Vulkan:Level/Layer hash fix-up

Simplify has function for level/layer of imageView and add asserts to make sure that there won't be hash collisions. Bug: angleproject:4651 Change-Id: I8ab86a4f3d7aa668ad2c08e61bd5fd57744fcd12 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2257265Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Tobin Ehlis <tobine@google.com>

Vulkan:Level/Layer hash fix-up
cfbf769d · Tobin Ehlis · Commit Bot · 113c5e29 · cfbf769d
Commit cfbf769d authored Jun 22, 2020 by Tobin Ehlis Committed by Commit Bot Jun 22, 2020
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vk_cache_utils.h src/libANGLE/renderer/vulkan/vk_cache_utils.h +5 -3

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--- a/src/libANGLE/renderer/vulkan/vk_cache_utils.h
+++ b/src/libANGLE/renderer/vulkan/vk_cache_utils.h
@@ -883,9 +883,11 @@ struct hash<rx::vk::LayerLevel>
    size_t operator()(const rx::vk::LayerLevel &layerLevel) const
    {
        // The left-shift by 11 was found to produce unique hash values
-        // in a 256x256 space for layer/level
-        return std::hash<uint32_t>()(layerLevel.layer) ^
-               (std::hash<uint32_t>()(layerLevel.level) << 11);
+        // in a [0..1000][0..2048] space for layer/level
+        // Make sure that layer/level hash bits don't overlap or overflow
+        ASSERT((layerLevel.layer & 0x000007FF) == layerLevel.layer);
+        ASSERT((layerLevel.level & 0xFFE00000) == 0);
+        return layerLevel.layer | (layerLevel.level << 11);
    }
 };
 }  // namespace std