[gcc(refs/vendors/riscv/heads/gcc-15-with-riscv-opts)] RISC-V: Leverage vaadd.vv for signed standard name avg_floor

[Jeff Law]

https://gcc.gnu.org/g:70e894e860d055e67883ebcae9e1497023d48515

commit 70e894e860d055e67883ebcae9e1497023d48515
Author: Pan Li <pan2.li@intel.com>
Date:   Tue May 27 09:53:56 2025 +0800

    RISC-V: Leverage vaadd.vv for signed standard name avg_floor
    
    The signed avg_floor totally match the sematics of fixed point
    rvv insn vaadd, within round down.  Thus, leverage it directly
    to implement the avf_floor.
    
    The spec of RVV is somehow not that clear about the difference
    between the float point and fixed point for the rounding that
    discard least-significant information.
    
    For float point which is not two's complement, the "discard
    least-significant information" indicates truncation round.  For
    example as below:
    
    * 3.5 -> 3
    * -2.3 -> -2
    
    For fixed point which is two's complement, the "discard
    least-significant information" indicates round down.  For
    example as below:
    
    * 3.5 -> 3
    * -2.3 -> -3
    
    And the vaadd takes the round down which is totally matching
    the sematics of the avf_floor.
    
    The below test suites are passed for this patch series.
    * The rv64gcv fully regression test.
    
    gcc/ChangeLog:
    
            * config/riscv/autovec.md (avg<v_double_trunc>3_floor): Add insn
            expand to leverage vaadd directly.
    
    Signed-off-by: Pan Li <pan2.li@intel.com>
    (cherry picked from commit f4456ea9e955b971573cdfebd1d10797fd30ad3a)

Diff:
---
 gcc/config/riscv/autovec.md | 19 ++++++-------------
 1 file changed, 6 insertions(+), 13 deletions(-)

diff --git a/gcc/config/riscv/autovec.md b/gcc/config/riscv/autovec.md
index 9e51e3ce6a30..a54f552a80ce 100644
--- a/gcc/config/riscv/autovec.md
+++ b/gcc/config/riscv/autovec.md
@@ -2491,19 +2491,12 @@
       (sign_extend:VWEXTI
        (match_operand:<V_DOUBLE_TRUNC> 2 "register_operand"))))))]
   "TARGET_VECTOR"
-{
-  /* First emit a widening addition.  */
-  rtx tmp1 = gen_reg_rtx (<MODE>mode);
-  rtx ops1[] = {tmp1, operands[1], operands[2]};
-  insn_code icode = code_for_pred_dual_widen (PLUS, SIGN_EXTEND, <MODE>mode);
-  riscv_vector::emit_vlmax_insn (icode, riscv_vector::BINARY_OP, ops1);
-
-  /* Then a narrowing shift.  */
-  rtx ops2[] = {operands[0], tmp1, const1_rtx};
-  icode = code_for_pred_narrow_scalar (ASHIFTRT, <MODE>mode);
-  riscv_vector::emit_vlmax_insn (icode, riscv_vector::BINARY_OP, ops2);
-  DONE;
-})
+  {
+    insn_code icode = code_for_pred (UNSPEC_VAADD, <V_DOUBLE_TRUNC>mode);
+    riscv_vector::emit_vlmax_insn (icode, riscv_vector::BINARY_OP_VXRM_RDN, operands);
+    DONE;
+  }
+)
 
 (define_expand "avg<v_double_trunc>3_ceil"
  [(set (match_operand:<V_DOUBLE_TRUNC> 0 "register_operand")