[Patch]Do not simplifyLatch for loops where hoisting increments could result in extra live range interferance

[yi_jiang]

Hi, 

This path is to address a typical code as find loop with early exit. 
        for ( ; i!=end  ; i++) {
           if (i == k)
             break; 

           ...
        }
      
        if (i == end) 
          ...
And the IR is:
 for.cond:                                         ; preds = %for.inc, %entry
   ...

for.body:                                         ; preds = %for.cond
  %0 = load i32* %coerce.val.ip9, align 4, !tbaa !1
  ...
  br i1 %cmp, label %for.end, label %for.inc    // early exit

for.inc:                                          ; preds = %for.body
  %incdec.ptr.i = getelementptr inbounds i32* %coerce.val.ip9, i64 1
  br label %for.cond

If we hoist the increment in the for.inc to the for.body then it will cause extra live range interference and hurt the performance. So this patch will check for uses of the increments operand and do not hoist if there are outside users. 

This patch will improve the spec2006 case xalanbmk(ref size) by 10% on arm64. We do not see regressions on arm64 and on x86 we see 1% regression on the case: SingleSource/Benchmarks/BenchmarkGame/fannkuch. The reasons is that if the increments in the latch was hoist, it can be combined with some other instruction which make it beneficial in this case even with live range interference.  Thank you for reviewing it. 

-Yi
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