[LLVMdev] flag_unit_at_a_time and pass scheduling in llvm-gcc

[Devang Patel]

On Apr 16, 2008, at 1:02 PM, Duncan Sands wrote:

> Hi Devang,
>
>> You can do inlining even when flag_unit_at_a_time is off. And one can
>> enable unit-at-a-time without enabling any optimizations.  The unit- 
>> at-
>> a-time is not meant to select optimization passes, though it may
>> influence selection.
>
> this flag is used quite a bit in llvm-backend.cpp, for example:
>
>    if (flag_unit_at_a_time) {
>      PM->add(createGlobalOptimizerPass());       // Optimize out  
> global vars
>      PM->add(createGlobalDCEPass());             // Remove unused  
> fns and globs
>      PM->add(createIPConstantPropagationPass()); // IP Constant  
> Propagation
>      PM->add(createDeadArgEliminationPass());    // Dead argument  
> elimination
>    }
>
> I thought I understood why but it seems that I don't :)

IMO, we should avoid using flag_unit_at_a_time here.

-
Devang