use [[gnu::...]] attributes

src/output/plugins/AlsaOutputPlugin.cxx

@@ -246,7 +246,7 @@ public:
 
 	using MultiSocketMonitor::GetEventLoop;
 
-	gcc_pure
+	[[gnu::pure]]
 	const char *GetDevice() const noexcept {
 		return device.empty() ? default_device : device.c_str();
 	}
@@ -292,13 +292,13 @@ private:
 #endif
 			);
 
-	gcc_pure
+	[[gnu::pure]]
 	bool LockIsActive() const noexcept {
 		const std::scoped_lock<Mutex> lock(mutex);
 		return active;
 	}
 
-	gcc_pure
+	[[gnu::pure]]
 	bool LockIsActiveAndNotWaiting() const noexcept {
 		const std::scoped_lock<Mutex> lock(mutex);
 		return active && !waiting;
@@ -654,7 +654,7 @@ MaybeDmix(snd_pcm_type_t type)
 	return type == SND_PCM_TYPE_DMIX || type == SND_PCM_TYPE_PLUG;
 }
 
-gcc_pure
+[[gnu::pure]]
 static bool
 MaybeDmix(snd_pcm_t *pcm) noexcept
 {

src/output/plugins/JackOutputPlugin.cxx

@@ -124,7 +124,7 @@ private:
 	 * Determine the number of frames guaranteed to be available
 	 * on all channels.
 	 */
-	gcc_pure
+	[[gnu::pure]]
 	jack_nframes_t GetAvailable() const noexcept;
 
 	void Process(jack_nframes_t nframes);

src/output/plugins/OSXOutputPlugin.cxx

@@ -525,7 +525,7 @@ osx_output_hog_device(AudioDeviceID dev_id, bool hog) noexcept
 	}
 }
 
-gcc_pure
+[[gnu::pure]]
 static bool
 IsAudioDeviceName(AudioDeviceID id, const char *expected_name) noexcept
 {

src/output/plugins/OpenALOutputPlugin.cxx

@@ -43,7 +43,7 @@ private:
 	void Open(AudioFormat &audio_format) override;
 	void Close() noexcept override;
 
-	[[nodiscard]] gcc_pure
+	[[nodiscard]] [[gnu::pure]]
 	std::chrono::steady_clock::duration Delay() const noexcept override {
 		return filled < NUM_BUFFERS || HasProcessed()
 			? std::chrono::steady_clock::duration::zero()
@@ -57,19 +57,19 @@ private:
 
 	void Cancel() noexcept override;
 
-	[[nodiscard]] gcc_pure
+	[[nodiscard]] [[gnu::pure]]
 	ALint GetSourceI(ALenum param) const noexcept {
 		ALint value;
 		alGetSourcei(source, param, &value);
 		return value;
 	}
 
-	[[nodiscard]] gcc_pure
+	[[nodiscard]] [[gnu::pure]]
 	bool HasProcessed() const noexcept {
 		return GetSourceI(AL_BUFFERS_PROCESSED) > 0;
 	}
 
-	[[nodiscard]] gcc_pure
+	[[nodiscard]] [[gnu::pure]]
 	bool IsPlaying() const noexcept {
 		return GetSourceI(AL_SOURCE_STATE) == AL_PLAYING;
 	}

src/output/plugins/OssOutputPlugin.cxx

@@ -372,8 +372,7 @@ oss_setup_sample_rate(FileDescriptor fd, AudioFormat &audio_format,
  * Convert a MPD sample format to its OSS counterpart.  Returns
  * AFMT_QUERY if there is no direct counterpart.
  */
-gcc_const
-static int
+static constexpr int
 sample_format_to_oss(SampleFormat format) noexcept
 {
 	switch (format) {
@@ -411,8 +410,7 @@ sample_format_to_oss(SampleFormat format) noexcept
  * Convert an OSS sample format to its MPD counterpart.  Returns
  * SampleFormat::UNDEFINED if there is no direct counterpart.
  */
-gcc_const
-static SampleFormat
+static constexpr SampleFormat
 sample_format_from_oss(int format) noexcept
 {
 	switch (format) {

src/output/plugins/RecorderOutputPlugin.cxx

@@ -72,7 +72,7 @@ private:
 
 	std::size_t Play(std::span<const std::byte> src) override;
 
-	[[nodiscard]] gcc_pure
+	[[nodiscard]] [[gnu::pure]]
 	bool HasDynamicPath() const noexcept {
 		return !format_path.empty();
 	}

src/output/plugins/WinmmOutputPlugin.hxx

@@ -8,8 +8,6 @@
 
 #ifdef ENABLE_WINMM_OUTPUT
 
-#include "util/Compiler.h"
-
 #include <windef.h>
 #include <mmsystem.h>
 
@@ -17,7 +15,7 @@ class WinmmOutput;
 
 extern const struct AudioOutputPlugin winmm_output_plugin;
 
-gcc_pure
+[[gnu::pure]]
 HWAVEOUT
 winmm_output_get_handle(WinmmOutput &output);
 

src/output/plugins/httpd/HttpdClient.cxx

@@ -153,7 +153,7 @@ HttpdClient::SendResponse() noexcept
 	}
 
 	ssize_t nbytes = GetSocket().Write(response, strlen(response));
-	if (gcc_unlikely(nbytes < 0)) {
+	if (nbytes < 0) [[unlikely]] {
 		const SocketErrorMessage msg;
 		FmtWarning(httpd_output_domain,
 			   "failed to write to client: {}",

src/output/plugins/httpd/HttpdClient.hxx

@@ -6,7 +6,6 @@
 
 #include "Page.hxx"
 #include "event/BufferedSocket.hxx"
-#include "util/Compiler.h"
 #include "util/IntrusiveList.hxx"
 
 #include <cstddef>
@@ -156,7 +155,7 @@ public:
 	 */
 	bool SendResponse() noexcept;
 
-	gcc_pure
+	[[gnu::pure]]
 	ssize_t GetBytesTillMetaData() const noexcept;
 
 	ssize_t TryWritePage(const Page &page, size_t position) noexcept;

src/output/plugins/httpd/HttpdInternal.hxx

@@ -17,7 +17,6 @@
 #include "event/ServerSocket.hxx"
 #include "event/InjectEvent.hxx"
 #include "util/Cast.hxx"
-#include "util/Compiler.h"
 #include "util/IntrusiveList.hxx"
 
 #include <queue>
@@ -173,7 +172,7 @@ public:
 	 *
 	 * Caller must lock the mutex.
 	 */
-	gcc_pure
+	[[gnu::pure]]
 	bool HasClients() const noexcept {
 		return !clients.empty();
 	}
@@ -181,7 +180,7 @@ public:
 	/**
 	 * Check whether there is at least one client.
 	 */
-	gcc_pure
+	[[gnu::pure]]
 	bool LockHasClients() const noexcept {
 		const std::scoped_lock<Mutex> protect(mutex);
 		return HasClients();
@@ -205,7 +204,7 @@ public:
 	 */
 	void SendHeader(HttpdClient &client) const noexcept;
 
-	gcc_pure
+	[[gnu::pure]]
 	std::chrono::steady_clock::duration Delay() const noexcept override;
 
 	/**