Re: asking the flow analysis not to optimize

[tm <tm at kloo dot net>]

thomas joseph wrote:
> 
> Hi All
>   I am facing a small problem with my new gcc port.
>  For generating code for compare and branches, I am
> saving the operands in cmp patterns and generating
> code in branch (beq, bgt etc.,) patterns.
> 
>    The word size is 16 bit and I do n't have 16 bit
>   compare instruction on my machine. So
>  for longs (32 bits), I generate code like this ....
> 
>    1).   < clear the flags>
>    2).    sbc lo0, lo1
>    3).    sbc  hio, hi1
> 
>   So , now I jump based on the flags. But actually
>  when I compile a sample code with optimization's on
>  the first instruction is being pulled out during flow
> analysis. So, I get the wrong code. So, how do I tell
> the flow analysis  not to delete that particular
> instruction or rtl insn (basically generated by
> emit_insn () .)
> 
>     Any suggestions would be of great help.....
> 
> thanks and regards,
> 
> thomas

You need to trace through flow and figure out why
your insn is being deleted.

My guess is that flow thinks it's a dead insn, e.g.
it generates a result which is never used.

Toshi