accel/tcg: cache single instruction TB on pending replay exception

Again there is no reason to jump through the nocache hoops to execute
a single instruction block. We do have to add an additional wrinkle to
the cpu_handle_interrupt case to ensure we let through a TB where we
have specifically disabled icount for the block.

As the last user of cpu_exec_nocache we can now remove the function.
Further clean-up will follow in subsequent patches.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20210213130325.14781-18-alex.bennee@linaro.org>

accel/tcg/cpu-exec.c

@@ -224,40 +224,6 @@ cpu_tb_exec(CPUState *cpu, TranslationBlock *itb, int *tb_exit)
     return last_tb;
 }
 
-#ifndef CONFIG_USER_ONLY
-/* Execute the code without caching the generated code. An interpreter
-   could be used if available. */
-static void cpu_exec_nocache(CPUState *cpu, int max_cycles,
-                             TranslationBlock *orig_tb, bool ignore_icount)
-{
-    TranslationBlock *tb;
-    uint32_t cflags = curr_cflags() | CF_NOCACHE;
-    int tb_exit;
-
-    if (ignore_icount) {
-        cflags &= ~CF_USE_ICOUNT;
-    }
-
-    /* Should never happen.
-       We only end up here when an existing TB is too long.  */
-    cflags |= MIN(max_cycles, CF_COUNT_MASK);
-
-    mmap_lock();
-    tb = tb_gen_code(cpu, orig_tb->pc, orig_tb->cs_base,
-                     orig_tb->flags, cflags);
-    tb->orig_tb = orig_tb;
-    mmap_unlock();
-
-    /* execute the generated code */
-    trace_exec_tb_nocache(tb, tb->pc);
-    cpu_tb_exec(cpu, tb, &tb_exit);
-
-    mmap_lock();
-    tb_phys_invalidate(tb, -1);
-    mmap_unlock();
-    tcg_tb_remove(tb);
-}
-#endif
 
 static void cpu_exec_enter(CPUState *cpu)
 {
@@ -524,15 +490,12 @@ static inline bool cpu_handle_exception(CPUState *cpu, int *ret)
 #ifndef CONFIG_USER_ONLY
         if (replay_has_exception()
             && cpu_neg(cpu)->icount_decr.u16.low + cpu->icount_extra == 0) {
-            /* try to cause an exception pending in the log */
-            cpu_exec_nocache(cpu, 1, tb_find(cpu, NULL, 0, curr_cflags()), true);
+            /* Execute just one insn to trigger exception pending in the log */
+            cpu->cflags_next_tb = (curr_cflags() & ~CF_USE_ICOUNT) | 1;
         }
 #endif
-        if (cpu->exception_index < 0) {
-            return false;
-        }
+        return false;
     }
-
     if (cpu->exception_index >= EXCP_INTERRUPT) {
         /* exit request from the cpu execution loop */
         *ret = cpu->exception_index;
@@ -688,6 +651,7 @@ static inline bool cpu_handle_interrupt(CPUState *cpu,
     /* Finally, check if we need to exit to the main loop.  */
     if (unlikely(qatomic_read(&cpu->exit_request))
         || (icount_enabled()
+            && (cpu->cflags_next_tb == -1 || cpu->cflags_next_tb & CF_USE_ICOUNT)
             && cpu_neg(cpu)->icount_decr.u16.low + cpu->icount_extra == 0)) {
         qatomic_set(&cpu->exit_request, 0);
         if (cpu->exception_index == -1) {