[Qemu-devel] [PATCH 4/4] target/arm: Rely on hflags correct in cpu_get_tb_cpu_state

[Richard Henderson <richard.henderson@linaro.org>]

This is the payoff.

>From perf record -g data of ubuntu 18 boot and shutdown:

BEFORE:

-   23.02%     2.82%  qemu-system-aar  [.] helper_lookup_tb_ptr
   - 20.22% helper_lookup_tb_ptr
      + 10.05% tb_htable_lookup
      - 9.13% cpu_get_tb_cpu_state
           3.20% aa64_va_parameters_both
           0.55% fp_exception_el

-   11.66%     4.74%  qemu-system-aar  [.] cpu_get_tb_cpu_state
   - 6.96% cpu_get_tb_cpu_state
        3.63% aa64_va_parameters_both
        0.60% fp_exception_el
        0.53% sve_exception_el

AFTER:

-   16.40%     3.40%  qemu-system-aar  [.] helper_lookup_tb_ptr
   - 13.03% helper_lookup_tb_ptr
      + 11.19% tb_htable_lookup
        0.55% cpu_get_tb_cpu_state

     0.98%     0.71%  qemu-system-aar  [.] cpu_get_tb_cpu_state

     0.87%     0.24%  qemu-system-aar  [.] rebuild_hflags_a64

Before, helper_lookup_tb_ptr is the second hottest function in the
application, consuming almost a quarter of the runtime.  Within the
entire execution, cpu_get_tb_cpu_state consumes about 12%.

After, helper_lookup_tb_ptr has dropped to the fourth hottest function,
with consumption dropping to a sixth of the runtime.  Within the
entire execution, cpu_get_tb_cpu_state has dropped below 1%, and the
supporting function to rebuild hflags also consumes about 1%.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 target/arm/helper.c | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/target/arm/helper.c b/target/arm/helper.c
index 3c8724883d..1bdb87267e 100644
--- a/target/arm/helper.c
+++ b/target/arm/helper.c
@@ -13894,21 +13894,16 @@ void HELPER(rebuild_hflags_a64)(CPUARMState *env, uint32_t el)
 void cpu_get_tb_cpu_state(CPUARMState *env, target_ulong *pc,
                           target_ulong *cs_base, uint32_t *pflags)
 {
-    int current_el = arm_current_el(env);
-    uint32_t flags;
+    uint32_t flags = env->hflags;
     uint32_t pstate_for_ss;
 
     *cs_base = 0;
-    if (is_a64(env)) {
+    if (FIELD_EX32(flags, TBFLAG_ANY, AARCH64_STATE)) {
         *pc = env->pc;
-        flags = rebuild_hflags_a64(env, current_el);
-        assert(flags == env->hflags);
         flags = FIELD_DP32(flags, TBFLAG_A64, BTYPE, env->btype);
         pstate_for_ss = env->pstate;
     } else {
         *pc = env->regs[15];
-        flags = rebuild_hflags_a32(env, current_el);
-        assert(flags == env->hflags);
         flags = FIELD_DP32(flags, TBFLAG_A32, THUMB, env->thumb);
         flags = FIELD_DP32(flags, TBFLAG_A32, CONDEXEC, env->condexec_bits);
         pstate_for_ss = env->uncached_cpsr;
-- 
2.17.1