# In-Class Exercise 8: SSA Destruction

Consider the following pseudo-SSA.

    fn(%0, %1) {
    b1:
      %2 = add %0, %1
      br %b2

    b2:
      %3 = phi [%b1: %1], [%b3: %4]
      %4 = phi [%b1: %0], [%b3: %3]
      %5 = phi [%b1: %2], [%b3: %3]
      %6 = phi [%b1: 0], [%b3: %8]
      %7 = icmp lt %3, %6
      br %7, %b3, %b4

    b3:
      %8 = add %6, 1
      %9 = icmp gt %8, %1
      br %9, %b4, %b2

    b4:
      %10 = phi [%b2: %4], [%b3, %3]
      %11 = phi [%b2: %5], [%b3, %8]
      %12 = add %10, %11
      ret %12
    }

1. Are there dependencies between phi nodes? If so, which?
2. Does the CFG contain critical edges?
3. Destruct SSA and transform the code into a form where you have unlimited registers. This means that you can assign values multiple times.
    3.1. Do by breaking critical edges.
    3.2. Do by copying used values.

## Solution

```
base64 -d <<EOF | gunzip
H4sIAAAAAAAAA71Sy07DMBC8+yv2YgmkHuJH0rSo3xLFtVNVlLRyTBFC/Du7mzihQkjAgVwyWs/O
jnfc9c0+HlMT/CEMjYvnx9DfyWIFUt3Dm3BqKwCkhh203sN4QBWDlRFZQgWhkpAmVCGikosgnRbC
aZZZY/m4f7rAKaECSlUTZ43YUcFpZ5FumF7nqdUKeNQm9x+wv56sUP+G+50dfzTQsoKajSt2TvwY
Eh2QqcwqyLhlqAiW2boVpPqJZBZSfUMaL1jOnDQjM4vzplLezyKgxbsQosMkzpfX5tqensPwvxl8
v4Ilmd/mIhMLGbj5HoAuyZP7EHzw0HYpxJc2+uFPG5ysJ/U1GX4V/CZ+9iIwhQ+8bK17DwMAAA==
EOF
```