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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