Re: [PATCH 3/5] [RISC-V] Generate Zicond instruction for select pattern with condition eq or neq to 0

[Jeff Law via Gcc-patches]

On 7/19/23 04:11, Xiao Zeng wrote:
This patch completes the recognition of Zicond when the select pattern
with condition eq or neq to 0 (using equality as an example), namely:
[ ... ]
I've committed the attached patch which implements a simple cost model 
for using Zicond to implement conditional moves.

I've changed it to give the proper cost (COSTS_N_INSNS (1) and removed 
the extraneous GET_CODE (object) tests adjusted the ChangeLog a bit and 
pushed it to the trunk.

Thanks!

Jeffcommit 5b501863ac7da57858fdd464dfb7a776143f22a2
Author: Xiao Zeng <zengx...@eswincomputing.com>
Date:   Wed Aug 2 00:17:12 2023 -0600

    [PATCH 3/5] [RISC-V] Cost model for Zicond.
    
    This patch implements a reasonable cost model for using Zicond to
    implement conditional moves.  Essentially the Zicond insns are always
    COSTS_N_INSNS (1).
    
    Note there is still a problem with the costing model in general that
    results in failure to if-convert as often as we should.  In simplest
    terms the insn costing model sums the cost of the SET_SRC and the
    cost of the SET_DEST.  Thus the conditional move is considered twice
    as costly as it should be.  That will have to be addressed separately.
    
    gcc/
            * config/riscv/riscv.cc (riscv_rtx_costs): Add costing for
            using Zicond to implement some conditional moves.

diff --git a/gcc/config/riscv/riscv.cc b/gcc/config/riscv/riscv.cc
index 8c474503080..785e09c76ce 100644
--- a/gcc/config/riscv/riscv.cc
+++ b/gcc/config/riscv/riscv.cc
@@ -2518,6 +2518,20 @@ riscv_rtx_costs (rtx x, machine_mode mode, int 
outer_code, int opno ATTRIBUTE_UN
          *total = COSTS_N_INSNS (1);
          return true;
        }
+      else if (TARGET_ZICOND
+              && outer_code == SET
+              && ((GET_CODE (XEXP (x, 1)) == REG
+                   && XEXP (x, 2) == CONST0_RTX (GET_MODE (XEXP (x, 1))))
+                  || (GET_CODE (XEXP (x, 2)) == REG
+                      && XEXP (x, 1) == CONST0_RTX (GET_MODE (XEXP (x, 2))))
+                  || (GET_CODE (XEXP (x, 1)) == REG
+                      && rtx_equal_p (XEXP (x, 1), XEXP (XEXP (x, 0), 0)))
+                  || (GET_CODE (XEXP (x, 1)) == REG
+                      && rtx_equal_p (XEXP (x, 2), XEXP (XEXP (x, 0), 0)))))
+       {
+         *total = COSTS_N_INSNS (1);
+         return true;
+       }
       else if (LABEL_REF_P (XEXP (x, 1)) && XEXP (x, 2) == pc_rtx)
        {
          if (equality_operator (XEXP (x, 0), mode)