Study LLVM IR: Compile C Code and Read the .ll Output

Your Task

Explore LLVM IR by compiling C code and analyzing the output. This is a research-oriented task.

Requirements

1. Generate LLVM IR:

   • Write a simple C program (provided or your own)
   • Compile with clang -S -emit-llvm
   • Compare output with and without optimizations (-O0 vs -O2)

2. Analyze the IR:

   • Identify basic blocks
   • Find SSA variable assignments
   • Locate phi-nodes at control flow merges
   • Understand type annotations

3. Answer questions:

   • How many basic blocks are in the function?
   • What optimization passes were applied?
   • How does LLVM represent loops?
   • Where are phi-nodes inserted?

4. Experiment:

   • Modify the C code and see how IR changes
   • Try different optimization levels (-O0, -O1, -O2, -O3)
   • Compare with gcc -S -fdump-tree-all output

Provided C Program

Use this program to start:

cCopy
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Success Criteria

• Successfully generate LLVM IR from C code
• Identify and explain key IR structures (SSA, phi-nodes, types)
• Compare unoptimized vs optimized IR
• Answer questions about IR structure