[llvm] [GlobalISel][TableGen] Support for typed G_FCONSTANT Imm in MIR-patttern (PR #219563)

[Vikash Gupta via llvm-commits]

vg0204 wrote:

> Why does this need a custom operator? I'd hope you can just write this directly as the new constant instruction by its usual name

As I investigated further we do need something like GIReplaceRegWithConstant buitin type rule (to replace C++ replaceInstWithConstant), as direct G_CONSTANT can be used only in scalar scenario, as there could be case where the IMM need to splatted into a fixed-vector (DstType is Vector). So, we need GIReplaceRegWithConstant capable of handling both scalar/splatted vector case!

I will make a separate PR for that replacing both replaceInstWithConstant/replaceInstWithFConstant with their counter-part builtin rule type

@arsenm , @Pierre-vh does its sound right!

https://github.com/llvm/llvm-project/pull/219563