Hoàng Minh Thiên
582643f1ec
This PR adds a new option ~~`LIBC_MATH_ALWAYS_ROUND_NEAREST`~~ `LIBC_MATH_ASSUME_ROUND_NEAREST_ONLY` to LLVM libm. There are some UBs that I kept as-is from the original code to keep the changes non-disruptive (which I've marked with TODO comments) Benchmarks (from `files.zip` in the comment https://github.com/llvm/llvm-project/issues/198276#issue-4468816457): - System libm: ``` overflow (>710) 1.55 ns/call (644M ops/sec) underflow to 0 (<-746) 1.34 ns/call (747M ops/sec) normal [-10,10] 4.41 ns/call (227M ops/sec) denormals [-740,-735] 2.25 ns/call (444M ops/sec) near-uflow [-700,-690] 2.25 ns/call (444M ops/sec) ``` - LLVM libm (without the option being set): ``` overflow (>710) 5.21 ns/call (192M ops/sec) underflow to 0 (<-746) 7.20 ns/call (139M ops/sec) normal [-10,10] 4.06 ns/call (246M ops/sec) denormals [-740,-735] 5.85 ns/call (171M ops/sec) near-uflow [-700,-690] 4.06 ns/call (246M ops/sec) ``` - LLVM libm (with the option being **set**, `bench-exp-paths-inc.cc`) ``` overflow (>710) 1.95 ns/call (514M ops/sec) underflow to 0 (<-746) 2.23 ns/call (449M ops/sec) normal [-10,10] 3.43 ns/call (292M ops/sec) denormals [-740,-735] 5.19 ns/call (193M ops/sec) near-uflow [-700,-690] 3.43 ns/call (292M ops/sec) ``` Notice that in the `bench-exp-paths-inc.cc` file, I've changed the option name from `LIBC_MATH_ROUND_NEAREST` to `LIBC_MATH_ASSUME_ROUND_NEAREST_ONLY` Benchmark system: macOS 26.5, Apple M3.
63 lines
1.7 KiB
C++
63 lines
1.7 KiB
C++
//===-- RoundingModeUtils.cpp ---------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#undef LIBC_MATH_USE_SYSTEM_FENV
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#include "RoundingModeUtils.h"
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#include "src/__support/FPUtil/FEnvImpl.h"
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#include "src/__support/FPUtil/rounding_mode.h"
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#include "hdr/fenv_macros.h"
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#include "src/__support/macros/config.h"
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namespace LIBC_NAMESPACE_DECL {
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namespace fputil {
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namespace testing {
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int get_fe_rounding(RoundingMode mode) {
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switch (mode) {
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case RoundingMode::Upward:
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return FE_UPWARD;
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case RoundingMode::Downward:
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return FE_DOWNWARD;
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case RoundingMode::TowardZero:
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return FE_TOWARDZERO;
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case RoundingMode::Nearest:
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return FE_TONEAREST;
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}
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__builtin_unreachable();
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}
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ForceRoundingMode::ForceRoundingMode(RoundingMode mode) {
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#ifdef LIBC_MATH_HAS_ASSUME_ROUND_NEAREST_ONLY
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old_rounding_mode = FE_TONEAREST;
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rounding_mode = FE_TONEAREST;
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success = (mode == RoundingMode::Nearest);
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#else
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old_rounding_mode = quick_get_round();
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rounding_mode = get_fe_rounding(mode);
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if (old_rounding_mode != rounding_mode) {
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int status = set_round(rounding_mode);
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success = (status == 0);
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} else {
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success = true;
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}
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#endif // LIBC_MATH_HAS_ASSUME_ROUND_NEAREST_ONLY
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}
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ForceRoundingMode::~ForceRoundingMode() {
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#ifndef LIBC_MATH_HAS_ASSUME_ROUND_NEAREST_ONLY
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if (old_rounding_mode != rounding_mode)
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set_round(old_rounding_mode);
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#endif
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}
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} // namespace testing
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} // namespace fputil
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} // namespace LIBC_NAMESPACE_DECL
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