exec: drop cpu_can_do_io, just read cpu->can_do_io

After commit 626cf8f (icount: set can_do_io outside TB execution,
2014-12-08), can_do_io is set to 1 if not executing code.  It is
no longer necessary to make this assumption in cpu_can_do_io.

It is also possible to remove the use_icount test, simply by
never setting cpu->can_do_io to 0 unless use_icount is true.

With these changes cpu_can_do_io boils down to a read of
cpu->can_do_io.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/include/qom/cpu.h b/include/qom/cpu.h
index 20aabc9..39712ab 100644
--- a/include/qom/cpu.h
+++ b/include/qom/cpu.h
@@ -231,7 +231,9 @@ struct kvm_run;
  * @icount_decr: Number of cycles left, with interrupt flag in high bit.
  * This allows a single read-compare-cbranch-write sequence to test
  * for both decrementer underflow and exceptions.
- * @can_do_io: Nonzero if memory-mapped IO is safe.
+ * @can_do_io: Nonzero if memory-mapped IO is safe. Deterministic execution
+ * requires that IO only be performed on the last instruction of a TB
+ * so that interrupts take effect immediately.
  * @env_ptr: Pointer to subclass-specific CPUArchState field.
  * @current_tb: Currently executing TB.
  * @gdb_regs: Additional GDB registers.