[gcc r14-11563] RISC-V: Fix vl_used_by_non_rvv_insn logic of vsetvl pass

[Kito Cheng via Gcc-cvs]

https://gcc.gnu.org/g:94b774c5c1cd67608c31d593167996351e952cea

commit r14-11563-g94b774c5c1cd67608c31d593167996351e952cea
Author: garthlei <garth...@linux.alibaba.com>
Date:   Wed Sep 11 17:09:37 2024 +0800

    RISC-V: Fix vl_used_by_non_rvv_insn logic of vsetvl pass
    
    This patch fixes a bug in the current vsetvl pass.  The current pass uses
    `m_vl` to determine whether the dest operand has been used by non-RVV
    instructions.  However, `m_vl` may have been modified as a result of an
    `update_avl` call, and thus would be no longer the dest operand of the
    original instruction.  This can lead to incorrect vsetvl eliminations, as is
    shown in the testcase.  In this patch, we create a `dest_vl` variable for
    this scenerio.
    
    gcc/ChangeLog:
    
            * config/riscv/riscv-vsetvl.cc: Use `dest_vl` for dest VL operand
    
    gcc/testsuite/ChangeLog:
    
            * gcc.target/riscv/rvv/vsetvl/vsetvl_bug-3.c: New test.

Diff:
---
 gcc/config/riscv/riscv-vsetvl.cc                        | 16 +++++++++++-----
 .../gcc.target/riscv/rvv/vsetvl/vsetvl_bug-3.c          | 17 +++++++++++++++++
 2 files changed, 28 insertions(+), 5 deletions(-)

diff --git a/gcc/config/riscv/riscv-vsetvl.cc b/gcc/config/riscv/riscv-vsetvl.cc
index 96cd82756cf8..49702a5c6838 100644
--- a/gcc/config/riscv/riscv-vsetvl.cc
+++ b/gcc/config/riscv/riscv-vsetvl.cc
@@ -1004,6 +1004,9 @@ public:
 
   void parse_insn (insn_info *insn)
   {
+    /* The VL dest of the insn */
+    rtx dest_vl = NULL_RTX;
+
     m_insn = insn;
     m_bb = insn->bb ();
     /* Return if it is debug insn for the consistency with optimize == 0.  */
@@ -1037,7 +1040,10 @@ public:
     if (m_avl)
       {
        if (vsetvl_insn_p (insn->rtl ()) || has_vlmax_avl ())
-         m_vl = ::get_vl (insn->rtl ());
+         {
+           m_vl = ::get_vl (insn->rtl ());
+           dest_vl = m_vl;
+         }
 
        if (has_nonvlmax_reg_avl ())
          m_avl_def = find_access (insn->uses (), REGNO (m_avl))->def ();
@@ -1134,22 +1140,22 @@ public:
       }
 
     /* Determine if dest operand(vl) has been used by non-RVV instructions.  */
-    if (has_vl ())
+    if (dest_vl)
       {
        const hash_set<use_info *> vl_uses
-         = get_all_real_uses (get_insn (), REGNO (get_vl ()));
+         = get_all_real_uses (get_insn (), REGNO (dest_vl));
        for (use_info *use : vl_uses)
          {
            gcc_assert (use->insn ()->is_real ());
            rtx_insn *rinsn = use->insn ()->rtl ();
            if (!has_vl_op (rinsn)
-               || count_regno_occurrences (rinsn, REGNO (get_vl ())) != 1)
+               || count_regno_occurrences (rinsn, REGNO (dest_vl)) != 1)
              {
                m_vl_used_by_non_rvv_insn = true;
                break;
              }
            rtx avl = ::get_avl (rinsn);
-           if (!avl || !REG_P (avl) || REGNO (get_vl ()) != REGNO (avl))
+           if (!avl || !REG_P (avl) || REGNO (dest_vl) != REGNO (avl))
              {
                m_vl_used_by_non_rvv_insn = true;
                break;
diff --git a/gcc/testsuite/gcc.target/riscv/rvv/vsetvl/vsetvl_bug-3.c 
b/gcc/testsuite/gcc.target/riscv/rvv/vsetvl/vsetvl_bug-3.c
new file mode 100644
index 000000000000..3acbc739d4dd
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/rvv/vsetvl/vsetvl_bug-3.c
@@ -0,0 +1,17 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv32gcv -mabi=ilp32d -O2 -fdump-rtl-vsetvl-details" } 
*/
+
+#include "riscv_vector.h"
+
+uint64_t a[2], b[2];
+
+void
+foo ()
+{
+  size_t vl = __riscv_vsetvl_e64m1 (2);
+  vuint64m1_t vx = __riscv_vle64_v_u64m1 (a, vl);
+  vx = __riscv_vslide1down_vx_u64m1 (vx, 0xffffffffull, vl);
+  __riscv_vse64_v_u64m1 (b, vx, vl);
+}
+
+/* { dg-final { scan-rtl-dump-not "Eliminate insn" "vsetvl" } }  */