[PATCH] [sanitizer] Add a fast version of StackDepotGet() for use in LSan. Add a class that holds a snapshot of the StackDepot optimized for querying by ID. This allows us to speed up LSan dramatically.

[Kostya Serebryany]

  I am ok with this change as a temporary measure, but long term we need to fix ld.so problem in lsan in some more efficient way, e.g.
  by checking that the caller address in memalign belongs to ld.so.
  Sergey,  please make sure to explain the situation in detail in a bug report.

http://llvm-reviews.chandlerc.com/D1496

BRANCH
  fix/stackdepot

ARCANIST PROJECT
  compiler-rt