Re: Constant propagation and CSE

[Jeff Law <law at redhat dot com>]

 On 10/25/10 02:46, Frederic Riss wrote:
> Hi,
>
> The constant propagation pass propagates constants into the
> instructions that accept immediates. I'm trying to find if there's
> some CSE pass in GCC that would be able to undo this effect when the
> constant is used more than once in the function. I looked at the CSE
> code (4.5 branch) and I don't think this is currently possible. If the
> code uses a bunch of big constants, the effect on code size might be
> quite sensible.
There is currently no pass which does "un-cse"; however, using insn 
splitting and operand costing and suitable insn constraints/predicates  
you can usually arrange to avoid expensive constants in places where it 
makes sense.

Perhaps if you gave us more information about the target and the 
situations you're trying to avoid we could give more specific advice.

Jeff