MIR inlining should work with any `ty::FnDef` callee operand, not just constants.

[eddyb]

This code:

rust/src/librustc_mir/transform/inline.rs

Lines 96 to 97 in 994cdd9

	if let TerminatorKind::Call {
	func: Operand::Constant(ref f), .. } = terminator.kind {

should not pattern-match on func, but rather call its ty method to get its type.

What this means is that let f = foo; f(); should inline as well as foo() (but today it doesn't).

cc @nikomatsakis

[nagisa]

Actually it should handle both cases, I think. Handling the func constant is useful when the type has been erased but constant propagation managed to propagate the actual function anyway.

[eddyb]

@nagisa It's type-based today, but it only handles the Operand::Constant case.
While handling function pointer types based on the value would be interesting, it's not done today.

[pvdrz]

Working on this one :)