1 LLVM IR

Consider the following function compiled into LLVM IR (or download [foo.ll])

target triple = "x86_64-pc-linux-gnu"

define i64 @foo(i32 %x) {
entry:
  %x.addr = alloca i32
  %res = alloca i64
  store i32 %x, ptr %x.addr
  store i64 0, ptr %res
  br label %while.cond

while.cond:
  %0 = load i32, ptr %x.addr
  %cmp = icmp sgt i32 %0, 0
  br i1 %cmp, label %while.body, label %while.end

while.body:
  %1 = load i64, ptr %res
  %mul = mul i64 %1, 10
  %add = add i64 %mul, 3
  store i64 %add, ptr %res
  %2 = load i32, ptr %x.addr
  %dec = add i32 %2, -1
  store i32 %dec, ptr %x.addr
  br label %while.cond

while.end:
  %3 = load i64, ptr %res
  ret i64 %3
}

1. Describe (in a sentence or two) what this function does.

2. Rewrite the foo function from the previous page so that it does not use any memory allocation, load, or store operations.

   (Hint: you have to use phi instructions.)

2 Goto harmful

Write a C program with ``spaghetti code’’ that fits the following requirements:

• It uses goto statements and labels
• It is relatively short (say, 30ish lines of code)
• It does something mildly useful or interesting
• It is hard to understand because of the goto statements

1. Copy your C spaghetti code program below.

2. Say what it is that your program actually does.

   (Make sure part (b) is on a different page or side than part (a).)