Alive2

Alive2 consists of several libraries and tools for analysis and verification of LLVM code and transformations.
This fork is modified to pre-convert the SWPP2022-specific intrinsics. See here for the original repo

WARNING

Alive2 does not support inter-procedural transformations. Alive2 may crash or produce spurious counterexamples if run with such passes.

Prerequisites

To build Alive2 you need recent versions of:

• cmake
• gcc/clang
• re2c
• Z3
• LLVM (With RTTI and exception handling enabled: the build script in class repo already does that)

Building

Use the build.sh to build alive-tv. Default LLVM_DIR and Z3_DIR should work for the default CI docker image.

Running the Standalone Translation Validation Tool (alive-tv)

This tool has two modes.

In the first mode, specify a source (original) and target (optimized) IR file. For example, let's prove that removing nsw is correct for addition:

$ ./alive-tv src.ll tgt.ll

----------------------------------------
define i32 @f(i32 %a, i32 %b) {
  %add = add nsw i32 %b, %a
  ret i32 %add
}
=>
define i32 @f(i32 %a, i32 %b) {
  %add = add i32 %b, %a
  ret i32 %add
}

Transformation seems to be correct!

Flipping the inputs yields a counterexample, since it's not correct, in general, to add nsw. If you are not interested in counterexamples using undef, you can use the command-line argument -disable-undef-input.

In the second mode, specify a single unoptimized IR file. alive-tv will optimize it using an optimization pipeline similar to -O2, but without any interprocedural passes, and then attempt to validate the translation.

For example, as of February 6 2020, the release/10.x branch contains an optimizer bug that can be triggered as follows:

$ cat foo.ll
define i3 @foo(i3) {
  %x1 = sub i3 0, %0
  %x2 = icmp ne i3 %0, 0
  %x3 = zext i1 %x2 to i3
  %x4 = lshr i3 %x1, %x3
  %x5 = lshr i3 %x4, %x3
  ret i3 %x5
}
$ ./alive-tv foo.ll

----------------------------------------
define i3 @foo(i3 %0) {
  %x1 = sub i3 0, %0
  %x2 = icmp ne i3 %0, 0
  %x3 = zext i1 %x2 to i3
  %x4 = lshr i3 %x1, %x3
  %x5 = lshr i3 %x4, %x3
  ret i3 %x5
}
=>
define i3 @foo(i3 %0) {
  %x1 = sub i3 0, %0
  ret i3 %x1
}
Transformation doesn't verify!
ERROR: Value mismatch

Example:
i3 %0 = #x5 (5, -3)

Source:
i3 %x1 = #x3 (3)
i1 %x2 = #x1 (1)
i3 %x3 = #x1 (1)
i3 %x4 = #x1 (1)
i3 %x5 = #x0 (0)

Target:
i3 %x1 = #x3 (3)
Source value: #x0 (0)
Target value: #x3 (3)

Summary:
  0 correct transformations
  1 incorrect transformations
  0 errors