diff --git a/LayoutTests/ChangeLog b/LayoutTests/ChangeLog
index 512e521..cfb54ec 100644
--- a/LayoutTests/ChangeLog
+++ b/LayoutTests/ChangeLog
@@ -1,3 +1,29 @@
+2019-05-11  Simon Fraser  <simon.fraser@apple.com>
+
+        Backing-sharing layers with transforms render incorrectly
+        https://bugs.webkit.org/show_bug.cgi?id=197692
+        <rdar://problem/50652127>
+
+        Reviewed by Antti Koivisto.
+        
+        Ref tests for effects on sharing layers. The references make "clipping" be stacking context via z-index,
+        which eliminates sharing.
+
+        * compositing/shared-backing/nested-shared-layers-with-opacity-expected.html: Added.
+        * compositing/shared-backing/nested-shared-layers-with-opacity.html: Added.
+        * compositing/shared-backing/shared-layer-has-blending-expected.html: Added.
+        * compositing/shared-backing/shared-layer-has-blending.html: Added.
+        * compositing/shared-backing/shared-layer-has-filter-expected.html: Added.
+        * compositing/shared-backing/shared-layer-has-filter.html: Added.
+        * compositing/shared-backing/shared-layer-has-opacity-expected.html: Added.
+        * compositing/shared-backing/shared-layer-has-opacity.html: Added.
+        * compositing/shared-backing/shared-layer-has-reflection-expected.html: Added.
+        * compositing/shared-backing/shared-layer-has-reflection.html: Added.
+        * compositing/shared-backing/shared-layer-has-transform-expected.html: Added.
+        * compositing/shared-backing/shared-layer-has-transform.html: Added.
+        * compositing/shared-backing/shared-layer-isolates-blending-expected.html: Added.
+        * compositing/shared-backing/shared-layer-isolates-blending.html: Added.
+
 2019-05-10  Zalan Bujtas  <zalan@apple.com>
 
         [iOS] baidu.com: Synthetic bold renders too far apart, appears doubled.
diff --git a/LayoutTests/compositing/shared-backing/nested-shared-layers-with-opacity-expected.html b/LayoutTests/compositing/shared-backing/nested-shared-layers-with-opacity-expected.html
new file mode 100644
index 0000000..75547c3
--- /dev/null
+++ b/LayoutTests/compositing/shared-backing/nested-shared-layers-with-opacity-expected.html
@@ -0,0 +1,51 @@
+<!DOCTYPE html>
+<html>
+<head>
+    <title>Tests painting of a layer with opacity into shared backing</title>
+    <style>
+        .clipping {
+            position: absolute;
+            z-index: 0;
+            top: 20px;
+            left: 20px;
+            overflow: hidden;
+            height: 300px;
+            width: 300px;
+            margin: 10px;
+            border: 1px solid black;
+        }
+
+		.box {
+			position: relative;
+			top: 50px;
+			left: 50px;
+            width: 180px;
+            height: 180px;
+            background-color: green;
+		}
+		
+		.opacity {
+            opacity: 0.5;
+		}
+    
+        .composited {
+            transform: translateZ(0);
+        }
+        
+        .trigger {
+            width: 50px;
+            height: 50px;
+            background-color: silver;
+        }
+        
+    </style>
+</head>
+<body>
+    <div class="composited trigger"></div>
+    <div class="clipping">
+        <div class="sharing opacity box">
+			<div class="opacity box"></div>
+        </div>
+    </div>
+</body>
+</html>
diff --git a/LayoutTests/compositing/shared-backing/nested-shared-layers-with-opacity.html b/LayoutTests/compositing/shared-backing/nested-shared-layers-with-opacity.html
new file mode 100644
index 0000000..fa947f2
--- /dev/null
+++ b/LayoutTests/compositing/shared-backing/nested-shared-layers-with-opacity.html
@@ -0,0 +1,50 @@
+<!DOCTYPE html>
+<html>
+<head>
+    <title>Tests painting of a layer with opacity into shared backing</title>
+    <style>
+        .clipping {
+            position: absolute;
+            top: 20px;
+            left: 20px;
+            overflow: hidden;
+            height: 300px;
+            width: 300px;
+            margin: 10px;
+            border: 1px solid black;
+        }
+
+		.box {
+			position: relative;
+			top: 50px;
+			left: 50px;
+            width: 180px;
+            height: 180px;
+            background-color: green;
+		}
+		
+		.opacity {
+            opacity: 0.5;
+		}
+    
+        .composited {
+            transform: translateZ(0);
+        }
+        
+        .trigger {
+            width: 50px;
+            height: 50px;
+            background-color: silver;
+        }
+        
+    </style>
+</head>
+<body>
+    <div class="composited trigger"></div>
+    <div class="clipping">
+        <div class="sharing opacity box">
+			<div class="opacity box"></div>
+        </div>
+    </div>
+</body>
+</html>
diff --git a/LayoutTests/compositing/shared-backing/shared-layer-has-blending-expected.html b/LayoutTests/compositing/shared-backing/shared-layer-has-blending-expected.html
new file mode 100644
index 0000000..8f47023
--- /dev/null
+++ b/LayoutTests/compositing/shared-backing/shared-layer-has-blending-expected.html
@@ -0,0 +1,46 @@
+<!DOCTYPE html>
+<html>
+<head>
+    <style>
+        .clipping {
+            position: absolute;
+            z-index: 0;
+            top: 20px;
+            left: 20px;
+            overflow: hidden;
+            height: 300px;
+            width: 300px;
+            margin: 10px;
+            border: 1px solid black;
+        }
+        
+        .sharing {
+			position: relative;
+			top: 50px;
+			left: 50px;
+            width: 180px;
+            height: 180px;
+            background-color: green;
+        }
+        
+        .blending {
+            mix-blend-mode: difference;
+        }
+
+        .trigger {
+            transform: translateZ(0);
+            width: 50px;
+            height: 50px;
+            background-color: silver;
+        }
+        
+    </style>
+</head>
+<body>
+    <div class="composited trigger"></div>
+    <div class="clipping">
+        <div class="sharing blending box">
+        </div>
+    </div>
+</body>
+</html>
diff --git a/LayoutTests/compositing/shared-backing/shared-layer-has-blending.html b/LayoutTests/compositing/shared-backing/shared-layer-has-blending.html
new file mode 100644
index 0000000..483240c
--- /dev/null
+++ b/LayoutTests/compositing/shared-backing/shared-layer-has-blending.html
@@ -0,0 +1,46 @@
+<!DOCTYPE html>
+<html>
+<head>
+    <title>Tests painting of a layer with mix-blend-mode into shared backing</title>
+    <style>
+        .clipping {
+            position: absolute;
+            top: 20px;
+            left: 20px;
+            overflow: hidden;
+            height: 300px;
+            width: 300px;
+            margin: 10px;
+            border: 1px solid black;
+        }
+        
+        .sharing {
+			position: relative;
+			top: 50px;
+			left: 50px;
+            width: 180px;
+            height: 180px;
+            background-color: green;
+        }
+        
+        .blending {
+            mix-blend-mode: difference;
+        }
+
+        .trigger {
+            transform: translateZ(0);
+            width: 50px;
+            height: 50px;
+            background-color: silver;
+        }
+        
+    </style>
+</head>
+<body>
+    <div class="composited trigger"></div>
+    <div class="clipping">
+        <div class="sharing blending box">
+        </div>
+    </div>
+</body>
+</html>
diff --git a/LayoutTests/compositing/shared-backing/shared-layer-has-filter-expected.html b/LayoutTests/compositing/shared-backing/shared-layer-has-filter-expected.html
new file mode 100644
index 0000000..9d38f9b
--- /dev/null
+++ b/LayoutTests/compositing/shared-backing/shared-layer-has-filter-expected.html
@@ -0,0 +1,46 @@
+<!DOCTYPE html>
+<html>
+<head>
+    <style>
+        .clipping {
+            position: absolute;
+            z-index: 0;
+            top: 20px;
+            left: 20px;
+            overflow: hidden;
+            height: 300px;
+            width: 300px;
+            margin: 10px;
+            border: 1px solid black;
+        }
+        
+        .sharing {
+			position: relative;
+			top: 50px;
+			left: 50px;
+            width: 180px;
+            height: 180px;
+            background-color: green;
+        }
+        
+        .filtered {
+            filter: saturate(0);
+        }
+
+        .trigger {
+            transform: translateZ(0);
+            width: 50px;
+            height: 50px;
+            background-color: silver;
+        }
+        
+    </style>
+</head>
+<body>
+    <div class="composited trigger"></div>
+    <div class="clipping">
+        <div class="sharing filtered box">
+        </div>
+    </div>
+</body>
+</html>
diff --git a/LayoutTests/compositing/shared-backing/shared-layer-has-filter.html b/LayoutTests/compositing/shared-backing/shared-layer-has-filter.html
new file mode 100644
index 0000000..7b7a01e
--- /dev/null
+++ b/LayoutTests/compositing/shared-backing/shared-layer-has-filter.html
@@ -0,0 +1,46 @@
+<!DOCTYPE html>
+<html>
+<head>
+    <title>Tests painting of a layer with a filter into shared backing</title>
+    <style>
+        .clipping {
+            position: absolute;
+            top: 20px;
+            left: 20px;
+            overflow: hidden;
+            height: 300px;
+            width: 300px;
+            margin: 10px;
+            border: 1px solid black;
+        }
+        
+        .sharing {
+			position: relative;
+			top: 50px;
+			left: 50px;
+            width: 180px;
+            height: 180px;
+            background-color: green;
+        }
+        
+        .filtered {
+            filter: saturate(0);
+        }
+
+        .trigger {
+            transform: translateZ(0);
+            width: 50px;
+            height: 50px;
+            background-color: silver;
+        }
+        
+    </style>
+</head>
+<body>
+    <div class="composited trigger"></div>
+    <div class="clipping">
+        <div class="sharing filtered box">
+        </div>
+    </div>
+</body>
+</html>
diff --git a/LayoutTests/compositing/shared-backing/shared-layer-has-opacity-expected.html b/LayoutTests/compositing/shared-backing/shared-layer-has-opacity-expected.html
new file mode 100644
index 0000000..faf3306
--- /dev/null
+++ b/LayoutTests/compositing/shared-backing/shared-layer-has-opacity-expected.html
@@ -0,0 +1,47 @@
+<!DOCTYPE html>
+<html>
+<head>
+    <title>Tests painting of a layer with opacity into shared backing</title>
+    <style>
+        .clipping {
+            position: absolute;
+            z-index: 0;
+            top: 20px;
+            left: 20px;
+            overflow: hidden;
+            height: 300px;
+            width: 300px;
+            margin: 10px;
+            border: 1px solid black;
+        }
+        
+        .sharing {
+			position: relative;
+			top: 50px;
+			left: 50px;
+            width: 180px;
+            height: 180px;
+            background-color: green;
+        }
+        
+        .opacity {
+            opacity: 0.5;
+        }
+
+        .trigger {
+            transform: translateZ(0);
+            width: 50px;
+            height: 50px;
+            background-color: silver;
+        }
+        
+    </style>
+</head>
+<body>
+    <div class="composited trigger"></div>
+    <div class="clipping">
+        <div class="sharing opacity box">
+        </div>
+    </div>
+</body>
+</html>
diff --git a/LayoutTests/compositing/shared-backing/shared-layer-has-opacity.html b/LayoutTests/compositing/shared-backing/shared-layer-has-opacity.html
new file mode 100644
index 0000000..0143d8f
--- /dev/null
+++ b/LayoutTests/compositing/shared-backing/shared-layer-has-opacity.html
@@ -0,0 +1,46 @@
+<!DOCTYPE html>
+<html>
+<head>
+    <title>Tests painting of a layer with opacity into shared backing</title>
+    <style>
+        .clipping {
+            position: absolute;
+            top: 20px;
+            left: 20px;
+            overflow: hidden;
+            height: 300px;
+            width: 300px;
+            margin: 10px;
+            border: 1px solid black;
+        }
+        
+        .sharing {
+			position: relative;
+			top: 50px;
+			left: 50px;
+            width: 180px;
+            height: 180px;
+            background-color: green;
+        }
+        
+        .opacity {
+            opacity: 0.5;
+        }
+
+        .trigger {
+            transform: translateZ(0);
+            width: 50px;
+            height: 50px;
+            background-color: silver;
+        }
+        
+    </style>
+</head>
+<body>
+    <div class="composited trigger"></div>
+    <div class="clipping">
+        <div class="sharing opacity box">
+        </div>
+    </div>
+</body>
+</html>
diff --git a/LayoutTests/compositing/shared-backing/shared-layer-has-reflection-expected.html b/LayoutTests/compositing/shared-backing/shared-layer-has-reflection-expected.html
new file mode 100644
index 0000000..8be25b2
--- /dev/null
+++ b/LayoutTests/compositing/shared-backing/shared-layer-has-reflection-expected.html
@@ -0,0 +1,47 @@
+<!DOCTYPE html>
+<html>
+<head>
+    <style>
+        .clipping {
+            position: absolute;
+            z-index: 0;
+            top: 20px;
+            left: 20px;
+            overflow: hidden;
+            height: 300px;
+            width: 300px;
+            margin: 10px;
+            border: 1px solid black;
+        }
+        
+        .sharing {
+			position: relative;
+			top: 50px;
+			left: 50px;
+            width: 180px;
+            height: 160px;
+            background-color: green;
+            border-bottom: 20px solid orange;
+        }
+        
+        .reflected {
+            -webkit-box-reflect: below 10px;
+        }
+
+        .trigger {
+            transform: translateZ(0);
+            width: 50px;
+            height: 50px;
+            background-color: silver;
+        }
+        
+    </style>
+</head>
+<body>
+    <div class="composited trigger"></div>
+    <div class="clipping">
+        <div class="sharing reflected box">
+        </div>
+    </div>
+</body>
+</html>
diff --git a/LayoutTests/compositing/shared-backing/shared-layer-has-reflection.html b/LayoutTests/compositing/shared-backing/shared-layer-has-reflection.html
new file mode 100644
index 0000000..9872332
--- /dev/null
+++ b/LayoutTests/compositing/shared-backing/shared-layer-has-reflection.html
@@ -0,0 +1,47 @@
+<!DOCTYPE html>
+<html>
+<head>
+    <title>Tests painting of a layer with a reflection into shared backing</title>
+    <style>
+        .clipping {
+            position: absolute;
+            top: 20px;
+            left: 20px;
+            overflow: hidden;
+            height: 300px;
+            width: 300px;
+            margin: 10px;
+            border: 1px solid black;
+        }
+        
+        .sharing {
+			position: relative;
+			top: 50px;
+			left: 50px;
+            width: 180px;
+            height: 160px;
+            background-color: green;
+            border-bottom: 20px solid orange;
+        }
+        
+        .reflected {
+            -webkit-box-reflect: below 10px;
+        }
+
+        .trigger {
+            transform: translateZ(0);
+            width: 50px;
+            height: 50px;
+            background-color: silver;
+        }
+        
+    </style>
+</head>
+<body>
+    <div class="composited trigger"></div>
+    <div class="clipping">
+        <div class="sharing reflected box">
+        </div>
+    </div>
+</body>
+</html>
diff --git a/LayoutTests/compositing/shared-backing/shared-layer-has-transform-expected.html b/LayoutTests/compositing/shared-backing/shared-layer-has-transform-expected.html
new file mode 100644
index 0000000..82c0710
--- /dev/null
+++ b/LayoutTests/compositing/shared-backing/shared-layer-has-transform-expected.html
@@ -0,0 +1,46 @@
+<!DOCTYPE html>
+<html>
+<head>
+    <style>
+        .clipping {
+            position: absolute;
+            z-index: 0;
+            top: 20px;
+            left: 20px;
+            overflow: hidden;
+            height: 300px;
+            width: 300px;
+            margin: 10px;
+            border: 1px solid black;
+        }
+        
+        .sharing {
+			position: relative;
+			top: 50px;
+			left: 50px;
+            width: 180px;
+            height: 180px;
+            background-color: green;
+        }
+        
+        .transformed {
+            transform: rotate(45deg);
+        }
+
+        .trigger {
+            transform: translateZ(0);
+            width: 50px;
+            height: 50px;
+            background-color: silver;
+        }
+        
+    </style>
+</head>
+<body>
+    <div class="composited trigger"></div>
+    <div class="clipping">
+        <div class="sharing transformed box">
+        </div>
+    </div>
+</body>
+</html>
diff --git a/LayoutTests/compositing/shared-backing/shared-layer-has-transform.html b/LayoutTests/compositing/shared-backing/shared-layer-has-transform.html
new file mode 100644
index 0000000..44d8ccd
--- /dev/null
+++ b/LayoutTests/compositing/shared-backing/shared-layer-has-transform.html
@@ -0,0 +1,46 @@
+<!DOCTYPE html>
+<html>
+<head>
+    <title>Tests painting of a layer with a transform into shared backing</title>
+    <style>
+        .clipping {
+            position: absolute;
+            top: 20px;
+            left: 20px;
+            overflow: hidden;
+            height: 300px;
+            width: 300px;
+            margin: 10px;
+            border: 1px solid black;
+        }
+        
+        .sharing {
+			position: relative;
+			top: 50px;
+			left: 50px;
+            width: 180px;
+            height: 180px;
+            background-color: green;
+        }
+        
+        .transformed {
+            transform: rotate(45deg);
+        }
+
+        .trigger {
+            transform: translateZ(0);
+            width: 50px;
+            height: 50px;
+            background-color: silver;
+        }
+        
+    </style>
+</head>
+<body>
+    <div class="composited trigger"></div>
+    <div class="clipping">
+        <div class="sharing transformed box">
+        </div>
+    </div>
+</body>
+</html>
diff --git a/LayoutTests/compositing/shared-backing/shared-layer-isolates-blending-expected.html b/LayoutTests/compositing/shared-backing/shared-layer-isolates-blending-expected.html
new file mode 100644
index 0000000..cffc6a8
--- /dev/null
+++ b/LayoutTests/compositing/shared-backing/shared-layer-isolates-blending-expected.html
@@ -0,0 +1,56 @@
+<!DOCTYPE html>
+<html>
+<head>
+    <style>
+        .clipping {
+            position: absolute;
+            z-index: 0;
+            top: 20px;
+            left: 20px;
+            overflow: hidden;
+            height: 300px;
+            width: 300px;
+            margin: 10px;
+            border: 1px solid black;
+        }
+        
+        .sharing {
+			position: relative;
+			top: 30px;
+			left: 30px;
+            width: 180px;
+            height: 180px;
+            background-color: green;
+        }
+        
+        .isolation {
+            isolation: isolate;
+        }
+        
+        .blending {
+            position: relative;
+            top: 50px;
+            left: 50px;
+            width: 180px;
+            height: 180px;
+            mix-blend-mode: multiply;
+            background-color: green;
+        }
+
+        .trigger {
+            transform: translateZ(0);
+            width: 50px;
+            height: 50px;
+            background-color: silver;
+        }
+    </style>
+</head>
+<body>
+    <div class="composited trigger"></div>
+    <div class="clipping">
+        <div class="sharing isolation box">
+            <div class="blending"></div>
+        </div>
+    </div>
+</body>
+</html>
diff --git a/LayoutTests/compositing/shared-backing/shared-layer-isolates-blending.html b/LayoutTests/compositing/shared-backing/shared-layer-isolates-blending.html
new file mode 100644
index 0000000..0a77c83
--- /dev/null
+++ b/LayoutTests/compositing/shared-backing/shared-layer-isolates-blending.html
@@ -0,0 +1,56 @@
+<!DOCTYPE html>
+<html>
+<head>
+    <title>Tests painting of a layer which isolates blending into shared backing</title>
+    <style>
+        .clipping {
+            position: absolute;
+            top: 20px;
+            left: 20px;
+            overflow: hidden;
+            height: 300px;
+            width: 300px;
+            margin: 10px;
+            border: 1px solid black;
+        }
+        
+        .sharing {
+			position: relative;
+			top: 30px;
+			left: 30px;
+            width: 180px;
+            height: 180px;
+            background-color: green;
+        }
+        
+        .isolation {
+            isolation: isolate;
+        }
+        
+        .blending {
+            position: relative;
+            top: 50px;
+            left: 50px;
+            width: 180px;
+            height: 180px;
+            mix-blend-mode: multiply;
+            background-color: green;
+        }
+
+        .trigger {
+            transform: translateZ(0);
+            width: 50px;
+            height: 50px;
+            background-color: silver;
+        }
+    </style>
+</head>
+<body>
+    <div class="composited trigger"></div>
+    <div class="clipping">
+        <div class="sharing isolation box">
+            <div class="blending"></div>
+        </div>
+    </div>
+</body>
+</html>
diff --git a/Source/WebCore/ChangeLog b/Source/WebCore/ChangeLog
index 08adb42..d53874b 100644
--- a/Source/WebCore/ChangeLog
+++ b/Source/WebCore/ChangeLog
@@ -1,3 +1,62 @@
+2019-05-11  Simon Fraser  <simon.fraser@apple.com>
+
+        Backing-sharing layers with transforms render incorrectly
+        https://bugs.webkit.org/show_bug.cgi?id=197692
+        <rdar://problem/50652127>
+
+        Reviewed by Antti Koivisto.
+
+        Layers that paint into shared backing need to enter the RenderLayer painting code
+        in a way that paints the filters, transforms, opacity and blending.
+        
+        RenderLayerBacking::paintIntoLayer() normally enters at paintLayerContents(), because
+        the effects are rendered via the GraphicsLayer, but shared layers will paint effects.
+        Note that if the backing-provider has effects, it will be the stacking context
+        for the shared layers, so it's correct that sharing layers are impacted by effects
+        on the backing-provider.
+
+        In addition, we have to ensure that we don't over-eagerly make layers shared.
+        Consider:
+        
+        <div class="clipping">
+            <div class="sharing">
+                <div class="inner">
+                </div>
+            </div>
+        </div>
+        
+        Here "clipping" is the provider layer, "sharing" paints into shared backing, but
+        we don't want to also mark "inner" as sharing, since "sharing" will just paint it.
+        This is akin to avoiding unnecessary compositing of z-order descendants when they can just
+        paint.
+        
+        To do this we need to ensure that sharing layers are treated like compositing layers
+        in the overlap map, i.e. when a layer is sharing, we call overlapMap.pushCompositingContainer(),
+        and later overlapMap.popCompositingContainer().
+
+        Tests: compositing/shared-backing/nested-shared-layers-with-opacity.html
+               compositing/shared-backing/shared-layer-has-blending.html
+               compositing/shared-backing/shared-layer-has-filter.html
+               compositing/shared-backing/shared-layer-has-opacity.html
+               compositing/shared-backing/shared-layer-has-reflection.html
+               compositing/shared-backing/shared-layer-has-transform.html
+               compositing/shared-backing/shared-layer-isolates-blending.html
+               compositing/shared-backing/shared-transformed-layer-bounds.html
+               compositing/shared-backing/sharing-layer-becomes-non-scrollable.html
+               compositing/shared-backing/sharing-layer-has-effect.html
+
+        * rendering/RenderLayer.cpp:
+        (WebCore::RenderLayer::paintLayer):
+        (WebCore::RenderLayer::paintLayerWithEffects):
+        * rendering/RenderLayer.h:
+        * rendering/RenderLayerBacking.cpp:
+        (WebCore::RenderLayerBacking::paintIntoLayer):
+        * rendering/RenderLayerCompositor.cpp:
+        (WebCore::RenderLayerCompositor::CompositingState::stateForPaintOrderChildren const):
+        (WebCore::backingProviderLayerCanIncludeLayer):
+        (WebCore::RenderLayerCompositor::computeCompositingRequirements):
+        (WebCore::RenderLayerCompositor::traverseUnchangedSubtree):
+
 2019-05-10  Youenn Fablet  <youenn@apple.com>
 
         A service worker instance should be terminated when its SWServer is destroyed
diff --git a/Source/WebCore/rendering/RenderLayer.cpp b/Source/WebCore/rendering/RenderLayer.cpp
index b062d0b..185a875 100644
--- a/Source/WebCore/rendering/RenderLayer.cpp
+++ b/Source/WebCore/rendering/RenderLayer.cpp
@@ -4100,13 +4100,18 @@
         return;
     }
 
+    paintLayerWithEffects(context, paintingInfo, paintFlags);
+}
+
+void RenderLayer::paintLayerWithEffects(GraphicsContext& context, const LayerPaintingInfo& paintingInfo, OptionSet<PaintLayerFlag> paintFlags)
+{
     // Non self-painting leaf layers don't need to be painted as their renderer() should properly paint itself.
     if (!isSelfPaintingLayer() && !hasSelfPaintingLayerDescendant())
         return;
 
     if (shouldSuppressPaintingLayer(this))
         return;
-    
+
     // If this layer is totally invisible then there is nothing to paint.
     if (!renderer().opacity())
         return;
diff --git a/Source/WebCore/rendering/RenderLayer.h b/Source/WebCore/rendering/RenderLayer.h
index da4beb9..22be9bc 100644
--- a/Source/WebCore/rendering/RenderLayer.h
+++ b/Source/WebCore/rendering/RenderLayer.h
@@ -1003,6 +1003,8 @@
     void applyFilters(GraphicsContext& originalContext, const LayerPaintingInfo&, const LayerFragments&);
 
     void paintLayer(GraphicsContext&, const LayerPaintingInfo&, OptionSet<PaintLayerFlag>);
+    void paintLayerWithEffects(GraphicsContext&, const LayerPaintingInfo&, OptionSet<PaintLayerFlag>);
+
     void paintLayerContentsAndReflection(GraphicsContext&, const LayerPaintingInfo&, OptionSet<PaintLayerFlag>);
     void paintLayerByApplyingTransform(GraphicsContext&, const LayerPaintingInfo&, OptionSet<PaintLayerFlag>, const LayoutSize& translationOffset = LayoutSize());
     void paintLayerContents(GraphicsContext&, const LayerPaintingInfo&, OptionSet<PaintLayerFlag>);
diff --git a/Source/WebCore/rendering/RenderLayerBacking.cpp b/Source/WebCore/rendering/RenderLayerBacking.cpp
index 35a14c1..c3fcb9f 100644
--- a/Source/WebCore/rendering/RenderLayerBacking.cpp
+++ b/Source/WebCore/rendering/RenderLayerBacking.cpp
@@ -2668,10 +2668,13 @@
 
         RenderLayer::LayerPaintingInfo paintingInfo(&m_owningLayer, paintDirtyRect, paintBehavior, -m_subpixelOffsetFromRenderer);
 
-        layer.paintLayerContents(context, paintingInfo, paintFlags);
+        if (&layer == &m_owningLayer) {
+            layer.paintLayerContents(context, paintingInfo, paintFlags);
 
-        if (layer.containsDirtyOverlayScrollbars())
-            layer.paintLayerContents(context, paintingInfo, paintFlags | RenderLayer::PaintLayerPaintingOverlayScrollbars);
+            if (layer.containsDirtyOverlayScrollbars())
+                layer.paintLayerContents(context, paintingInfo, paintFlags | RenderLayer::PaintLayerPaintingOverlayScrollbars);
+        } else
+            layer.paintLayerWithEffects(context, paintingInfo, paintFlags);
 
         if (layer.isRenderViewLayer())
             renderer().view().frameView().didPaintContents(context, paintDirtyRect, paintingState);
diff --git a/Source/WebCore/rendering/RenderLayerCompositor.cpp b/Source/WebCore/rendering/RenderLayerCompositor.cpp
index 790791b..ca5424e 100644
--- a/Source/WebCore/rendering/RenderLayerCompositor.cpp
+++ b/Source/WebCore/rendering/RenderLayerCompositor.cpp
@@ -241,6 +241,7 @@
         else
             childState.stackingContextAncestor = stackingContextAncestor;
 
+        childState.backingSharingAncestor = backingSharingAncestor;
         childState.subtreeIsCompositing = false;
         childState.testingOverlap = testingOverlap;
         childState.fullPaintOrderTraversalRequired = fullPaintOrderTraversalRequired;
@@ -268,6 +269,7 @@
     }
 
     RenderLayer* compositingAncestor;
+    RenderLayer* backingSharingAncestor { nullptr };
     RenderLayer* stackingContextAncestor { nullptr };
     bool subtreeIsCompositing { false };
     bool testingOverlap { true };
@@ -860,6 +862,10 @@
 
 static bool backingProviderLayerCanIncludeLayer(const RenderLayer& sharedLayer, const RenderLayer& layer)
 {
+    // Disable sharing when painting shared layers doesn't work correctly.
+    if (layer.hasReflection())
+        return false;
+
     return layer.ancestorLayerIsInContainingBlockChain(sharedLayer);
 }
 
@@ -981,6 +987,9 @@
         // Compositing for any reason disables backing sharing.
         LOG_WITH_STREAM(Compositing, stream << &layer << " is compositing - flushing sharing to " << backingSharingState.backingProviderCandidate << " with " << backingSharingState.backingSharingLayers.size() << " sharing layers");
         backingSharingState.resetBackingProviderCandidate();
+    } else if (layerPaintsIntoProvidedBacking) {
+        childState.backingSharingAncestor = &layer;
+        overlapMap.pushCompositingContainer();
     }
 
 #if !ASSERT_DISABLED
@@ -1064,7 +1073,7 @@
         compositingState.hasNotIsolatedCompositedBlendingDescendants = true;
 #endif
 
-    if (childState.compositingAncestor == &layer && !layer.isRenderViewLayer())
+    if ((childState.compositingAncestor == &layer && !layer.isRenderViewLayer()) || childState.backingSharingAncestor == &layer)
         overlapMap.popCompositingContainer();
 
     // If we're back at the root, and no other layers need to be composited, and the root layer itself doesn't need
@@ -1228,7 +1237,7 @@
         compositingState.hasNotIsolatedCompositedBlendingDescendants = true;
 #endif
 
-    if (childState.compositingAncestor == &layer && !layer.isRenderViewLayer())
+    if ((childState.compositingAncestor == &layer && !layer.isRenderViewLayer()) || childState.backingSharingAncestor == &layer)
         overlapMap.popCompositingContainer();
 
     if (layer.isComposited())