[all-commits] [llvm/llvm-project] b1d5d7: [VPlan] Don't use the legacy cost model for loop c...

[John Brawn via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: b1d5d7e3237ac5be660f82c71ec7323d6db7b724
      https://github.com/llvm/llvm-project/commit/b1d5d7e3237ac5be660f82c71ec7323d6db7b724
  Author: John Brawn <john.brawn at arm.com>
  Date:   2026-06-03 (Wed, 03 Jun 2026)

  Changed paths:
    M llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
    M llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp
    M llvm/test/Transforms/LoopVectorize/AArch64/cmp_cost.ll
    M llvm/test/Transforms/LoopVectorize/AArch64/conditional-branches-cost.ll
    M llvm/test/Transforms/LoopVectorize/AArch64/fully-unrolled-cost.ll
    M llvm/test/Transforms/LoopVectorize/AArch64/scalable-vectorization-cost-tuning.ll
    M llvm/test/Transforms/LoopVectorize/ARM/mve-icmpcost.ll
    M llvm/test/Transforms/LoopVectorize/RISCV/low-trip-count.ll
    M llvm/test/Transforms/LoopVectorize/X86/CostModel/vpinstruction-cost.ll
    M llvm/test/Transforms/LoopVectorize/X86/consecutive-ptr-uniforms.ll
    M llvm/test/Transforms/LoopVectorize/X86/cost-model.ll
    M llvm/test/Transforms/LoopVectorize/X86/reduction-small-size.ll

  Log Message:
  -----------
  [VPlan] Don't use the legacy cost model for loop conditions (#156864)

The current behaviour of using the legacy cost model for instructions
that compute the loop exit condition gets the wrong result when the loop
has been transformed to use a different exit condition, e.g. when have
tail-folded predicated vectorization the exit condition is based on the
predicate vector.

Fix this by adding cost computation for BranchOnCount and removing the
restriction on computing the cost for scalar ICmp/FCmp, and removing the
use of the legacy cost model for loop exit conditions.

This causes quite a lot of changes to expected output in tests. Some of
these are just changes to the -debug output, others are choosing a
different VF due to previously over or under-estimating the cost, and in
others the minimum trip count has changed as we now compute the cost for
compares in the middle block.



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