sysy-smith

A fork of Csmith that generates random programs valid under the SysY language — a simplified C subset used in the PKU compiler course.

Changes from Csmith

Restricted language features

Feature	Original Csmith	sysy-smith
Types	int, char, short, long, unsigned, …	int only
Integer literals	Any suffix (UL, LL, …), any range	No suffix, clamped to [0, 2147483647]
Operators	Bitwise (&, |, ^, ~), shift (<<, >>)	Removed
Compound assignment	+=, -=, *=, /=, %=, <<=, >>=, &=, |=, ^=	Removed
Increment/decrement	++, -- (pre and post)	Removed
Type casts	Present	Removed
for loops	Present	Removed (SysY only has while)
struct / union	Present	Removed
Pointers	Present	Removed
Arrays	Present	Removed
static / volatile / const	Present	Removed
Comma operator	Present	Removed
Assignment as expression	Present	Removed
#include / #define / macros	Present in output	Removed from output
Checksum / hash infrastructure	Present	Removed

Output format

• No #include or #define directives in generated files.
• main() takes no arguments and returns 0 unconditionally.
• Empty parameter lists use () instead of (void).

Function ordering (--no-forward-decls / --forward-decls)

By default (--no-forward-decls), sysy-smith topologically sorts functions so every callee is defined before its callers — no forward declarations are needed. This is required because SysY does not support function declarations.

Pass --forward-decls to restore the original Csmith behaviour (forward declarations emitted, functions in creation order).

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About Csmith

Csmith is a random generator of C programs. It's primary purpose is to find compiler bugs with random programs, using differential testing as the test oracle.

Csmith can be used outside of the field of compiler testing. If your application needs a test suite of C programs and you don't bother to write them, feel free to give Csmith a try.

Csmith outputs C programs free of undefined behaviors (believe us, that's not trivial), and the statistics of each generated program.

Install sysy-smith

Pre-built binaries for x86_64 and aarch64 Linux are available on the Releases page.

To build from source (Ubuntu):

git clone https://github.com/hsqStephenZhang/sysy-smith.git
cd sysy-smith
sudo apt install g++ cmake m4
cmake -S . -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build --target sysy-smith -j$(nproc)
# binary at build/src/sysy-smith

Use sysy-smith

Generate a random SysY-compatible program and compile it with a SysY compiler:

./sysy-smith --no-argc --seed 42 > test.c
kira -koopa test.c -o test.koopa

Key options:

• --no-argc — omit argc/argv from main (required for SysY)
• --seed <N> — set the random seed for reproducible output
• --no-forward-decls — (default) emit functions in dependency order, no forward declarations
• --forward-decls — emit forward declarations and functions in creation order

Use ./sysy-smith -h or ./sysy-smith -hh to see all available options.

Here is a slightly outdated but still relevant document about using Csmith for compiler testing.

History

Csmith was originally developed at the University of Utah by:

• Xuejun Yang
• Yang Chen
• Eric Eide
• John Regehr

as part of a research project on compiler testing. The research is best summarized by our paper Finding and Understanding Bugs in C Compilers. More research info can be found here.

Csmith was open sourced in 2009. We try to keep maintaining it as an open source project using our discretionary time. As much, the response to bug reports or feature requests might be delayed.

Community

Please use github issues to report bugs or suggestions.

We have a mailing list for discussing Csmith. Please visit here to subscribe.