@@ -0,0 +1,18 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gcv -mabi=lp64d -O2 -fno-schedule-insns -fdump-rtl-vsetvl-details" } */
+
+#include <riscv_vector.h>
+
+vuint16m1_t
+foo (vuint16m1_t a, vuint16m1_t b, size_t avl)
+{
+  size_t vl;
+  vuint16m1_t ret;
+  uint16_t c = __riscv_vmv_x_s_u16m1_u16(a);
+  vl = __riscv_vsetvl_e8mf2 (avl);
+  ret = __riscv_vadd_vx_u16m1 (a, c, avl);
+  ret = __riscv_vadd_vv_u16m1 (ret, a, vl);
+  return ret;
+}
+
+/* { dg-final { scan-rtl-dump "Eliminate insn" "vsetvl" } }  */

Could you CC to me ? I can't reply that patch directly.



juzhe.zhong@rivai.ai
 
From: Bohan Lei
Date: 2024-09-12 10:38
To: Bohan Lei
CC: gcc-patches; juzhe.zhong
Subject: RE: [PATCH 2/2] RISC-V: Eliminate latter vsetvl when fused
An updated version has been submitted:
https://gcc.gnu.org/pipermail/gcc-patches/2024-September/662854.html
 
------------------------------------------------------------------
From:Bohan Lei <garthlei@linux.alibaba.com>
Send Time:2024 Sep. 11 (Wed.) 17:12
To:"gcc-patches"<gcc-patches@gcc.gnu.org>
Subject:[PATCH 2/2] RISC-V: Eliminate latter vsetvl when fused
 
 
The current vsetvl pass eliminates a vsetvl instruction when the previous
info is "available," but does not when "compatible."  This can lead to not
only redundancy, but also incorrect behaviors when the previous info happens
to be compatible with a later vector instruction, which ends of using the
vsetvl info that should have been eliminated, as is shown in the testcase.
This patch eliminates the vsetvl when the previous info is "compatible."
 
gcc/ChangeLog:
 
* config/riscv/riscv-vsetvl.cc (pre_vsetvl::fuse_local_vsetvl_info):
Delete vsetvl insn when `prev_info` is compatible
 
gcc/testsuite/ChangeLog:
 
* gcc.target/riscv/rvv/vsetvl/vsetvl_bug-4.c: New test.
---
gcc/config/riscv/riscv-vsetvl.cc               |  3 +++
.../gcc.target/riscv/rvv/vsetvl/vsetvl_bug-4.c | 18 ++++++++++++++++++
2 files changed, 21 insertions(+)
create mode 100644 gcc/testsuite/gcc.target/riscv/rvv/vsetvl/vsetvl_bug-4.c
 
diff --git a/gcc/config/riscv/riscv-vsetvl.cc b/gcc/config/riscv/riscv-vsetvl.cc
index ce831685439..030ffbe2ebb 100644
--- a/gcc/config/riscv/riscv-vsetvl.cc
+++ b/gcc/config/riscv/riscv-vsetvl.cc
@@ -2796,6 +2796,9 @@ pre_vsetvl::fuse_local_vsetvl_info ()
        curr_info.dump (dump_file, "        ");
      }
    m_dem.merge (prev_info, curr_info);
+    if (!curr_info.vl_used_by_non_rvv_insn_p ()
+        && vsetvl_insn_p (curr_info.get_insn ()->rtl ()))
+      m_delete_list.safe_push (curr_info);
    if (curr_info.get_read_vl_insn ())
      prev_info.set_read_vl_insn (curr_info.get_read_vl_insn ());
    if (dump_file && (dump_flags & TDF_DETAILS))
diff --git a/gcc/testsuite/gcc.target/riscv/rvv/vsetvl/vsetvl_bug-4.c b/gcc/testsuite/gcc.target/riscv/rvv/vsetvl/vsetvl_bug-4.c
new file mode 100644
index 00000000000..faa0c8073d3
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/rvv/vsetvl/vsetvl_bug-4.c
@@ -0,0 +1,18 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gcv -mabi=lp64d -O2 -fno-schedule-insns -fdump-rtl-vsetvl-details" } */
+
+#include <riscv_vector.h>
+
+vuint16m1_t
+foo (vuint16m1_t a, vuint16m1_t b, size_t avl)
+{
+  size_t vl;
+  vuint16m1_t ret;
+  uint16_t c = __riscv_vmv_x_s_u16m1_u16(a);
+  vl = __riscv_vsetvl_e8mf2 (avl);
+  ret = __riscv_vadd_vx_u16m1 (a, c, avl);
+  ret = __riscv_vadd_vv_u16m1 (ret, a, vl);
+  return ret;
+}
+
+/* { dg-final { scan-rtl-dump "Eliminate insn" "vsetvl" } }  */