[all-commits] [llvm/llvm-project] b2165f: [CostModel] Account for power-2 urem in funnel shi...

[David Green via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: b2165f214efab833a4b1a9e8268b1030fc5ebaeb
      https://github.com/llvm/llvm-project/commit/b2165f214efab833a4b1a9e8268b1030fc5ebaeb
  Author: David Green <david.green at arm.com>
  Date:   2025-02-13 (Thu, 13 Feb 2025)

  Changed paths:
    M llvm/include/llvm/CodeGen/BasicTTIImpl.h
    M llvm/test/Analysis/CostModel/AArch64/fshl.ll
    M llvm/test/Analysis/CostModel/AArch64/fshr.ll
    M llvm/test/Analysis/CostModel/AArch64/sve-intrinsics.ll
    M llvm/test/Analysis/CostModel/ARM/intrinsic-cost-kinds.ll

  Log Message:
  -----------
  [CostModel] Account for power-2 urem in funnel shift costs (#127037)

As can be seen in https://godbolt.org/z/qvMqY79cK, a urem by a power-2
constant will be code-generated as an And of a mask. The cost model for
funnel shifts tries to account for that by passing OP_PowerOf2 as the
operand info for the second operand. As far as I can tell returning a
lower cost for urem with a OP_PowerOf2 is only implemented on X86
though.

This patch short-cuts that by calling getArithmeticInstrCost(And, ..)
directly when we know the typesize will be a power-of-2. This is an
alternative to the patch in #126912 which is a more general solution for
power-2 udiv/urem costs, this more narrowly just fixes funnel shifts.



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