remove Buffer.sync_mapped_writes

`zero_init_needs_flush_now` was always equal to `mapping.is_coherent`
which is not correct but is fixed by the next commit.

wgpu-core/src/device/mod.rs

@@ -314,14 +314,11 @@ fn map_buffer<A: HalApi>(
             .map_err(DeviceError::from)?
     };
 
-    *buffer.sync_mapped_writes.lock() = match kind {
-        HostMap::Read if !mapping.is_coherent => unsafe {
+    if !mapping.is_coherent && kind == HostMap::Read {
+        unsafe {
             raw.invalidate_mapped_ranges(raw_buffer, iter::once(offset..offset + size));
-            None
-        },
-        HostMap::Write if !mapping.is_coherent => Some(offset..offset + size),
-        _ => None,
-    };
+        }
+    }
 
     assert_eq!(offset % wgt::COPY_BUFFER_ALIGNMENT, 0);
     assert_eq!(size % wgt::COPY_BUFFER_ALIGNMENT, 0);
@@ -339,9 +336,6 @@ fn map_buffer<A: HalApi>(
     // If this is a write mapping zeroing out the memory here is the only
     // reasonable way as all data is pushed to GPU anyways.
 
-    // No need to flush if it is flushed later anyways.
-    let zero_init_needs_flush_now =
-        mapping.is_coherent && buffer.sync_mapped_writes.lock().is_none();
     let mapped = unsafe { std::slice::from_raw_parts_mut(mapping.ptr.as_ptr(), size as usize) };
 
     for uninitialized in buffer
@@ -355,7 +349,7 @@ fn map_buffer<A: HalApi>(
             (uninitialized.start - offset) as usize..(uninitialized.end - offset) as usize;
         mapped[fill_range].fill(0);
 
-        if zero_init_needs_flush_now {
+        if mapping.is_coherent {
             unsafe { raw.flush_mapped_ranges(raw_buffer, iter::once(uninitialized)) };
         }
     }

wgpu-core/src/device/resource.rs

@@ -597,7 +597,6 @@ impl<A: HalApi> Device<A> {
                 rank::BUFFER_INITIALIZATION_STATUS,
                 BufferInitTracker::new(aligned_size),
             ),
-            sync_mapped_writes: Mutex::new(rank::BUFFER_SYNC_MAPPED_WRITES, None),
             map_state: Mutex::new(rank::BUFFER_MAP_STATE, resource::BufferMapState::Idle),
             label: desc.label.to_string(),
             tracking_data: TrackingData::new(self.tracker_indices.buffers.clone()),
@@ -697,7 +696,6 @@ impl<A: HalApi> Device<A> {
                 rank::BUFFER_INITIALIZATION_STATUS,
                 BufferInitTracker::new(0),
             ),
-            sync_mapped_writes: Mutex::new(rank::BUFFER_SYNC_MAPPED_WRITES, None),
             map_state: Mutex::new(rank::BUFFER_MAP_STATE, resource::BufferMapState::Idle),
             label: desc.label.to_string(),
             tracking_data: TrackingData::new(self.tracker_indices.buffers.clone()),

wgpu-core/src/lock/rank.rs

@@ -120,7 +120,6 @@ define_lock_ranks! {
 
     rank BUFFER_BIND_GROUPS "Buffer::bind_groups" followed by { }
     rank BUFFER_INITIALIZATION_STATUS "Buffer::initialization_status" followed by { }
-    rank BUFFER_SYNC_MAPPED_WRITES "Buffer::sync_mapped_writes" followed by { }
     rank DEVICE_DEFERRED_DESTROY "Device::deferred_destroy" followed by { }
     rank DEVICE_FENCE "Device::fence" followed by { }
     #[allow(dead_code)]

wgpu-core/src/resource.rs

@@ -431,7 +431,6 @@ pub struct Buffer<A: HalApi> {
     pub(crate) usage: wgt::BufferUsages,
     pub(crate) size: wgt::BufferAddress,
     pub(crate) initialization_status: RwLock<BufferInitTracker>,
-    pub(crate) sync_mapped_writes: Mutex<Option<hal::MemoryRange>>,
     /// The `label` from the descriptor used to create the resource.
     pub(crate) label: String,
     pub(crate) tracking_data: TrackingData,