llvm-project

013f2542 - [LV] Simplify and unify resume value handling for epilogue vec. (#185969)

[LV] Simplify and unify resume value handling for epilogue vec. (#185969) This patch tries to drastically simplify resume value handling for the scalar loop when vectorizing the epilogue. It uses a simpler, uniform approach for updating all resume values in the scalar loop: 1. Create ResumeForEpilogue recipes for all scalar resume phis in the main loop (the epilogue plan will have exactly the same scalar resume phis, in exactly the same order) 2. Update ::execute for ResumeForEpilogue to set the underlying value when executing. This is not super clean, but allows easy lookup of the generated IR value when we update the resume phis in the epilogue. Once we connect the 2 plans together explicitly, this can be removed. 3. Use the list of ResumeForEpilogue VPInstructions from the main loop to update the resume/bypass values from the epilogue. This simplifies the code quite a bit, makes it more robust (should fix https://github.com/llvm/llvm-project/issues/179407) and also fixes a mis-compile in the existing tests (see change in llvm/test/Transforms/LoopVectorize/AArch64/partial-reduce-sub-epilogue-vec.ll, where previously we would incorrectly resume using the start value when the epilogue iteration check failed) In some cases, we get simpler code, due to additional CSE, in some cases the induction end value computations get moved from the epilogue iteration check to the vector preheader. We could try to sink the instructions as cleanup, but it is probably not worth the trouble. Fixes https://github.com/llvm/llvm-project/issues/179407.