C-Vise

About

C-Vise is a super-parallel Python port of the C-Reduce. The port is fully compatible to the C-Reduce and uses the same efficient LLVM-based C/C++ reduction tool named clang_delta.

C-Vise is a tool that takes a large C, C++ or OpenCL program that has a property of interest (such as triggering a compiler bug) and automatically produces a much smaller C/C++ or OpenCL program that has the same property. It is intended for use by people who discover and report bugs in compilers and other tools that process C/C++ or OpenCL code.

The project also contains a simple wrapper cvise-delta which simulates the same behavior as original delta tool (but in super-parallel way).

NOTE: C-Vise happens to do a pretty good job reducing the size of programs in languages other than C/C++, such as JavaScript and Rust. If you need to reduce programs in some other language, please give it a try.

NOTE: Binary pass group (--pass-group=binary) contains an experimental pass that can reduce GCC's .gcda files.

Speed Comparison

I made a comparison for couple of GCC bug reports on my AMD Ryzen 7 2700X Eight-Core Processor machine with the following results:

Test-case	Size	C-Vise Reduction	C-Reduce Reduction	Speed Up
PR92516	6.5 MB	35m	77m	220%
PR94523	2.1 MB	15m	33m	220%
PR94632	3.3 MB	20m	28m	40%
PR94937	8.5 MB	242m	303m	125%

Installation

See INSTALL.md.

Usage example

The C-Vise can be used for a reduction of a compiler crash. In this case, let's consider an existing PR94534:

Original test-case (pr94534.C file):

template<typename T>
class Demo
{
  struct
  {
    Demo* p;
  } payload{this};
  friend decltype(payload);
};

int main()
{
  Demo<int> d;
}

The program crashes in GCC, but is accepted with Clang:

$ g++ pr94534.C -c
pr94534.C: In instantiation of ‘class Demo<int>’:
pr94534.C:13:13:   required from here
pr94534.C:7:5: internal compiler error: Segmentation fault
    7 |   } payload{this};
      |     ^~~~~~~
0x10a1d8f crash_signal
	/home/marxin/Programming/gcc/gcc/toplev.c:328
0x7ffff78fef1f ???
	/usr/src/debug/glibc-2.31-4.1.x86_64/signal/../sysdeps/unix/sysv/linux/x86_64/sigaction.c:0
0xae31a8 instantiate_class_template_1
	/home/marxin/Programming/gcc/gcc/cp/pt.c:11973
...
$ clang++ pr94534.C -c

So let's build a reduction script so that it will grep for instantiate_class_template_1 on the standard error output and that it compiles with Clang:

reduce-ice.sh:

#!/bin/sh
g++ pr94534.C -c 2>&1 | grep 'instantiate_class_template_1' && clang++ -c pr94534.C

The reduction can be then run with:

$ cvise ./reduce-ice.sh pr94534.C
INFO ===< 30356 >===
INFO running 16 interestingness tests in parallel
INFO INITIAL PASSES
INFO ===< IncludesPass >===
...
template <typename> class a {
  int b;
  friend decltype(b);
};
void c() { a<int> d; }

Notes