gmh5225 / xpass

A collection of experimental optimizing passes for LLVM

XPASS - An experimental LLVM pass

This is an experimental optimizing pass for LLVM, named MathPeephole. This pass performs the following transforms.

• a/b + c/d -> (ad + bc) / (bd)
• x/y + z > a/b + c -> (xb - ay) / (yb) + z > c
• a/b + c > d -> b < 0 ? (a - b * (d - c) < 0) : (-(a - b * (d - c)) < 0)
• w sqrt(x) + y > z -> w >= 0 ? ((z < y) | (wwx > (z-y)(z-y))) : ((z <= y) & (wwx < (z-y)(z-y)))

This project is based on the llvm-tutor package developed by Andrzej Warzyński.

Running the passes

clang-14 -S -emit-llvm -O1 -ffast-math example.c -o example.ll
opt -load-pass-plugin=libMathPeephole.so -passes=math-peephole example.ll -S -o example.opt.ll
clang-14 -O1 -ffast-math example.opt.ll -o example

Please see wiki for examples of the transforms.