Hi,
just a high level question. I know that IPA-PTA is a SIMPLE_IPA_PASS
and that ideally it would be better as an IPA_PASS. I understand that
one of the biggest challenges of changing IPA-PTA to an IPA_PASS is
that on the current LTO framework, the LTRANS stage can happen at the
same time for multiple transformations. This means (I think) that if
IPA-PTA computed the points-to sets during WPA, during LTRANS there
can be new variables, or modified function bodies that therefore no
longer correspond to the computed IPA-PTA.
However, it seems that there's a simpler way to change IPA-PTA to an
IPA_PASS. This is by just introducing another section of
"all_regular_ipa_passes". Something like (not sure if the name inside
the brackets has to be unique)
INSERT_PASSES_AFTER (all_regular_ipa_passes)
// normal stuff
TERMINATE_PASS_LIST (all_regular_ipa_passes)
INSERT_PASSES_AFTER (all_regular_ipa_passes)
NEXT_PASS (pass_ipa_pta);
TERMINATE_PASS_LIST (all_regular_ipa_passes)
I understand that this still singles out IPA-PTA as being "special",
but I am wondering if this is something that has been discussed
previously. The changes in the implementation on IPA-PTA should be
something like:
1. LGEN: in summaries store the constraint variables that GCC is
finding by inspecting gimple
2. WPA: actually solve the constraint variables and store only the
solutions to the constraint variables in another summary
3. LTRANS: read from the summary and pass the information to gimple
The advantage I see to this is that the precision of IPA-PTA would be
equal to using -flto-partition=none but without actually using that
flag and possibly some compile time speedup (when compared to
-flto-partition=none because parallel reading and writing of
summaries). Again, just an idea and I just want to understand if this
has been discussed before and why it is or might not be something that
you guys want.
