[PATCH v3] target/riscv: Use env_archcpu for better performance

["Richard W.M. Jones" <rjones@redhat.com>]

RISCV_CPU(cs) uses a checked cast.  When QOM cast debugging is enabled
this adds about 5% total overhead when emulating RV64 on x86-64 host.

Using a RISC-V guest with 16 vCPUs, 16 GB of guest RAM, virtio-blk
disk.  The guest has a copy of the qemu source tree.  The test
involves compiling the qemu source tree with 'make clean; time make -j16'.

Before making this change the compile step took 449 & 447 seconds over
two consecutive runs.

After making this change: 428 & 421 seconds.

The saving is over 5%.

Thanks: Paolo Bonzini
Thanks: Philippe Mathieu-Daudé
Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
---
 target/riscv/cpu_helper.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
index 3a02079290..8c28241c18 100644
--- a/target/riscv/cpu_helper.c
+++ b/target/riscv/cpu_helper.c
@@ -65,8 +65,7 @@ int riscv_cpu_mmu_index(CPURISCVState *env, bool ifetch)
 void cpu_get_tb_cpu_state(CPURISCVState *env, vaddr *pc,
                           uint64_t *cs_base, uint32_t *pflags)
 {
-    CPUState *cs = env_cpu(env);
-    RISCVCPU *cpu = RISCV_CPU(cs);
+    RISCVCPU *cpu = env_archcpu(env);
     RISCVExtStatus fs, vs;
     uint32_t flags = 0;
 
-- 
2.41.0