[LLVMdev] [LLVM Dev] [Discussion] Function-based parallel LLVM backend code generation
chandlerc at google.com
Tue Jul 16 13:40:26 PDT 2013
On Tue, Jul 16, 2013 at 1:37 PM, Xinliang David Li <xinliangli at gmail.com>wrote:
> On Tue, Jul 16, 2013 at 1:33 PM, Chandler Carruth <chandlerc at google.com>
> > On Tue, Jul 16, 2013 at 1:18 PM, Xinliang David Li <xinliangli at gmail.com
> > wrote:
> >> Ignoring FE time which can be fully parallelized and assuming 10%
> >> compile time is spent in serial module passes, 25% time is spent in
> >> CGSCC pass, the maximum speed up that can be gained by using function
> >> level parallelism is less than 3x. Even adding support for parallel
> >> compilation for leaves of CG in CGSCC pass won't help too much -- the
> >> percentage of leaf functions is < 30% in large apps I have seen.
> > Can you clarify what you're basing these assumption on or how you derived
> > your data?
> Those numbers are purely speculative -- does Clang has an option to
> dump the time breakout of each passes such as -ftime-report in GCC?
We have the functionality... I thought we wired -ftime-report up to it? If
that doesn't work I'll have to go digging.
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