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Export of internal Abseil changes

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d447fdcb801036cf08197eece193a5a706661120 by Gennadiy Rozental <rogeeff@google.com>:

Eliminate the need for static function holding help message. This decreases the cost of ABSL_FLAG abstraction by 120 bytes under clang.

PiperOrigin-RevId: 281107806

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0aa6b91189f0e8b2381438c33465673a7ae02487 by Derek Mauro <dmauro@google.com>:

Disable the weak symbol CCTZ extension in the time test_util
on MinGW, which does not support it.

PiperOrigin-RevId: 280719769

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67322c41c3e776eb541de90fa4526bdb49422eb6 by Abseil Team <absl-team@google.com>:

Tune PeriodicSampler implementation (for internal-use only)

PiperOrigin-RevId: 280708943

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3a48c346340c7ed03816645cd327e1ff07729aa4 by Abseil Team <absl-team@google.com>:

Clean up public headers not to have warnings for "-Wcomma"

PiperOrigin-RevId: 280695373

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981acd1ef3b13a83a84f04f11c8931f4ed4451c9 by Matthew Brown <matthewbr@google.com>:

Release absl::int128.

PiperOrigin-RevId: 280690817

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d30fae9d2ec30b81322d2eb5afe7e13e45b4b422 by Derek Mauro <dmauro@google.com>:

Fix -Wundef warnings in random platform detection

PiperOrigin-RevId: 280669598
GitOrigin-RevId: d447fdcb801036cf08197eece193a5a706661120
Change-Id: Ie5e10e567c54b7de211833607689f233d4ddf734
This commit is contained in:
Abseil Team 2019-11-18 11:02:26 -08:00 • committed by Gennadiy Civil
parent 3df7b52a6a
commit 2103fd9acd
23 changed files with 2800 additions and 136 deletions
Download patch file Download diff file Expand all files Collapse all files

35
absl/base/internal/bits.h
View file

@ -50,10 +50,22 @@ namespace base_internal {
ABSL_BASE_INTERNAL_FORCEINLINE int CountLeadingZeros64Slow(uint64_t n) {
int zeroes = 60;
if (n >> 32) zeroes -= 32, n >>= 32;
if (n >> 16) zeroes -= 16, n >>= 16;
if (n >> 8) zeroes -= 8, n >>= 8;
if (n >> 4) zeroes -= 4, n >>= 4;
if (n >> 32) {
zeroes -= 32;
n >>= 32;
}
if (n >> 16) {
zeroes -= 16;
n >>= 16;
}
if (n >> 8) {
zeroes -= 8;
n >>= 8;
}
if (n >> 4) {
zeroes -= 4;
n >>= 4;
}
return "\4\3\2\2\1\1\1\1\0\0\0\0\0\0\0"[n] + zeroes;
}
@ -95,9 +107,18 @@ ABSL_BASE_INTERNAL_FORCEINLINE int CountLeadingZeros64(uint64_t n) {
ABSL_BASE_INTERNAL_FORCEINLINE int CountLeadingZeros32Slow(uint64_t n) {
int zeroes = 28;
if (n >> 16) zeroes -= 16, n >>= 16;
if (n >> 8) zeroes -= 8, n >>= 8;
if (n >> 4) zeroes -= 4, n >>= 4;
if (n >> 16) {
zeroes -= 16;
n >>= 16;
}
if (n >> 8) {
zeroes -= 8;
n >>= 8;
}
if (n >> 4) {
zeroes -= 4;
n >>= 4;
}
return "\4\3\2\2\1\1\1\1\0\0\0\0\0\0\0"[n] + zeroes;
}

6
absl/base/internal/periodic_sampler.cc
View file

@ -36,13 +36,13 @@ bool PeriodicSamplerBase::SubtleConfirmSample() noexcept {
// Check if this is the first call to Sample()
if (ABSL_PREDICT_FALSE(stride_ == 1)) {
stride_ = -1 - GetExponentialBiased(current_period);
if (stride_ < -1) {
stride_ = static_cast<uint64_t>(-1 - GetExponentialBiased(current_period));
if (static_cast<int64_t>(stride_) < -1) {
++stride_;
return false;
}
}
stride_ = -1 - GetExponentialBiased(current_period);
stride_ = static_cast<uint64_t>(-1 - GetExponentialBiased(current_period));
return true;
}

62
absl/base/internal/periodic_sampler.h
View file

@ -111,33 +111,49 @@ class PeriodicSamplerBase {
// Returns the current period of this sampler. Thread-safe.
virtual int period() const noexcept = 0;
int64_t stride_ = 0;
// Keep and decrement stride_ as an unsigned integer, but compare the value
// to zero casted as a signed int. clang and msvc do not create optimum code
// if we use signed for the combined decrement and sign comparison.
//
// Below 3 alternative options, all compiles generate the best code
// using the unsigned increment <---> signed int comparison option.
//
// Option 1:
// int64_t stride_;
// if (ABSL_PREDICT_TRUE(++stride_ < 0)) { ... }
//
// GCC x64 (OK) : https://gcc.godbolt.org/z/R5MzzA
// GCC ppc (OK) : https://gcc.godbolt.org/z/z7NZAt
// Clang x64 (BAD): https://gcc.godbolt.org/z/t4gPsd
// ICC x64 (OK) : https://gcc.godbolt.org/z/rE6s8W
// MSVC x64 (OK) : https://gcc.godbolt.org/z/ARMXqS
//
// Option 2:
// int64_t stride_ = 0;
// if (ABSL_PREDICT_TRUE(--stride_ >= 0)) { ... }
//
// GCC x64 (OK) : https://gcc.godbolt.org/z/jSQxYK
// GCC ppc (OK) : https://gcc.godbolt.org/z/VJdYaA
// Clang x64 (BAD): https://gcc.godbolt.org/z/Xm4NjX
// ICC x64 (OK) : https://gcc.godbolt.org/z/4snaFd
// MSVC x64 (BAD): https://gcc.godbolt.org/z/BgnEKE
//
// Option 3:
// uint64_t stride_;
// if (ABSL_PREDICT_TRUE(static_cast<int64_t>(++stride_) < 0)) { ... }
//
// GCC x64 (OK) : https://gcc.godbolt.org/z/bFbfPy
// GCC ppc (OK) : https://gcc.godbolt.org/z/S9KkUE
// Clang x64 (OK) : https://gcc.godbolt.org/z/UYzRb4
// ICC x64 (OK) : https://gcc.godbolt.org/z/ptTNfD
// MSVC x64 (OK) : https://gcc.godbolt.org/z/76j4-5
uint64_t stride_ = 0;
ExponentialBiased rng_;
};
inline bool PeriodicSamplerBase::SubtleMaybeSample() noexcept {
// We explicitly count up and not down, as the compiler does not generate
// ideal code for counting down. See also https://gcc.godbolt.org/z/FTPDSM
//
// With `if (ABSL_PREDICT_FALSE(++stride_ < 0))`
// add QWORD PTR fs:sampler@tpoff+8, 1
// jns .L15
// ret
//
// With `if (ABSL_PREDICT_FALSE(--stride_ > 0))`
// mov rax, QWORD PTR fs:sampler@tpoff+8
// sub rax, 1
// mov QWORD PTR fs:sampler@tpoff+8, rax
// test rax, rax
// jle .L15
// ret
// add QWORD PTR fs:sampler@tpoff+8, 1
// jns .L15
// ret
//
// --stride >= 0 does work, but makes our logic slightly harder as in that
// case we have less convenient zero-init and over-run values.
if (ABSL_PREDICT_FALSE(++stride_ < 0)) {
// See comments on `stride_` for the unsigned increment / signed compare.
if (ABSL_PREDICT_TRUE(static_cast<int64_t>(++stride_) < 0)) {
return false;
}
return true;