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accel/tcg: Remove unnecessary check on icount_extra in cpu_loop_exec_tb()

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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>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20210725174405.24568-3-peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
This commit is contained in:
Peter Maydell 2021-07-25 18:44:05 +01:00 committed by Richard Henderson
parent df3a2de51a
commit c8cf47a946
1 changed files with 3 additions and 1 deletions
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4
accel/tcg/cpu-exec.c
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@ -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