[PATCH] Indirect call target profiling compiler-rt changes

[Betul Buyukkurt]

> I think there is more room to reduce memory footprint and profile data
size.
> The reason that value_kind and counter index needs to be recorded and
stored is because the number of value entries per site is variant. This
problem can be solved by adding one level of indirection when writing
out
> the profile data: Writing out ValueCounters in profile data too (with
address fixup after data gathering). With that written out, the
> llvm_profile_value data can be greatly shrinked:

Hi David,

Here is what you're suggesting per my understanding.

In the raw profile output file, ValueCounters array of __llvm_profile_data
should point to another array of size NumValueSites. This array is created
dynamically at runtime, but will also be written out to the profile data
file. Each element of this new array in the output file will point to the
beginning of the relevant __llvm_profile_value_data* entries for a
value_kind and a counter_index.

__llvm_profile_gather_value_data routine will be responsible for forming
both the __llvm_profile_value_data* array (i.e. ValueProfilingResults) as
well as the new pointer array for the added indirection.

One extra piece of information that needs to be stored is the number of
elements that each pointer in the indirection array points to. In the
least we have to store the number of elements that the last element in the
indirection array points to. This way we may eliminate the need to store
the counter index, function index and the value_kinds in each value data
field.

Please confirm if anything is missing from the above. Since the raw
profile format does not have to be maintained and remain backwards
compatible (per Justin's comments), this optimization can be added after
all the patches merge in. So this should not really hold the patches from
merging in. Do you agree?

-Betul

> 1. in memory: it needs only 3 64bit integers instead of 4
> 2. in disk: it needs only 2 64bit integers instead of the current 4 (No
need for func index either).
> http://reviews.llvm.org/D9009
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