From: ThatWouldBeTelling@thevillage.com   
      
   Terje Mathisen wrote:   
   > EricP wrote:   
   >>   
   >> The only instruction usage stats I have are from those VAX papers:   
   >> A Case Study of VAX-11 Instruction Set Usage For Compiler Execution, 1982   
   >>   
   >> That shows about 12% instructions are conditional branch and 9% CMP.   
   >> That says to me that almost all Bcc are paired with a CMP,   
   >> and very few use the flags set as a side effect of ALU ops.   
   >>   
   >> I would expect those two numbers to be closer as even today compilers   
   >> don't   
   >> know about those side effect flags and will always emit a CMP or TST   
   >> first.   
   >   
   > I know I have seen lots of examples of x86 compilers which used side   
   > effect flags, they are pretty much the standard idiom for decrementing   
   > loops or incrementing from negative start. The latter case is a common   
   > optimization which allows you to use the same register as the source   
   > index/indices and the destination index, along with the loop counter   
   > itself.   
   >   
   > Terje   
      
   My mistake. I haven't seen the MS C compiler do this and erroneously   
   assumed without checking that no one does it, perhaps due to portability   
   issues particularly for x86 with its asymmetric flags updates.   
      
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