Change string compression encoding.

Encode the string compression flag as the least significant
bit of the "count" field, with 0 meaning compressed and 1
meaning uncompressed.

The main vdex file is a tiny bit larger (+28B for prebuilt
boot images, +32 for on-device built images) and the oat
file sizes change. Measured on Nexus 9, AOSP ToT, these
changes are insignificant when string compression is
disabled (-200B for the 32-bit boot*.oat for prebuilt boot
image, -4KiB when built on the device attributable to
rounding, -16B for 64-bit boot*.oat for prebuilt boot image,
no change when built on device) but with string compression
enabled we get significant differences:
  prebuilt multi-part boot image:
    - 32-bit boot*.oat: -28KiB
    - 64-bit boot*.oat: -24KiB
  on-device built single boot image:
    - 32-bit boot.oat: -32KiB
    - 64-bit boot.oat: -28KiB
The boot image oat file overhead for string compression:
  prebuilt multi-part boot image:
    - 32-bit boot*.oat: before: ~80KiB after: ~52KiB
    - 64-bit boot*.oat: before: ~116KiB after: ~92KiB
  on-device built single boot image:
    - 32-bit boot.oat: before: 92KiB after: 60KiB
    - 64-bit boot.oat: before: 116KiB after: 92KiB

The differences in the SplitStringBenchmark seem to be lost
in the noise.

Test: Run ART test suite on host and Nexus 9 with Optimizing.
Test: Run ART test suite on host and Nexus 9 with interpreter.
Test: All of the above with string compression enabled.
Bug: 31040547

Change-Id: I7570c2b700f1a31004a2d3c18b1cc30046d35a74

0 files changed, 0 insertions, 0 deletions