// Return true iff we think it might be beneficial to turn this alloc instruction
// into a statically allocated global.
// Precondition: we are compiling the init function.
func (fr *frame) shouldStaticallyAllocate(alloc *ssa.Alloc) bool {
// First, see if the allocated type is an array or struct, and if so determine
// the number of elements in the type. If the type is anything else, we
// statically allocate unconditionally.
var numElems int64
switch ty := deref(alloc.Type()).Underlying().(type) {
case *types.Array:
numElems = ty.Len()
case *types.Struct:
numElems = int64(ty.NumFields())
default:
return true
}
// We treat the number of referrers to the alloc instruction as a rough
// proxy for the number of elements initialized. If the data structure
// is densely initialized (> 1/4 elements initialized), enable the
// optimization.
return int64(len(*alloc.Referrers()))*4 > numElems
}
