ch10a README

6 files changed, 284 insertions, 4 deletions

diff --git a/chapter10a/README.md b/chapter10a/README.md
index 6f51df28..968180b5 100644
--- a/chapter10a/README.md
+++ b/chapter10a/README.md
@@ -271,10 +271,28 @@ To enable this behaviour, we make the following enhancements.
 ## Local memory optimizations
 
 A load immediately following a store to the **same pointer and field** can use
-the stored value. A store immediately following another store to the same
-address can discard the earlier store when no other user needs it. Both the
-pointer and field checks matter: two different fields of one object are
-different addresses, as are the same fields of two different objects.
+the stored value. We just wrote `arg` into `p.x`, so reading it back needs no
+memory access:
+
+```java
+struct Box { int x; }
+Box p = new Box;
+p.x = arg;
+return p.x;  // Can return arg directly.
+```
+
+| Before: read back the stored value | After: use the value directly |
+|---|---|
+| ![Before: Return reads Load p.x after Store p.x](docs/load-after-store-before.svg) | ![After: Return uses arg and still consumes the Store's memory](docs/load-after-store-after.svg) |
+
+Return's result input changes from the Load to `arg`, and the unused Load
+disappears.  Return still consumes the Store's memory, so the write is retained.
+
+A store immediately following another store to the same address can also
+discard the earlier store when no other user needs it. That separate rewrite
+can remove the zero-initialization store still shown above. Both the pointer
+and field checks matter: two different fields of one object are different
+addresses, as are the same fields of two different objects.
 
 A load can also move up through a memory Phi. This extends
 [Chapter 5's push-through-Phi optimization](../chapter05/README.md#pushing-addition-up-through-a-phi):
diff --git a/chapter10a/docs/load-after-store-after.json b/chapter10a/docs/load-after-store-after.json
new file mode 100644
index 00000000..0f0d3a93
--- /dev/null
+++ b/chapter10a/docs/load-after-store-after.json
@@ -0,0 +1,20 @@
+{
+  "ver": 1,
+  "comp": "load-after-store-after",
+  "step": 1,
+  "roots": [10],
+  "scope": 0,
+  "nodes": [
+    {"id": 1, "label": "Start", "type": null, "kind": "CTRL", "edges": [], "proj": null},
+    {"id": 2, "label": "$ctrl", "type": null, "kind": "CTRL", "edges": [{"idx": 0, "def": 1, "role": "CTRL", "label": null}], "proj": {"par": 1, "idx": 0}},
+    {"id": 3, "label": "$mem", "type": null, "kind": "MEM", "edges": [{"idx": 0, "def": 1, "role": "MEM", "label": null}], "proj": {"par": 1, "idx": 1}},
+    {"id": 4, "label": "arg", "type": null, "kind": "DATA", "edges": [{"idx": 0, "def": 1, "role": "DATA", "label": null}], "proj": {"par": 1, "idx": 2}},
+    {"id": 5, "label": "new Box", "type": null, "kind": "DATA", "edges": [{"idx": 0, "def": 2, "role": "CTRL", "label": null}], "proj": null},
+    {"id": 6, "label": "#0", "type": null, "kind": "DATA", "edges": [{"idx": 0, "def": 1, "role": "ASSOC", "label": null}], "proj": null},
+    {"id": 7, "label": "Store p.x", "type": null, "kind": "MEM", "edges": [{"idx": 0, "def": 0, "role": "CTRL", "label": null}, {"idx": 1, "def": 3, "role": "MEM", "label": null}, {"idx": 2, "def": 5, "role": "DATA", "label": null}, {"idx": 3, "def": 6, "role": "DATA", "label": null}], "proj": null},
+    {"id": 8, "label": "Store p.x", "type": null, "kind": "MEM", "edges": [{"idx": 0, "def": 0, "role": "CTRL", "label": null}, {"idx": 1, "def": 7, "role": "MEM", "label": null}, {"idx": 2, "def": 5, "role": "DATA", "label": null}, {"idx": 3, "def": 4, "role": "DATA", "label": null}], "proj": null},
+    {"id": 10, "label": "Return", "type": null, "kind": "CTRL", "edges": [{"idx": 0, "def": 2, "role": "CTRL", "label": null}, {"idx": 1, "def": 8, "role": "MEM", "label": null}, {"idx": 2, "def": 4, "role": "DATA", "label": null}], "proj": null}
+  ],
+  "groups": [
+  ]
+}
diff --git a/chapter10a/docs/load-after-store-after.svg b/chapter10a/docs/load-after-store-after.svg
new file mode 100644
index 00000000..ee6d8189
--- /dev/null
+++ b/chapter10a/docs/load-after-store-after.svg
@@ -0,0 +1,101 @@
+<svg aria-label="Compiler graph" width="414" height="558" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 414 558" style="font-family: sans-serif;"><style>
+    html, body { height:100%; margin:0; font-family:sans-serif; }
+    .viewer { height:100%; display:grid; grid-template-rows:auto minmax(0,1fr) auto; }
+    .source { padding:8px; border-bottom:1px solid #ccc; }
+    #program { width:min(600px,80vw); vertical-align:middle; }
+    #status { margin-top:4px; }
+    #graph { min-height:0; overflow:hidden; position:relative; background:#fafbfc; }
+    #elk { width:100%; height:100%; }
+    #graph svg { display:block; }
+    .tools { display:flex; flex-wrap:wrap; align-items:center; gap:14px; margin-top:8px; font-size:12px; }
+    .hint { color:#616c78; }
+    .ctrl { color:#b63838; } .mem { color:#2867b2; } .data { color:#536477; }
+    .edge { fill:none; stroke-width:1.5; }
+    .edge.CTRL { stroke-width:2; }
+    .edge.ASSOC { stroke-dasharray:4 4; }
+    .edge.PARSER { stroke-dasharray:5 4; }
+    .parser rect { fill:#f6f0ff; stroke:#7956a5; stroke-width:1.5; stroke-dasharray:5 4; }
+    .edge.selected { stroke-width:3.5; }
+    .edge.bundle { stroke-width:4; }
+    .edge.bundle.selected { stroke-width:6; }
+    .edge-hit { fill:none; stroke:transparent; stroke-width:12; vector-effect:non-scaling-stroke; pointer-events:stroke; cursor:pointer; }
+    .edge-jump { fill:transparent; pointer-events:all; cursor:pointer; }
+    .node { cursor:pointer; }
+    .box { stroke:#758191; stroke-width:1; }
+    .node.held .box { stroke-dasharray:5 3; }
+    .node.near .box { stroke:#c18221; stroke-width:2; }
+    .node.focus .box { stroke:#9c4900; stroke-width:3; }
+    .node.selected .box { stroke:#1569b9; stroke-width:3; }
+    .node.folded .box { stroke-width:4; }
+    .node.folding .box { fill:#f4ccd7; }
+    .fold-tag { font-size:9px; font-weight:700; fill:#963751; }
+    .peep-area { fill:#fff3d9; fill-opacity:.8; stroke:#c18221; stroke-width:2; pointer-events:none; }
+    .node.peep-edit .box { stroke:#9c4900; stroke-width:3; }
+    .node.error .box { stroke:#b42318; stroke-width:4; }
+    #event.error { color:#b42318; font-weight:600; white-space:pre-wrap; overflow-wrap:anywhere; }
+    .peep-ghosts { pointer-events:none; }
+    .region-box { stroke:#9da9b8; stroke-width:1.5; }
+    .fold-btn { cursor:pointer; }
+    .fold-btn rect { fill:white; stroke:#596674; }
+    .fold-btn text { font-size:14px; fill:#152330; }
+    .fold-btn:focus rect { stroke:#1569b9; stroke-width:2; }
+    .shortcut { cursor:pointer; }
+    .shortcut path { fill:none; stroke-width:1.5; }
+    .shortcut rect { fill:#fff8ec; stroke:#b63838; stroke-dasharray:3 2; }
+    .shortcut text { font-size:11px; fill:#783030; }
+    .shortcut.selected rect, .shortcut:focus rect { stroke-width:2.5; }
+    .label { font-size:12px; fill:#152330; font-weight:600; }
+    .node-id { font-size:10px; fill:#596674; font-weight:400; }
+    .type { font-size:11px; fill:#455768; }
+    .port { stroke:#536477; stroke-width:1; }
+    .row { stroke:#b6afcf; stroke-width:1; }
+    .bind { font-size:12px; fill:#152330; }
+    .slot { font-size:10px; fill:#364352; paint-order:stroke; stroke:#fafbfc; stroke-width:3; }
+    #detail { position:absolute; top:8px; right:8px; margin:0; padding:12px; max-width:320px;
+      max-height:45%; overflow:auto; white-space:pre-wrap; overflow-wrap:anywhere;
+      background:#fffffff2; border:1px solid #bac5d0; border-radius:4px; font-size:12px; }
+    .controls { display:flex; flex-wrap:wrap; justify-content:center; align-items:center; gap:6px; padding:6px; }
+    .button { color:white; background:black; font-size:20px; min-width:30px; }
+    .button:disabled { background:grey; }
+    .count { font-size:20px; min-width:35px; text-align:center; }
+    #N { width:6ch; }
+    #scrub { width:clamp(120px,35vw,600px); }
+  </style><defs><marker id="arrow-CTRL" viewBox="0 -4 8 8" refX="8" refY="0" markerWidth="7" markerHeight="7" orient="auto-start-reverse"><path d="M0,-4L8,0L0,4Z" fill="#b63838"/></marker><marker id="arrow-DATA" viewBox="0 -4 8 8" refX="8" refY="0" markerWidth="7" markerHeight="7" orient="auto-start-reverse"><path d="M0,-4L8,0L0,4Z" fill="#536477"/></marker><marker id="arrow-MEM" viewBox="0 -4 8 8" refX="8" refY="0" markerWidth="7" markerHeight="7" orient="auto-start-reverse"><path d="M0,-4L8,0L0,4Z" fill="#2867b2"/></marker><marker id="arrow-ASSOC" viewBox="0 -4 8 8" refX="8" refY="0" markerWidth="7" markerHeight="7" orient="auto-start-reverse"><path d="M0,-4L8,0L0,4Z" fill="#9396a3"/></marker><marker id="arrow-PARSER" viewBox="0 -4 8 8" refX="8" refY="0" markerWidth="7" markerHeight="7" orient="auto-start-reverse"><path d="M0,-4L8,0L0,4Z" fill="#7956a5"/></marker></defs><rect width="100%" height="100%" fill="rgb(250, 251, 252)"/><g><g class="regions" style="opacity: 1;"/><rect class="peep-area" rx="36" style="opacity: 0;"/><g class="edges"><path class="edge CTRL" id="e5i0" d="M84,118 L84,138 L166,138 L166,166" stroke="#b63838" marker-start="url(#arrow-CTRL)" style="opacity: 1;"><title>#5[0] → #2 · CTRL</title></path><path class="edge ASSOC" id="e6i0" d="M387,46 C387,70 318,145 318,169" stroke="#9396a3" marker-start="url(#arrow-ASSOC)" style="opacity: 1;"><title>#6[0] → #1 · ASSOC</title></path><path class="edge MEM" id="e7i1" d="M204,118 L204,128 L95,128 L95,232 L143,232 L143,270" stroke="#2867b2" marker-start="url(#arrow-MEM)" style="opacity: 1;"><title>#7[1] → #3 · MEM</title></path><path class="edge DATA" id="e7i2" d="M166,222 L166,242 L167,242 L167,270" stroke="#536477" marker-start="url(#arrow-DATA)" style="opacity: 1;"><title>#7[2] → #5 · DATA</title></path><path class="edge DATA" id="e7i3" d="M318,222 L318,232 L191,232 L191,270" stroke="#536477" marker-start="url(#arrow-DATA)" style="opacity: 1;"><title>#7[3] → #6 · DATA</title></path><path class="edge MEM" id="e8i1" d="M155,326 L155,336 L201,336 L201,374" stroke="#2867b2" marker-start="url(#arrow-MEM)" style="opacity: 1;"><title>#8[1] → #7 · MEM</title></path><path class="edge DATA" id="e8i2" d="M166,222 L166,242 L225,242 L225,374" stroke="#536477" marker-start="url(#arrow-DATA)" style="opacity: 1;"><title>#8[2] → #5 · DATA</title></path><path class="edge DATA" id="e8i3" d="M324,118 L324,128 L388,128 L388,336 L249,336 L249,374" stroke="#536477" marker-start="url(#arrow-DATA)" style="opacity: 1;"><title>#8[3] → #4 · DATA</title></path><path class="edge CTRL" id="e10i0" d="M84,118 L84,478" stroke="#b63838" marker-start="url(#arrow-CTRL)" style="opacity: 1;"><title>#10[0] → #2 · CTRL</title></path><path class="edge MEM" id="e10i1" d="M213,430 L213,440 L114,440 L114,478" stroke="#2867b2" marker-start="url(#arrow-MEM)" style="opacity: 1;"><title>#10[1] → #8 · MEM</title></path><path class="edge DATA" id="e10i2" d="M324,118 L324,128 L388,128 L388,450 L144,450 L144,478" stroke="#536477" marker-start="url(#arrow-DATA)" style="opacity: 1;"><title>#10[2] → #4 · DATA</title></path></g><g class="edge-hits"/><g class="parser" style="opacity: 1;"/><g class="nodes"><g class="node" id="n1" data-id="1" transform="translate(24,24)" style="opacity: 1;"><path class="box" d="M0,0H360V44H0Z" fill="#fff1c4"/><text class="label" text-anchor="middle" x="180" y="18"><tspan>Start</tspan><tspan class="node-id">  #1</tspan></text><text class="type" text-anchor="middle" y="35" x="180"/><title>#1 Start
+Type not computed
+
+</title></g><g class="node" id="n2" data-id="2" transform="translate(24,68)" style="opacity: 1;"><path class="box" d="M0,0H120V44H0Z" fill="#fff1c4"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>$ctrl</tspan><tspan class="node-id">  #2/0</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#2 $ctrl
+Projection 0 of #1
+Type not computed
+
+[0] → #1  CTRL</title></g><g class="node" id="n3" data-id="3" transform="translate(144,68)" style="opacity: 1;"><path class="box" d="M0,0H120V44H0Z" fill="#dcecff"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>$mem</tspan><tspan class="node-id">  #3/1</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#3 $mem
+Projection 1 of #1
+Type not computed
+
+[0] → #1  MEM</title></g><g class="node" id="n4" data-id="4" transform="translate(264,68)" style="opacity: 1;"><path class="box" d="M0,0H120V44H0Z" fill="#edf3f7"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>arg</tspan><tspan class="node-id">  #4/2</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#4 arg
+Projection 2 of #1
+Type not computed
+
+[0] → #1  DATA</title></g><g class="node" id="n5" data-id="5" transform="translate(106,172)" style="opacity: 1;"><path class="box" d="M14,0H106Q120,0 120,14V30Q120,44 106,44H14Q0,44 0,30V14Q0,0 14,0Z" fill="#edf3f7"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>new Box</tspan><tspan class="node-id">  #5</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#5 new Box
+Type not computed
+
+[0] → #2  CTRL</title><circle class="port" cx="60" cy="-3" r="3" fill="#536477"/><text class="slot" x="60" y="-10" text-anchor="middle">0</text></g><g class="node" id="n6" data-id="6" transform="translate(258,172)" style="opacity: 1;"><path class="box" d="M14,0H106Q120,0 120,14V30Q120,44 106,44H14Q0,44 0,30V14Q0,0 14,0Z" fill="#edf3f7"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>#0</tspan><tspan class="node-id">  #6</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#6 #0
+Type not computed
+
+[0] → #1  ASSOC</title><circle class="port" cx="60" cy="-3" r="3" fill="#536477"/><text class="slot" x="60" y="-10" text-anchor="middle">0</text></g><g class="node" id="n7" data-id="7" transform="translate(95,276)" style="opacity: 1;"><path class="box" d="M10,0H110L120,10V34L110,44H10L0,34V10Z" fill="#dcecff"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>Store p.x</tspan><tspan class="node-id">  #7</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#7 Store p.x
+Type not computed
+
+[0] → —  CTRL
+[1] → #3  MEM
+[2] → #5  DATA
+[3] → #6  DATA</title><circle class="port" cx="24" cy="-3" r="3" fill="white"/><circle class="port" cx="48" cy="-3" r="3" fill="#536477"/><circle class="port" cx="72" cy="-3" r="3" fill="#536477"/><circle class="port" cx="96" cy="-3" r="3" fill="#536477"/><text class="slot" x="24" y="-10" text-anchor="middle">0</text><text class="slot" x="48" y="-10" text-anchor="middle">1</text><text class="slot" x="72" y="-10" text-anchor="middle">2</text><text class="slot" x="96" y="-10" text-anchor="middle">3</text></g><g class="node" id="n8" data-id="8" transform="translate(153,380)" style="opacity: 1;"><path class="box" d="M10,0H110L120,10V34L110,44H10L0,34V10Z" fill="#dcecff"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>Store p.x</tspan><tspan class="node-id">  #8</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#8 Store p.x
+Type not computed
+
+[0] → —  CTRL
+[1] → #7  MEM
+[2] → #5  DATA
+[3] → #4  DATA</title><circle class="port" cx="24" cy="-3" r="3" fill="white"/><circle class="port" cx="48" cy="-3" r="3" fill="#536477"/><circle class="port" cx="72" cy="-3" r="3" fill="#536477"/><circle class="port" cx="96" cy="-3" r="3" fill="#536477"/><text class="slot" x="24" y="-10" text-anchor="middle">0</text><text class="slot" x="48" y="-10" text-anchor="middle">1</text><text class="slot" x="72" y="-10" text-anchor="middle">2</text><text class="slot" x="96" y="-10" text-anchor="middle">3</text></g><g class="node" id="n10" data-id="10" transform="translate(54,484)" style="opacity: 1;"><path class="box" d="M0,0H120V44H0Z" fill="#fff1c4"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>Return</tspan><tspan class="node-id">  #10</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#10 Return
+Type not computed
+
+[0] → #2  CTRL
+[1] → #8  MEM
+[2] → #4  DATA</title><circle class="port" cx="30" cy="-3" r="3" fill="#536477"/><circle class="port" cx="60" cy="-3" r="3" fill="#536477"/><circle class="port" cx="90" cy="-3" r="3" fill="#536477"/><text class="slot" x="30" y="-10" text-anchor="middle">0</text><text class="slot" x="60" y="-10" text-anchor="middle">1</text><text class="slot" x="90" y="-10" text-anchor="middle">2</text></g></g><g class="region-heads" style="opacity: 1;"/><g class="shortcuts" style="opacity: 1;"/><g class="peep-ghosts" pointer-events="none"/></g></svg>
diff --git a/chapter10a/docs/load-after-store-before.json b/chapter10a/docs/load-after-store-before.json
new file mode 100644
index 00000000..5a15a4e4
--- /dev/null
+++ b/chapter10a/docs/load-after-store-before.json
@@ -0,0 +1,21 @@
+{
+  "ver": 1,
+  "comp": "load-after-store-before",
+  "step": 1,
+  "roots": [10],
+  "scope": 0,
+  "nodes": [
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+    {"id": 2, "label": "$ctrl", "type": null, "kind": "CTRL", "edges": [{"idx": 0, "def": 1, "role": "CTRL", "label": null}], "proj": {"par": 1, "idx": 0}},
+    {"id": 3, "label": "$mem", "type": null, "kind": "MEM", "edges": [{"idx": 0, "def": 1, "role": "MEM", "label": null}], "proj": {"par": 1, "idx": 1}},
+    {"id": 4, "label": "arg", "type": null, "kind": "DATA", "edges": [{"idx": 0, "def": 1, "role": "DATA", "label": null}], "proj": {"par": 1, "idx": 2}},
+    {"id": 5, "label": "new Box", "type": null, "kind": "DATA", "edges": [{"idx": 0, "def": 2, "role": "CTRL", "label": null}], "proj": null},
+    {"id": 6, "label": "#0", "type": null, "kind": "DATA", "edges": [{"idx": 0, "def": 1, "role": "ASSOC", "label": null}], "proj": null},
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+    {"id": 8, "label": "Store p.x", "type": null, "kind": "MEM", "edges": [{"idx": 0, "def": 0, "role": "CTRL", "label": null}, {"idx": 1, "def": 7, "role": "MEM", "label": null}, {"idx": 2, "def": 5, "role": "DATA", "label": null}, {"idx": 3, "def": 4, "role": "DATA", "label": null}], "proj": null},
+    {"id": 9, "label": "Load p.x", "type": null, "kind": "DATA", "edges": [{"idx": 0, "def": 0, "role": "CTRL", "label": null}, {"idx": 1, "def": 8, "role": "MEM", "label": null}, {"idx": 2, "def": 5, "role": "DATA", "label": null}, {"idx": 3, "def": 0, "role": "DATA", "label": null}], "proj": null},
+    {"id": 10, "label": "Return", "type": null, "kind": "CTRL", "edges": [{"idx": 0, "def": 2, "role": "CTRL", "label": null}, {"idx": 1, "def": 8, "role": "MEM", "label": null}, {"idx": 2, "def": 9, "role": "DATA", "label": null}], "proj": null}
+  ],
+  "groups": [
+  ]
+}
diff --git a/chapter10a/docs/load-after-store-before.svg b/chapter10a/docs/load-after-store-before.svg
new file mode 100644
index 00000000..cdb152e3
--- /dev/null
+++ b/chapter10a/docs/load-after-store-before.svg
@@ -0,0 +1,107 @@
+<svg aria-label="Compiler graph" width="471" height="662" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 471 662" style="font-family: sans-serif;"><style>
+    html, body { height:100%; margin:0; font-family:sans-serif; }
+    .viewer { height:100%; display:grid; grid-template-rows:auto minmax(0,1fr) auto; }
+    .source { padding:8px; border-bottom:1px solid #ccc; }
+    #program { width:min(600px,80vw); vertical-align:middle; }
+    #status { margin-top:4px; }
+    #graph { min-height:0; overflow:hidden; position:relative; background:#fafbfc; }
+    #elk { width:100%; height:100%; }
+    #graph svg { display:block; }
+    .tools { display:flex; flex-wrap:wrap; align-items:center; gap:14px; margin-top:8px; font-size:12px; }
+    .hint { color:#616c78; }
+    .ctrl { color:#b63838; } .mem { color:#2867b2; } .data { color:#536477; }
+    .edge { fill:none; stroke-width:1.5; }
+    .edge.CTRL { stroke-width:2; }
+    .edge.ASSOC { stroke-dasharray:4 4; }
+    .edge.PARSER { stroke-dasharray:5 4; }
+    .parser rect { fill:#f6f0ff; stroke:#7956a5; stroke-width:1.5; stroke-dasharray:5 4; }
+    .edge.selected { stroke-width:3.5; }
+    .edge.bundle { stroke-width:4; }
+    .edge.bundle.selected { stroke-width:6; }
+    .edge-hit { fill:none; stroke:transparent; stroke-width:12; vector-effect:non-scaling-stroke; pointer-events:stroke; cursor:pointer; }
+    .edge-jump { fill:transparent; pointer-events:all; cursor:pointer; }
+    .node { cursor:pointer; }
+    .box { stroke:#758191; stroke-width:1; }
+    .node.held .box { stroke-dasharray:5 3; }
+    .node.near .box { stroke:#c18221; stroke-width:2; }
+    .node.focus .box { stroke:#9c4900; stroke-width:3; }
+    .node.selected .box { stroke:#1569b9; stroke-width:3; }
+    .node.folded .box { stroke-width:4; }
+    .node.folding .box { fill:#f4ccd7; }
+    .fold-tag { font-size:9px; font-weight:700; fill:#963751; }
+    .peep-area { fill:#fff3d9; fill-opacity:.8; stroke:#c18221; stroke-width:2; pointer-events:none; }
+    .node.peep-edit .box { stroke:#9c4900; stroke-width:3; }
+    .node.error .box { stroke:#b42318; stroke-width:4; }
+    #event.error { color:#b42318; font-weight:600; white-space:pre-wrap; overflow-wrap:anywhere; }
+    .peep-ghosts { pointer-events:none; }
+    .region-box { stroke:#9da9b8; stroke-width:1.5; }
+    .fold-btn { cursor:pointer; }
+    .fold-btn rect { fill:white; stroke:#596674; }
+    .fold-btn text { font-size:14px; fill:#152330; }
+    .fold-btn:focus rect { stroke:#1569b9; stroke-width:2; }
+    .shortcut { cursor:pointer; }
+    .shortcut path { fill:none; stroke-width:1.5; }
+    .shortcut rect { fill:#fff8ec; stroke:#b63838; stroke-dasharray:3 2; }
+    .shortcut text { font-size:11px; fill:#783030; }
+    .shortcut.selected rect, .shortcut:focus rect { stroke-width:2.5; }
+    .label { font-size:12px; fill:#152330; font-weight:600; }
+    .node-id { font-size:10px; fill:#596674; font-weight:400; }
+    .type { font-size:11px; fill:#455768; }
+    .port { stroke:#536477; stroke-width:1; }
+    .row { stroke:#b6afcf; stroke-width:1; }
+    .bind { font-size:12px; fill:#152330; }
+    .slot { font-size:10px; fill:#364352; paint-order:stroke; stroke:#fafbfc; stroke-width:3; }
+    #detail { position:absolute; top:8px; right:8px; margin:0; padding:12px; max-width:320px;
+      max-height:45%; overflow:auto; white-space:pre-wrap; overflow-wrap:anywhere;
+      background:#fffffff2; border:1px solid #bac5d0; border-radius:4px; font-size:12px; }
+    .controls { display:flex; flex-wrap:wrap; justify-content:center; align-items:center; gap:6px; padding:6px; }
+    .button { color:white; background:black; font-size:20px; min-width:30px; }
+    .button:disabled { background:grey; }
+    .count { font-size:20px; min-width:35px; text-align:center; }
+    #N { width:6ch; }
+    #scrub { width:clamp(120px,35vw,600px); }
+  </style><defs><marker id="arrow-CTRL" viewBox="0 -4 8 8" refX="8" refY="0" markerWidth="7" markerHeight="7" orient="auto-start-reverse"><path d="M0,-4L8,0L0,4Z" fill="#b63838"/></marker><marker id="arrow-DATA" viewBox="0 -4 8 8" refX="8" refY="0" markerWidth="7" markerHeight="7" orient="auto-start-reverse"><path d="M0,-4L8,0L0,4Z" fill="#536477"/></marker><marker id="arrow-MEM" viewBox="0 -4 8 8" refX="8" refY="0" markerWidth="7" markerHeight="7" orient="auto-start-reverse"><path d="M0,-4L8,0L0,4Z" fill="#2867b2"/></marker><marker id="arrow-ASSOC" viewBox="0 -4 8 8" refX="8" refY="0" markerWidth="7" markerHeight="7" orient="auto-start-reverse"><path d="M0,-4L8,0L0,4Z" fill="#9396a3"/></marker><marker id="arrow-PARSER" viewBox="0 -4 8 8" refX="8" refY="0" markerWidth="7" markerHeight="7" orient="auto-start-reverse"><path d="M0,-4L8,0L0,4Z" fill="#7956a5"/></marker></defs><rect width="100%" height="100%" fill="rgb(250, 251, 252)"/><g><g class="regions" style="opacity: 1;"/><rect class="peep-area" rx="36" style="opacity: 0;"/><g class="edges"><path class="edge CTRL" id="e5i0" d="M84,118 L84,138 L318,138 L318,166" stroke="#b63838" marker-start="url(#arrow-CTRL)" style="opacity: 1;"><title>#5[0] → #2 · CTRL</title></path><path class="edge ASSOC" id="e6i0" d="M387,46 C387,70 166,145 166,169" stroke="#9396a3" marker-start="url(#arrow-ASSOC)" style="opacity: 1;"><title>#6[0] → #1 · ASSOC</title></path><path class="edge MEM" id="e7i1" d="M204,118 L204,128 L95,128 L95,232 L143,232 L143,270" stroke="#2867b2" marker-start="url(#arrow-MEM)" style="opacity: 1;"><title>#7[1] → #3 · MEM</title></path><path class="edge DATA" id="e7i2" d="M318,222 L318,242 L167,242 L167,270" stroke="#536477" marker-start="url(#arrow-DATA)" style="opacity: 1;"><title>#7[2] → #5 · DATA</title></path><path class="edge DATA" id="e7i3" d="M166,222 L166,232 L191,232 L191,270" stroke="#536477" marker-start="url(#arrow-DATA)" style="opacity: 1;"><title>#7[3] → #6 · DATA</title></path><path class="edge MEM" id="e8i1" d="M155,326 L155,336 L294,336 L294,374" stroke="#2867b2" marker-start="url(#arrow-MEM)" style="opacity: 1;"><title>#8[1] → #7 · MEM</title></path><path class="edge DATA" id="e8i2" d="M318,222 L318,374" stroke="#536477" marker-start="url(#arrow-DATA)" style="opacity: 1;"><title>#8[2] → #5 · DATA</title></path><path class="edge DATA" id="e8i3" d="M324,118 L324,128 L388,128 L388,232 L342,232 L342,374" stroke="#536477" marker-start="url(#arrow-DATA)" style="opacity: 1;"><title>#8[3] → #4 · DATA</title></path><path class="edge MEM" id="e9i1" d="M306,430 L306,440 L375,440 L375,478" stroke="#2867b2" marker-start="url(#arrow-MEM)" style="opacity: 1;"><title>#9[1] → #8 · MEM</title></path><path class="edge DATA" id="e9i2" d="M318,222 L318,242 L399,242 L399,478" stroke="#536477" marker-start="url(#arrow-DATA)" style="opacity: 1;"><title>#9[2] → #5 · DATA</title></path><path class="edge CTRL" id="e10i0" d="M84,118 L84,582" stroke="#b63838" marker-start="url(#arrow-CTRL)" style="opacity: 1;"><title>#10[0] → #2 · CTRL</title></path><path class="edge MEM" id="e10i1" d="M306,430 L306,440 L114,440 L114,582" stroke="#2867b2" marker-start="url(#arrow-MEM)" style="opacity: 1;"><title>#10[1] → #8 · MEM</title></path><path class="edge DATA" id="e10i2" d="M387,534 L387,544 L144,544 L144,582" stroke="#536477" marker-start="url(#arrow-DATA)" style="opacity: 1;"><title>#10[2] → #9 · DATA</title></path></g><g class="edge-hits"/><g class="parser" style="opacity: 1;"/><g class="nodes"><g class="node" id="n1" data-id="1" transform="translate(24,24)" style="opacity: 1;"><path class="box" d="M0,0H360V44H0Z" fill="#fff1c4"/><text class="label" text-anchor="middle" x="180" y="18"><tspan>Start</tspan><tspan class="node-id">  #1</tspan></text><text class="type" text-anchor="middle" y="35" x="180"/><title>#1 Start
+Type not computed
+
+</title></g><g class="node" id="n2" data-id="2" transform="translate(24,68)" style="opacity: 1;"><path class="box" d="M0,0H120V44H0Z" fill="#fff1c4"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>$ctrl</tspan><tspan class="node-id">  #2/0</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#2 $ctrl
+Projection 0 of #1
+Type not computed
+
+[0] → #1  CTRL</title></g><g class="node" id="n3" data-id="3" transform="translate(144,68)" style="opacity: 1;"><path class="box" d="M0,0H120V44H0Z" fill="#dcecff"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>$mem</tspan><tspan class="node-id">  #3/1</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#3 $mem
+Projection 1 of #1
+Type not computed
+
+[0] → #1  MEM</title></g><g class="node" id="n4" data-id="4" transform="translate(264,68)" style="opacity: 1;"><path class="box" d="M0,0H120V44H0Z" fill="#edf3f7"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>arg</tspan><tspan class="node-id">  #4/2</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#4 arg
+Projection 2 of #1
+Type not computed
+
+[0] → #1  DATA</title></g><g class="node" id="n5" data-id="5" transform="translate(258,172)" style="opacity: 1;"><path class="box" d="M14,0H106Q120,0 120,14V30Q120,44 106,44H14Q0,44 0,30V14Q0,0 14,0Z" fill="#edf3f7"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>new Box</tspan><tspan class="node-id">  #5</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#5 new Box
+Type not computed
+
+[0] → #2  CTRL</title><circle class="port" cx="60" cy="-3" r="3" fill="#536477"/><text class="slot" x="60" y="-10" text-anchor="middle">0</text></g><g class="node" id="n6" data-id="6" transform="translate(106,172)" style="opacity: 1;"><path class="box" d="M14,0H106Q120,0 120,14V30Q120,44 106,44H14Q0,44 0,30V14Q0,0 14,0Z" fill="#edf3f7"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>#0</tspan><tspan class="node-id">  #6</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#6 #0
+Type not computed
+
+[0] → #1  ASSOC</title><circle class="port" cx="60" cy="-3" r="3" fill="#536477"/><text class="slot" x="60" y="-10" text-anchor="middle">0</text></g><g class="node" id="n7" data-id="7" transform="translate(95,276)" style="opacity: 1;"><path class="box" d="M10,0H110L120,10V34L110,44H10L0,34V10Z" fill="#dcecff"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>Store p.x</tspan><tspan class="node-id">  #7</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#7 Store p.x
+Type not computed
+
+[0] → —  CTRL
+[1] → #3  MEM
+[2] → #5  DATA
+[3] → #6  DATA</title><circle class="port" cx="24" cy="-3" r="3" fill="white"/><circle class="port" cx="48" cy="-3" r="3" fill="#536477"/><circle class="port" cx="72" cy="-3" r="3" fill="#536477"/><circle class="port" cx="96" cy="-3" r="3" fill="#536477"/><text class="slot" x="24" y="-10" text-anchor="middle">0</text><text class="slot" x="48" y="-10" text-anchor="middle">1</text><text class="slot" x="72" y="-10" text-anchor="middle">2</text><text class="slot" x="96" y="-10" text-anchor="middle">3</text></g><g class="node" id="n8" data-id="8" transform="translate(246,380)" style="opacity: 1;"><path class="box" d="M10,0H110L120,10V34L110,44H10L0,34V10Z" fill="#dcecff"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>Store p.x</tspan><tspan class="node-id">  #8</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#8 Store p.x
+Type not computed
+
+[0] → —  CTRL
+[1] → #7  MEM
+[2] → #5  DATA
+[3] → #4  DATA</title><circle class="port" cx="24" cy="-3" r="3" fill="white"/><circle class="port" cx="48" cy="-3" r="3" fill="#536477"/><circle class="port" cx="72" cy="-3" r="3" fill="#536477"/><circle class="port" cx="96" cy="-3" r="3" fill="#536477"/><text class="slot" x="24" y="-10" text-anchor="middle">0</text><text class="slot" x="48" y="-10" text-anchor="middle">1</text><text class="slot" x="72" y="-10" text-anchor="middle">2</text><text class="slot" x="96" y="-10" text-anchor="middle">3</text></g><g class="node" id="n9" data-id="9" transform="translate(327,484)" style="opacity: 1;"><path class="box" d="M14,0H106Q120,0 120,14V30Q120,44 106,44H14Q0,44 0,30V14Q0,0 14,0Z" fill="#edf3f7"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>Load p.x</tspan><tspan class="node-id">  #9</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#9 Load p.x
+Type not computed
+
+[0] → —  CTRL
+[1] → #8  MEM
+[2] → #5  DATA
+[3] → —  DATA</title><circle class="port" cx="24" cy="-3" r="3" fill="white"/><circle class="port" cx="48" cy="-3" r="3" fill="#536477"/><circle class="port" cx="72" cy="-3" r="3" fill="#536477"/><circle class="port" cx="96" cy="-3" r="3" fill="white"/><text class="slot" x="24" y="-10" text-anchor="middle">0</text><text class="slot" x="48" y="-10" text-anchor="middle">1</text><text class="slot" x="72" y="-10" text-anchor="middle">2</text><text class="slot" x="96" y="-10" text-anchor="middle">3</text></g><g class="node" id="n10" data-id="10" transform="translate(54,588)" style="opacity: 1;"><path class="box" d="M0,0H120V44H0Z" fill="#fff1c4"/><text class="label" text-anchor="middle" x="60" y="18"><tspan>Return</tspan><tspan class="node-id">  #10</tspan></text><text class="type" text-anchor="middle" y="35" x="60"/><title>#10 Return
+Type not computed
+
+[0] → #2  CTRL
+[1] → #8  MEM
+[2] → #9  DATA</title><circle class="port" cx="30" cy="-3" r="3" fill="#536477"/><circle class="port" cx="60" cy="-3" r="3" fill="#536477"/><circle class="port" cx="90" cy="-3" r="3" fill="#536477"/><text class="slot" x="30" y="-10" text-anchor="middle">0</text><text class="slot" x="60" y="-10" text-anchor="middle">1</text><text class="slot" x="90" y="-10" text-anchor="middle">2</text></g></g><g class="region-heads" style="opacity: 1;"/><g class="shortcuts" style="opacity: 1;"/><g class="peep-ghosts" pointer-events="none"/></g></svg>
diff --git a/graph/README.md b/graph/README.md
index 7479aaf9..f0e32d9d 100644
--- a/graph/README.md
+++ b/graph/README.md
@@ -143,6 +143,19 @@ The chapter `docs/Makefile` rules select JSON before a same-named legacy DOT
 file. They accept `PYTHON` and `DOC_BROWSER` overrides, for example
 `make -C chapter01/docs PYTHON=python DOC_BROWSER=msedge` from the repository root.
 
+For a before/after comparison, keep node IDs stable across the two snapshots
+and place their SVGs in a two-column Markdown table:
+
+```markdown
+| Before | After |
+|---|---|
+| ![Before the rewrite](docs/before.svg) | ![After the rewrite](docs/after.svg) |
+```
+
+This keeps both graphs side by side in the chapter README. Chapter 10a's
+[load-after-store example](../chapter10a/README.md#local-memory-optimizations)
+uses this format to isolate a single rewrite.
+
 The compact memory-dependency schematics in 10b retain `.gv` sources to
 preserve their deliberate horizontal layouts. They use the viewer palette and
 node shapes; definitions are left of uses horizontally and above uses vertically,