[gcc(refs/vendors/riscv/heads/gcc-15-with-riscv-opts)] RISC-V: Adjust tt-ascalon-d8 branch cost

[Jeff Law]

https://gcc.gnu.org/g:a23e0cd280d07690ba4be5dc9f99a53897d36c95

commit a23e0cd280d07690ba4be5dc9f99a53897d36c95
Author: Anton Blanchard <antonb@tenstorrent.com>
Date:   Mon Sep 8 07:36:39 2025 -0600

    RISC-V: Adjust tt-ascalon-d8 branch cost
    
    If-conversion isn't being applied to this nbench code:
    
     #include <stdint.h>
     #define INTERNAL_FPF_PRECISION 4
     typedef uint16_t u16;
    
     void ShiftMantLeft1(u16 *carry, u16 *mantissa)
     {
             int i;
             int new_carry;
             u16 accum;
    
             for(i=INTERNAL_FPF_PRECISION-1;i>=0;i--)
             {       accum=mantissa[i];
                     new_carry=accum & 0x8000;
                     accum=accum<<1;
                     if(*carry)
                             accum|=1;
                     *carry=new_carry;
                     mantissa[i]=accum;
             }
             return;
     }
    
    Bumping branch_cost from 3 to 4 triggers if-conversion, improving the
    nbench FP EMULATION result on Ascalon significantly. There's a risk
    that more aggressive use of conditional zero instructions will negatively
    impact workloads that predict well, but we haven't seen anything obvious.
    
    gcc/ChangeLog:
            * config/riscv/riscv.cc (tt_ascalon_d8_tune_info): Increase branch_cost
            from 3 to 4.
    
    (cherry picked from commit 11171cb98098e0a6438a5c2f964f5d45f2127b76)

Diff:
---
 gcc/config/riscv/riscv.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/gcc/config/riscv/riscv.cc b/gcc/config/riscv/riscv.cc
index 2dcc5b4fd86c..060b15fcdc6f 100644
--- a/gcc/config/riscv/riscv.cc
+++ b/gcc/config/riscv/riscv.cc
@@ -659,7 +659,7 @@ static const struct riscv_tune_param tt_ascalon_d8_tune_info = {
   {COSTS_N_INSNS (3), COSTS_N_INSNS (3)},	/* int_mul */
   {COSTS_N_INSNS (13), COSTS_N_INSNS (13)},	/* int_div */
   8,						/* issue_rate */
-  3,						/* branch_cost */
+  4,						/* branch_cost */
   4,						/* memory_cost */
   4,						/* fmv_cost */
   false,					/* slow_unaligned_access */