llvm-project

524b1788 - [VPlan] Add BranchOnTwoConds, use for early exit plans. (#172750)

[VPlan] Add BranchOnTwoConds, use for early exit plans. (#172750) This PR introduces a new BranchOnTwoConds VPInstruction, that takes 2 boolean operands and must be placed in a block with 3 successors. If condition I is true, branches to successor I, otherwise falls through to check the next condition. If both conditions are false, branch to the third successor. This new branch recipe is used for early-exit loops, to simplify the representation in VPlan initially, by avoid the need for splitting the middle block early on, in a way that preserves the single-exit block property of regions. All exits still go through the latch block, but they can go to more than 2 successors. This idea was part of one of the original proposals for how to model early exits in VPlan, but at that point in time, there was no good way to handle this during code-gen, and we went with the early split-middle block approach initially. Now that we dissolve regions before ::execute, the new recipe can be lowered nicely after regions have been removed, to a set of VPBBs and BranchOnCond recipes. The initial lowering preserves the original structure with the split middle blocks. Follow-ups will improve the lowering to avoid this splitting, providing performance gains. PR: https://github.com/llvm/llvm-project/pull/172750