[PATCH for-6.1 2/2] accel/tcg: Remove unnecessary check on icount_extra in cpu_loop_exec_tb()

[Peter Maydell]

In cpu_loop_exec_tb(), we decide whether to look for a TB with
exactly insns_left instructions in it using the condition
 (!cpu->icount_extra && insns_left > 0 && insns_left < tb->icount)

The check for icount_extra == 0 is unnecessary, because we just set
  insns_left = MIN(0xffff, cpu->icount_budget);
  icount_extra = icount_budget - insns_left;
and so icount_extra can only be non-zero if icount_budget > 0xffff
and insns_left == 0xffff. But in that case insns_left >= tb->icount
because 0xffff is much larger than TCG_MAX_INSNS, so the condition
will be false anyway.

Remove the unnecessary check, and instead assert:
 * that we are only going to execute a partial TB here if the
   icount budget has run out (ie icount_extra == 0)
 * that the number of insns we're going to execute does fit into
   the CF_COUNT_MASK

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
You could argue that we don't need the asserts, if you like.
The first one would have caught the bug fixed in the previous
commit, though.
---
 accel/tcg/cpu-exec.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/accel/tcg/cpu-exec.c b/accel/tcg/cpu-exec.c
index 6e8dc291197..5aa42fbff35 100644
--- a/accel/tcg/cpu-exec.c
+++ b/accel/tcg/cpu-exec.c
@@ -843,7 +843,9 @@ static inline void cpu_loop_exec_tb(CPUState *cpu, 
TranslationBlock *tb,
      * execute we need to ensure we find/generate a TB with exactly
      * insns_left instructions in it.
      */
-    if (!cpu->icount_extra && insns_left > 0 && insns_left < tb->icount)  {
+    if (insns_left > 0 && insns_left < tb->icount)  {
+        assert(insns_left <= CF_COUNT_MASK);
+        assert(cpu->icount_extra == 0);
         cpu->cflags_next_tb = (tb->cflags & ~CF_COUNT_MASK) | insns_left;
     }
 #endif
-- 
2.20.1