Separate between normal evaluated consts and type-system consts

Type system consts (consts that participate in the type system, e.g. const generic params) have special properties: they must have strict equality independent of the user. For example, unions are not possible there. Therefore they are stored as a `ValTree`, a very simple representation that is good, mostly, for comparing things.

General consts can be anything (almost) - arbitrary bytes, even uninit bytes. They are stored like all consts previously were (in the type-system's `Const`), with bytes memory, in a new type called `Allocation` (named borrowed from rustc, although it isn't exactly accurate because in r-a it can represent multiple allocations).

The trigger for this change was a new requirement from rustc_type_ir, that type-system `Const` will be able to represent as a `ValTree`.

Author: ChayimFriedman2

Cargo.toml

@@ -127,7 +127,7 @@ object = { version = "0.36.7", default-features = false, features = [
     "macho",
     "pe",
 ] }
-postcard = {version = "1.1.3", features = ["alloc"]}
+postcard = { version = "1.1.3", features = ["alloc"] }
 process-wrap = { version = "8.2.1", features = ["std"] }
 pulldown-cmark-to-cmark = "10.0.4"
 pulldown-cmark = { version = "0.9.6", default-features = false }
@@ -186,7 +186,10 @@ hashbrown = { version = "0.14.*", features = [
 elided_lifetimes_in_paths = "warn"
 explicit_outlives_requirements = "warn"
 unsafe_op_in_unsafe_fn = "warn"
-unexpected_cfgs = { level = "warn", check-cfg = ['cfg(bootstrap)', "cfg(no_salsa_async_drops)"] }
+unexpected_cfgs = { level = "warn", check-cfg = [
+    'cfg(bootstrap)',
+    "cfg(no_salsa_async_drops)",
+] }
 unused_extern_crates = "warn"
 unused_lifetimes = "warn"
 unreachable_pub = "warn"

crates/hir-def/src/hir.rs

@@ -21,7 +21,7 @@ use std::fmt;
 use hir_expand::{MacroDefId, name::Name};
 use intern::Symbol;
 use la_arena::Idx;
-use rustc_apfloat::ieee::{Half as f16, Quad as f128};
+use rustc_apfloat::ieee::{Double, Half, Quad, Single};
 use syntax::ast;
 use type_ref::TypeRefId;
 
@@ -94,19 +94,19 @@ impl FloatTypeWrapper {
         Self(sym)
     }
 
-    pub fn to_f128(&self) -> f128 {
+    pub fn to_f128(&self) -> Quad {
         self.0.as_str().parse().unwrap_or_default()
     }
 
-    pub fn to_f64(&self) -> f64 {
+    pub fn to_f64(&self) -> Double {
         self.0.as_str().parse().unwrap_or_default()
     }
 
-    pub fn to_f32(&self) -> f32 {
+    pub fn to_f32(&self) -> Single {
         self.0.as_str().parse().unwrap_or_default()
     }
 
-    pub fn to_f16(&self) -> f16 {
+    pub fn to_f16(&self) -> Half {
         self.0.as_str().parse().unwrap_or_default()
     }
 }