add L8.pdf and complement in 11.06

notes/8.md

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+# Dataflow Analysis
+
+Optimization means improving resource utilization not changing what the program computes.
+Resource utilization means many things:
+* **Execution time**
+* Code size
+* Network messages sent.
+
+## Basic Block (BB)
+
+A BB is a maximum sequence of instructions with **no labels**, **no jumps**
+All instructions in a BB has fixed control flow.
+
+## Control Flow Graph
+
+```mermaid
+flowchart TD
+    Entry --> A
+    A[BB1] --> B[BB2]
+    A --> C[BB3]
+    B --> D[BB4]
+    C --> D
+    D --> E[BB5]
+    E --> G[BB7]
+    E --> F[BB6]
+    G --> Exit
+    F --> Exit
+```
+
+## Local Optimization
+
+### Algebraic Simplification
+
+x := x + 0 -> x := 0
+y := y ** 2 -> y := y * y
+x := x * 8 -> x := x << 3
+x := x * 15 -> t := x << 4; x := t - x
+
+### Constant Folding
+
+x := 2 + 2 -> x := 4
+if 2 < 0 jump L -> nop
+if 2 > 0 jump L -> jump L
+
+But Constant folding can be dangerous on cross-compilation (in precision).
+
+
+### Unreachable Code
+
+### Dead Code Elimination
+
+## Global Optimization