[SPIR-V] Reg2Mem producing unwanted bitcast

[spall]

It seems enabling reg2mem here ( #111026 ) has introduced what looks like a bug, when doing SPIRV codegen. What looks like an unnecessary bitcast is generated. See %9:

    %1 = OpTypeFloat 32
    %2 = OpTypeFunction %1 %1
    %3 = OpTypeInt 32 0
    %4 = OpConstant %3 0
    %5 = OpConstant %1 0
    %6 = OpConstant %1 1
    %8 = OpFunction %1 None %2              ; -- Begin function saturate_float
    %7 = OpFunctionParameter %1
    %12 = OpLabel
    %9 = OpBitcast %3 %4
    %10 = OpExtInst %1 %11 FClamp %7 %5 %6
    OpReturnValue %10
    OpFunctionEnd

saturate-repro.ll :

; this was just taken from the
; llvm/CodeGen/SPIRV/hlsl-intrinsics/saturate.ll test cases.

define noundef float @saturate_float(float noundef %a) {
entry:
  %hlsl.saturate = call float @llvm.spv.saturate.f32(float %a)
  ret float %hlsl.saturate
}

To reproduce this issue:

• build main branch llvm
• cmake command used:

cmake -G Ninja -DCMAKE_BUILD_TYPE=RelWithDebInfo -C <your-path>/llvm-project/clang/cmake/caches/HLSL.cmake -DLLVM_ENABLE_ASSERTIONS=On -DCMAKE_CXX_COMPILER=/usr/bin/clang++ -DCMAKE_C_COMPILER=/usr/bin/clang -DLLVM_USE_LINKER=lld ../llvm

• run test provided above.

 llc -verify-machineinstrs -O0 -mtriple=spirv-unknown-unknown saturate-repro.ll -o -

note: this bitcast seemingly appears in all the CodeGen/SPIRV/hlsl-intrinsics tests.
note: Also see comment I left on #111026

[Keenuts]

Thanks for the issue & repro!
Looking into what @VyacheslavLevytskyy suggested