Rollup merge of #115972 - RalfJung:const-consistency, r=oli-obk

rename mir::Constant -> mir::ConstOperand, mir::ConstKind -> mir::Const

Also, be more consistent with the `to/eval_bits` methods... we had some that take a type and some that take a size, and then sometimes the one that takes a type is called `bits_for_ty`.

Turns out that `ty::Const`/`mir::ConstKind` carry their type with them, so we don't need to even pass the type to those `eval_bits` functions at all.

However this is not properly consistent yet: in `ty` we have most of the methods on `ty::Const`, but in `mir` we have them on `mir::ConstKind`. And indeed those two types are the ones that correspond to each other. So `mir::ConstantKind` should actually be renamed to `mir::Const`. But what to do with `mir::Constant`? It carries around a span, that's really more like a constant operand that appears as a MIR operand... it's more suited for `syntax.rs` than `consts.rs`, but the bigger question is, which name should it get if we want to align the `mir` and `ty` types? `ConstOperand`? `ConstOp`? `Literal`? It's not a literal but it has a field called `literal` so it would at least be consistently wrong-ish...

``@oli-obk`` any ideas?

src/constant.rs

@@ -64,9 +64,9 @@ pub(crate) fn codegen_tls_ref<'tcx>(
 
 pub(crate) fn eval_mir_constant<'tcx>(
     fx: &FunctionCx<'_, '_, 'tcx>,
-    constant: &Constant<'tcx>,
+    constant: &ConstOperand<'tcx>,
 ) -> (ConstValue<'tcx>, Ty<'tcx>) {
-    let cv = fx.monomorphize(constant.literal);
+    let cv = fx.monomorphize(constant.const_);
     // This cannot fail because we checked all required_consts in advance.
     let val = cv
         .eval(fx.tcx, ty::ParamEnv::reveal_all(), Some(constant.span))
@@ -76,7 +76,7 @@ pub(crate) fn eval_mir_constant<'tcx>(
 
 pub(crate) fn codegen_constant_operand<'tcx>(
     fx: &mut FunctionCx<'_, '_, 'tcx>,
-    constant: &Constant<'tcx>,
+    constant: &ConstOperand<'tcx>,
 ) -> CValue<'tcx> {
     let (const_val, ty) = eval_mir_constant(fx, constant);
     codegen_const_value(fx, const_val, ty)

src/inline_asm.rs

@@ -252,8 +252,8 @@ pub(crate) fn codegen_inline_asm<'tcx>(
                 CInlineAsmOperand::Const { value }
             }
             InlineAsmOperand::SymFn { ref value } => {
-                let literal = fx.monomorphize(value.literal);
-                if let ty::FnDef(def_id, args) = *literal.ty().kind() {
+                let const_ = fx.monomorphize(value.const_);
+                if let ty::FnDef(def_id, args) = *const_.ty().kind() {
                     let instance = ty::Instance::resolve_for_fn_ptr(
                         fx.tcx,
                         ty::ParamEnv::reveal_all(),