llvm-project

7b8fd8f3 - [LLVM][SCEV] Look through common vscale multiplicand when simplifying compares. (#141798)

[LLVM][SCEV] Look through common vscale multiplicand when simplifying compares. (#141798) My usecase is simplifying the control flow generated by LoopVectorize when vectorising loops whose tripcount is a function of the runtime vector length. This can be problematic because: * CSE is a pre-LoopVectorize transform and so it's common for an IR function to include several calls to llvm.vscale(). (NOTE: Code generation will typically remove the duplicates) * Pre-LoopVectorize instcombines will rewrite some multiplies as shifts. This leads to a mismatch between VL based maths of the scalar loop and that created for the vector loop, which prevents some obvious simplifications. SCEV does not suffer these issues because it effectively does CSE during construction and shifts are represented as multiplies.