[hwasan] Madvise away unused shadow.

Summary:
Whenever a large shadow region is tagged to zero, madvise(DONT_NEED)
as much of it as possible.

This reduces shadow RSS on Android by 45% or so, and total memory use
by 2-4%, probably even more on long running multithreaded programs.
CPU time seems to be in the noise.

Reviewers: kcc, pcc

Subscribers: srhines, kubamracek, llvm-commits

Differential Revision: https://reviews.llvm.org/D56757

llvm-svn: 351620
4 files changed
tree: 9ae65fbeb4ac59a09f3e068a46874923eecdd045
  1. clang/
  2. clang-tools-extra/
  3. compiler-rt/
  4. debuginfo-tests/
  5. libclc/
  6. libcxx/
  7. libcxxabi/
  8. libunwind/
  9. lld/
  10. lldb/
  11. llgo/
  12. llvm/
  13. openmp/
  14. parallel-libs/
  15. polly/
  16. pstl/
  17. .arcconfig
  18. README.md
README.md

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This directory and its subdirectories contain source code for LLVM, a toolkit for the construction of highly optimized compilers, optimizers, and runtime environments.