[llvm] [RISCV][TTI] Use processShuffleMask for shuffle legalization estimate (PR #136191)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `lld-x86_64-ubuntu-fast` running on `as-builder-4` while building `llvm` at step 5 "build-unified-tree".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/33/builds/15276

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 5 (build-unified-tree) failure: build (failure)
...
28.281 [477/10/3470] Linking CXX static library lib/libLLVMLTO.a
30.180 [477/9/3471] Building AMDGPUGenAsmWriter.inc...
31.158 [477/8/3472] Building AMDGPUGenGlobalISel.inc...
31.256 [477/7/3473] Linking CXX executable bin/lli
31.656 [477/6/3474] Building AMDGPUGenAsmMatcher.inc...
31.849 [477/5/3475] Building AMDGPUGenDAGISel.inc...
32.665 [477/4/3476] Building AMDGPUGenInstrInfo.inc...
34.254 [477/3/3477] Building AMDGPUGenRegisterBank.inc...
35.058 [477/2/3478] Building AMDGPUGenRegisterInfo.inc...
37.742 [476/2/3479] Building CXX object lib/Target/RISCV/CMakeFiles/LLVMRISCVCodeGen.dir/RISCVTargetTransformInfo.cpp.o
FAILED: lib/Target/RISCV/CMakeFiles/LLVMRISCVCodeGen.dir/RISCVTargetTransformInfo.cpp.o 
CCACHE_CPP2=yes CCACHE_HASHDIR=yes /usr/bin/ccache /usr/bin/c++ -DGTEST_HAS_RTTI=0 -D_DEBUG -D_GLIBCXX_ASSERTIONS -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/build/lib/Target/RISCV -I/home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/llvm-project/llvm/lib/Target/RISCV -I/home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/build/include -I/home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/llvm-project/llvm/include -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror=date-time -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -pedantic -Wno-long-long -Wimplicit-fallthrough -Wno-uninitialized -Wno-nonnull -Wno-class-memaccess -Wno-redundant-move -Wno-pessimizing-move -Wno-noexcept-type -Wdelete-non-virtual-dtor -Wsuggest-override -Wno-comment -Wno-misleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -ffunction-sections -fdata-sections -O3 -DNDEBUG -fvisibility=hidden  -fno-exceptions -funwind-tables -fno-rtti -UNDEBUG -std=c++17 -MD -MT lib/Target/RISCV/CMakeFiles/LLVMRISCVCodeGen.dir/RISCVTargetTransformInfo.cpp.o -MF lib/Target/RISCV/CMakeFiles/LLVMRISCVCodeGen.dir/RISCVTargetTransformInfo.cpp.o.d -o lib/Target/RISCV/CMakeFiles/LLVMRISCVCodeGen.dir/RISCVTargetTransformInfo.cpp.o -c /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/llvm-project/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp
/home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/llvm-project/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp: In member function ‘llvm::InstructionCost llvm::RISCVTTIImpl::getShuffleCost(llvm::TargetTransformInfo::ShuffleKind, llvm::VectorType*, llvm::ArrayRef<int>, llvm::TargetTransformInfo::TargetCostKind, int, llvm::VectorType*, llvm::ArrayRef<const llvm::Value*>, const llvm::Instruction*) const’:
/home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/llvm-project/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp:710: error: binding reference of type ‘llvm::RISCVTTIImpl&’ to ‘const llvm::RISCVTTIImpl’ discards qualifiers
  710 |           costShuffleViaSplitting(*this, LT.second, FVTp, Mask, CostKind);
      | 
/home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/llvm-project/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp:392: note:   initializing argument 1 of ‘llvm::InstructionCost costShuffleViaSplitting(llvm::RISCVTTIImpl&, llvm::MVT, llvm::VectorType*, llvm::ArrayRef<int>, llvm::TargetTransformInfo::TargetCostKind)’
  392 | static InstructionCost costShuffleViaSplitting(RISCVTTIImpl &TTI, MVT LegalVT,
      | 
/home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/llvm-project/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp: At global scope:
/home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/llvm-project/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp:392: warning: ‘llvm::InstructionCost costShuffleViaSplitting(llvm::RISCVTTIImpl&, llvm::MVT, llvm::VectorType*, llvm::ArrayRef<int>, llvm::TargetTransformInfo::TargetCostKind)’ defined but not used [-Wunused-function]
48.731 [476/1/3480] Building InstCombineTables.inc...
ninja: build stopped: subcommand failed.

```

</details>

https://github.com/llvm/llvm-project/pull/136191