[all-commits] [llvm/llvm-project] 831527: [FMV][GlobalOpt] Statically resolve calls to versi...

[Alexandros Lamprineas via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 831527a5ef63d24d056afc92509caf5ceb1d3682
      https://github.com/llvm/llvm-project/commit/831527a5ef63d24d056afc92509caf5ceb1d3682
  Author: Alexandros Lamprineas <alexandros.lamprineas at arm.com>
  Date:   2025-01-17 (Fri, 17 Jan 2025)

  Changed paths:
    M llvm/include/llvm/Analysis/TargetTransformInfo.h
    M llvm/include/llvm/Analysis/TargetTransformInfoImpl.h
    M llvm/include/llvm/TargetParser/AArch64TargetParser.h
    M llvm/lib/Analysis/TargetTransformInfo.cpp
    M llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
    M llvm/lib/Target/AArch64/AArch64TargetTransformInfo.h
    M llvm/lib/TargetParser/AArch64TargetParser.cpp
    M llvm/lib/Transforms/IPO/GlobalOpt.cpp
    A llvm/test/Transforms/GlobalOpt/resolve-fmv-ifunc.ll

  Log Message:
  -----------
  [FMV][GlobalOpt] Statically resolve calls to versioned functions. (#87939)

To deduce whether the optimization is legal we need to compare the target
features between caller and callee versions. The criteria for bypassing
the resolver are the following:

 * If the callee's feature set is a subset of the caller's feature set,
   then the callee is a candidate for direct call.

 * Among such candidates the one of highest priority is the best match
   and it shall be picked, unless there is a version of the callee with
   higher priority than the best match which cannot be picked from a
   higher priority caller (directly or through the resolver).

 * For every higher priority callee version than the best match, there
   is a higher priority caller version whose feature set availability
   is implied by the callee's feature set.

Example:

Callers and Callees are ordered in decreasing priority.
The arrows indicate successful call redirections.

  Caller        Callee      Explanation
=========================================================================
mops+sve2 --+--> mops       all the callee versions are subsets of the
            |               caller but mops has the highest priority
            |
     mops --+    sve2       between mops and default callees, mops wins

      sve        sve        between sve and default callees, sve wins
                            but sve2 does not have a high priority caller

  default -----> default    sve (callee) implies sve (caller),
                            sve2(callee) implies sve (caller),
                            mops(callee) implies mops(caller)



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