clang pragma fp should allow emission of IR arcp flag

[arsenm]

pragma clang fp already exists which enables fast math flags within a scope. It currently supports pragma clang fp contract(value) and pragma clang fp reassociate(on).

I would like this extended to cover other fast math flags, in particular arcp. For something like

float fast_div(float x, float y) {
  #pragma clang fp reciprocal(on)
  return x / y;
}

I would hope to get

float @fast_div(float %, float %y) {
   %0 = fdiv arcp float %x, %y
   ret float %0 
}

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Matt Arsenault (arsenm)

pragma clang fp already exists which enables fast math flags within a scope. It currently supports `pragma clang fp contract(value)` and `pragma clang fp reassociate(on)`.

I would like this extended to cover other fast math flags, in particular arcp. For something like

float fast_div(float x, float y) {
  #pragma clang fp reciprocal(on)
  return x / y;
}

I would hope to get

float @<!-- -->fast_div(float %, float %y) {
   %0 = fdiv arcp float %x, %y
   ret float %0 
}