[memprof] Add extractCallsFromIR (#115218)

This patch adds extractCallsFromIR, a function to extract calls from
the IR, which will be used to undrift call site locations in the
MemProf profile.

In a nutshell, the MemProf undrifting works as follows:

- Extract call site locations from the IR.
- Extract call site locations from the MemProf profile.
- Undrift the call site locations with longestCommonSequence.

This patch implements the first bullet point above.  Specifically,
given the IR, the new function returns a map from caller GUIDs to
lists of corresponding call sites.  For example:

Given:

  foo() {
    f1();
    f2(); f3();
  }

extractCallsFromIR returns:

  Caller: foo ->
    {{(Line 1, Column 3), Callee: f1},
     {(Line 2, Column 3), Callee: f2},
     {(Line 2, Column 9), Callee: f3}}

where the line numbers, relative to the beginning of the caller, and
column numbers are sorted in the ascending order.  The value side of
the map -- the list of call sites -- can be directly passed to
longestCommonSequence.

To facilitate the review process, I've only implemented basic features
in extractCallsFromIR in this patch.

- The new function extracts calls from the LLVM "call" instructions
  only.  It does not look into the inline stack.
- It does not recognize or treat heap allocation functions in any
  special way.

I will address these missing features in subsequent patches.

0 files changed, 0 insertions, 0 deletions