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
diff --git a/compiler/optimizing/code_generator_arm_vixl.cc b/compiler/optimizing/code_generator_arm_vixl.cc
index e69528e..254d908 100644
--- a/compiler/optimizing/code_generator_arm_vixl.cc
+++ b/compiler/optimizing/code_generator_arm_vixl.cc
@@ -3790,16 +3790,21 @@
case Primitive::kPrimShort:
case Primitive::kPrimChar:
case Primitive::kPrimInt: {
+ vixl32::Register length;
+ if (maybe_compressed_char_at) {
+ length = RegisterFrom(locations->GetTemp(0));
+ uint32_t count_offset = mirror::String::CountOffset().Uint32Value();
+ GetAssembler()->LoadFromOffset(kLoadWord, length, obj, count_offset);
+ codegen_->MaybeRecordImplicitNullCheck(instruction);
+ }
if (index.IsConstant()) {
int32_t const_index = index.GetConstant()->AsIntConstant()->GetValue();
if (maybe_compressed_char_at) {
- vixl32::Register length = temps.Acquire();
vixl32::Label uncompressed_load, done;
- uint32_t count_offset = mirror::String::CountOffset().Uint32Value();
- GetAssembler()->LoadFromOffset(kLoadWord, length, obj, count_offset);
- codegen_->MaybeRecordImplicitNullCheck(instruction);
- __ Cmp(length, 0);
- __ B(ge, &uncompressed_load);
+ __ Lsrs(length, length, 1u); // LSRS has a 16-bit encoding, TST (immediate) does not.
+ static_assert(static_cast<uint32_t>(mirror::StringCompressionFlag::kCompressed) == 0u,
+ "Expecting 0=compressed, 1=uncompressed");
+ __ B(cs, &uncompressed_load);
GetAssembler()->LoadFromOffset(kLoadUnsignedByte,
RegisterFrom(out_loc),
obj,
@@ -3827,12 +3832,10 @@
}
if (maybe_compressed_char_at) {
vixl32::Label uncompressed_load, done;
- uint32_t count_offset = mirror::String::CountOffset().Uint32Value();
- vixl32::Register length = RegisterFrom(locations->GetTemp(0));
- GetAssembler()->LoadFromOffset(kLoadWord, length, obj, count_offset);
- codegen_->MaybeRecordImplicitNullCheck(instruction);
- __ Cmp(length, 0);
- __ B(ge, &uncompressed_load);
+ __ Lsrs(length, length, 1u); // LSRS has a 16-bit encoding, TST (immediate) does not.
+ static_assert(static_cast<uint32_t>(mirror::StringCompressionFlag::kCompressed) == 0u,
+ "Expecting 0=compressed, 1=uncompressed");
+ __ B(cs, &uncompressed_load);
__ Ldrb(RegisterFrom(out_loc), MemOperand(temp, RegisterFrom(index), vixl32::LSL, 0));
__ B(&done);
__ Bind(&uncompressed_load);
@@ -4211,7 +4214,7 @@
codegen_->MaybeRecordImplicitNullCheck(instruction);
// Mask out compression flag from String's array length.
if (mirror::kUseStringCompression && instruction->IsStringLength()) {
- __ Bic(out, out, 1u << 31);
+ __ Lsr(out, out, 1u);
}
}