[all-commits] [llvm/llvm-project] e1871d: [libc][__support] Implement exact linear binning f...

[Schrodinger ZHU Yifan via All-commits]

  Branch: refs/heads/users/schrodingerzhu/libc-use-tlsf-freestore
  Home:   https://github.com/llvm/llvm-project
  Commit: e1871dcedc18738f23433422410dc360cef1f8d9
      https://github.com/llvm/llvm-project/commit/e1871dcedc18738f23433422410dc360cef1f8d9
  Author: Yifan Zhu <yfzhu at google.com>
  Date:   2026-07-31 (Fri, 31 Jul 2026)

  Changed paths:
    M libc/src/__support/freestore.h
    M libc/test/src/__support/freelist_heap_test.cpp
    M libc/test/src/__support/freestore_test.cpp

  Log Message:
  -----------
  [libc][__support] Implement exact linear binning for TLSFFreeStoreImpl

Previously, size_to_bit_index used size >> UNIT_SIZE_LOG2 for linear bins,
which mapped size 24 to bin 1 and size 17 to bin 1, causing a mismatch
between allocation request sizes and physical block bucket sizes.

This change introduces exact mapping for linear bins:
- Introduces LINEAR_BINS to compute the exact number of linear bins needed
  to reach the exponential table boundary (29 on MSVC Windows where UNIT_SIZE is 8,
  31 on Linux where UNIT_SIZE is 16).
- Sizes <= MIN_INNER_SIZE map to bin 0.
- Larger linear sizes map to ((size - MIN_INNER_SIZE - 1) >> UNIT_SIZE_LOG2) + 1.
- Uses LINEAR_BINS as the base index for exponential bins in size_to_bit_index,
  index_to_min_size, and find_and_remove_fit, ensuring strict monotonicity
  across all indices without runtime clamping.
- Adds NegativeTestForFullHeap unit test in freelist_heap_test.cpp and updates
  freestore_test.cpp.

TAG=agy
CONV=cff84e8c-ee22-4f39-af3c-344d1e6f417b



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