Update homework 1 and 2

README.md

@@ -34,7 +34,7 @@ cargo test --release   # release build test
 cargo test <test-name> # run a particular test
 ```
 
-`<test-name>` can be `test_ast_print`, `ir_smoke`, ...
+`<test-name>` can be `test_examples_write_c`, `test_examples_irgen`, ...
 
 
 ## Fuzzing
@@ -44,10 +44,7 @@ cargo test <test-name> # run a particular test
 ```sh
 # Ubuntu 18.04 or higher
 apt install -y make cmake python3
-
-# MacOS
-xcode-select install
-brew install cmake python3
+apt install -y csmith libcsmith-dev creduce
 ```
 
 ### Run
@@ -59,5 +56,28 @@ python3 tests/fuzz.py --help        # print options
 python3 tests/fuzz.py --print -n10  # test C AST printer for 10 times
 ```
 
-We use [Csmith](https://embed.cs.utah.edu/csmith/) to randomly generate C source codes.  Csmith will
-be automatically downloaded and built by the test script.
+We use `csmith` to randomly generate C source codes. `csmith` will be automatically downloaded and
+built by the test script. For more information, we refer to the
+[Csmith](https://embed.cs.utah.edu/csmith/) homepage.
+
+### Reduce
+
+When the fuzzer finds a buggy input program for your compiler, it is highly likely that the input
+program is too big to manually inspect.  We use `creduce` that reduces the buggy input program as
+much as possible.
+
+Suppose `tests/test_polished.c` is the buggy input program. Then the following script reduces the
+program to `tests/test_reduced.c`:
+
+```sh
+python3 tests/fuzz.py --reduce <fuzz-option>
+```
+
+`<fuzz-option>` can be `--print` or `--irgen`. It shall be the one used in [Run](#run).
+
+### How it reduces test case?
+
+The script performs unguided test-case reduction using `creduce`: given a buggy program, it randomly
+reduces the program; check if the reduced program still fails on the test, and if so, replaces the
+given program with the reduced one; repeat until you get a small enough buggy program. For more
+information, we refer to the [Creduce](https://embed.cs.utah.edu/creduce/) homepage.