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Denormal numbers (see [1]) may origin in APM when the input is zeroed after a non-zero signal. In extreme cases, instructions involving denormal operands may run as much as 100 times slower, which seems to be the case (to some extent) of crbug.com/1227566. This CL adds a class that disables denormals only via hardware on x86 and on ARM. The class is used in APM and it is an adaption of [2]. Tested: appr.tc call on Chromium (Win, Mac) [1] https://en.wikipedia.org/wiki/Denormal_number [2] https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/renderer/platform/audio/denormal_disabler.h Fixed: chromium:1227566 Change-Id: I0ed2eab55dc597529f09f93c26c7a01de051fdbe Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/227768 Reviewed-by: Magnus Flodman <mflodman@webrtc.org> Reviewed-by: Per Åhgren <peah@webrtc.org> Commit-Queue: Alessio Bazzica <alessiob@webrtc.org> Cr-Commit-Position: refs/heads/master@{#34701}
54 lines
1.9 KiB
C++
54 lines
1.9 KiB
C++
/*
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* Copyright (c) 2021 The WebRTC project authors. All Rights Reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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#ifndef SYSTEM_WRAPPERS_INCLUDE_DENORMAL_DISABLER_H_
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#define SYSTEM_WRAPPERS_INCLUDE_DENORMAL_DISABLER_H_
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#include "rtc_base/system/arch.h"
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namespace webrtc {
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// Activates the hardware (HW) way to flush denormals (see [1]) to zero as they
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// can very seriously impact performance. At destruction time restores the
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// denormals handling state read by the ctor; hence, supports nested calls.
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// Equals a no-op if the architecture is not x86 or ARM or if the compiler is
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// not CLANG.
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// [1] https://en.wikipedia.org/wiki/Denormal_number
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//
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// Example usage:
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//
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// void Foo() {
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// DenormalDisabler d;
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// ...
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// }
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class DenormalDisabler {
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public:
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// Ctor. If `enabled` is true and architecture and compiler are supported,
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// stores the HW settings for denormals, disables denormals and sets
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// `disabling_activated_` to true. Otherwise, only sets `disabling_activated_`
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// to false.
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explicit DenormalDisabler(bool enabled);
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DenormalDisabler(const DenormalDisabler&) = delete;
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DenormalDisabler& operator=(const DenormalDisabler&) = delete;
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// Dtor. If `disabling_activated_` is true, restores the denormals HW settings
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// read by the ctor before denormals were disabled. Otherwise it's a no-op.
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~DenormalDisabler();
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// Returns true if architecture and compiler are supported.
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static bool IsSupported();
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private:
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const int status_word_;
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const bool disabling_activated_;
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};
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} // namespace webrtc
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#endif // SYSTEM_WRAPPERS_INCLUDE_DENORMAL_DISABLER_H_
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