Hazard Detection

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Hi

I have a question: I compiled a program with  gcc
-mips1 ,
Compiler generate this list of instructions:
  
...               ....    
          ...
  10b71c:  
 87a20018      lh      
 v0,24(sp)
  10b720:    00000000    
nop
  10b724:    144000b9     bnez  
 v0,10ba0c
  10b728:    0015ac03    
 sra      s5,s5,0x10
   ...    
          ....          
    ...

but by a small change, some times in
variables, (using same compiler
switches) compiler don't insert
 nop between load and branch and generates
this sequence of
instructions:
   ...            
  ....               ...

 10b754:    87a20018     lh      
  v0,24(sp)
  10b758:    144000b9    
bnez     v0,10ba40
  10b75c:    0015ac03
     sra       s5,s5,0x10
   ...
              ....      
        ...

would you please tell me the
reason?

why doesn't compiler detect hazard always?

Thanks in advanced.

Neda Zolfaghari (zneda@xxxxxxxxx)


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