Decouple serde from its derive crate

By not activating the `derive` feature on `serde`, the compilation speed
can be improved by a lot. This is because `serde` can then compile in
parallel to `serde_derive`, allowing it to finish compilation possibly
even before `serde_derive`, unblocking all the crates waiting for
`serde` to start compiling much sooner.

As it turns out the main deciding factor for how long the compile time of a
project is, is primarly determined by the depth of dependencies rather
than the width. In other words, a crate's compile times aren't affected
by how many crates it depends on, but rather by the longest chain of
dependencies that it needs to wait on. In many cases `serde` is part of
that long chain, as it is part of a long chain if the `derive` feature
is active:

`proc-macro2` compile build script > `proc-macro2` run build script >
`proc-macro2` > `quote` > `syn` > `serde_derive` > `serde` >
`serde_json` (or any crate that depends on serde)

By decoupling it from `serde_derive`, the chain is shortened and compile
times get much better.

Check this issue for a deeper elaboration:
serde-rs/serde#2584

For `wasmtime` I'm seeing a reduction from 24.75s to 22.45s when
compiling in `release` mode. This is because wasmtime through `gimli`
has a dependency on `indexmap` which can only start compiling when
`serde` is finished, which you want to happen as early as possible so
some of wasmtime's dependencies can start compiling.

To measure the full effect, the dependencies can't by themselves
activate the `derive` feature. I've upstreamed a patch for
`fxprof-processed-profile` which was the only dependency that activated
it for `wasmtime` (not yet published to crates.io). `wasmtime-cli` and
co. may need patches for their dependencies to see a similar
improvement.

cranelift/codegen/Cargo.toml

@@ -23,7 +23,8 @@ cranelift-control = { workspace = true }
 hashbrown = { workspace = true, features = ["raw"] }
 target-lexicon = { workspace = true }
 log = { workspace = true }
-serde = { version = "1.0.94", features = ["derive"], optional = true }
+serde = { version = "1.0.188", optional = true }
+serde_derive = { version = "1.0.188", optional = true }
 bincode = { version = "1.2.1", optional = true }
 gimli = { workspace = true, features = ["write"], optional = true }
 smallvec = { workspace = true }
@@ -87,6 +88,7 @@ all-arch = [
 # For dependent crates that want to serialize some parts of cranelift
 enable-serde = [
     "serde",
+    "serde_derive",
     "cranelift-entity/enable-serde",
     "regalloc2/enable-serde",
     "smallvec/serde"

cranelift/codegen/meta/src/gen_inst.rs

@@ -502,7 +502,7 @@ fn gen_opcodes(all_inst: &AllInstructions, fmt: &mut Formatter) {
     fmt.line(
         r#"#[cfg_attr(
             feature = "enable-serde",
-            derive(serde::Serialize, serde::Deserialize)
+            derive(serde_derive::Serialize, serde_derive::Deserialize)
         )]"#,
     );
 

cranelift/codegen/src/binemit/mod.rs

@@ -8,7 +8,7 @@ mod stack_map;
 pub use self::stack_map::StackMap;
 use core::fmt;
 #[cfg(feature = "enable-serde")]
-use serde::{Deserialize, Serialize};
+use serde_derive::{Deserialize, Serialize};
 
 /// Offset in bytes from the beginning of the function.
 ///

cranelift/codegen/src/binemit/stack_map.rs

@@ -67,7 +67,10 @@ const NUM_BITS: usize = core::mem::size_of::<Num>() * 8;
 /// live GC references in these slots. We record the `IncomingArg`s in the
 /// callee's stack map.
 #[derive(Clone, Debug, PartialEq, Eq)]
-#[cfg_attr(feature = "enable-serde", derive(serde::Deserialize, serde::Serialize))]
+#[cfg_attr(
+    feature = "enable-serde",
+    derive(serde_derive::Deserialize, serde_derive::Serialize)
+)]
 pub struct StackMap {
     bitmap: Vec<BitSet<Num>>,
     mapped_words: u32,

cranelift/codegen/src/bitset.rs

@@ -12,7 +12,10 @@ use core::ops::{Add, BitOr, Shl, Sub};
 
 /// A small bitset built on a single primitive integer type
 #[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
-#[cfg_attr(feature = "enable-serde", derive(serde::Serialize, serde::Deserialize))]
+#[cfg_attr(
+    feature = "enable-serde",
+    derive(serde_derive::Serialize, serde_derive::Deserialize)
+)]
 pub struct BitSet<T>(pub T);
 
 impl<T> BitSet<T>

cranelift/codegen/src/incremental_cache.rs

@@ -118,7 +118,7 @@ impl std::fmt::Display for CacheKeyHash {
     }
 }
 
-#[derive(serde::Serialize, serde::Deserialize)]
+#[derive(serde_derive::Serialize, serde_derive::Deserialize)]
 struct CachedFunc {
     // Note: The version marker must be first to ensure deserialization stops in case of a version
     // mismatch before attempting to deserialize the actual compiled code.
@@ -139,7 +139,7 @@ struct CacheKey<'a> {
     parameters: CompileParameters,
 }
 
-#[derive(Clone, PartialEq, Hash, serde::Serialize, serde::Deserialize)]
+#[derive(Clone, PartialEq, Hash, serde_derive::Serialize, serde_derive::Deserialize)]
 struct CompileParameters {
     isa: String,
     triple: String,

cranelift/codegen/src/ir/atomic_rmw_op.rs

@@ -2,7 +2,7 @@
 use core::fmt::{self, Display, Formatter};
 use core::str::FromStr;
 #[cfg(feature = "enable-serde")]
-use serde::{Deserialize, Serialize};
+use serde_derive::{Deserialize, Serialize};
 
 #[derive(Clone, Copy, PartialEq, Eq, Debug, Hash)]
 #[cfg_attr(feature = "enable-serde", derive(Serialize, Deserialize))]

cranelift/codegen/src/ir/condcodes.rs

@@ -8,7 +8,7 @@ use core::fmt::{self, Display, Formatter};
 use core::str::FromStr;
 
 #[cfg(feature = "enable-serde")]
-use serde::{Deserialize, Serialize};
+use serde_derive::{Deserialize, Serialize};
 
 /// Common traits of condition codes.
 pub trait CondCode: Copy {

cranelift/codegen/src/ir/constant.rs

@@ -19,7 +19,7 @@ use core::str::{from_utf8, FromStr};
 use cranelift_entity::EntityRef;
 
 #[cfg(feature = "enable-serde")]
-use serde::{Deserialize, Serialize};
+use serde_derive::{Deserialize, Serialize};
 
 /// This type describes the actual constant data. Note that the bytes stored in this structure are
 /// expected to be in little-endian order; this is due to ease-of-use when interacting with

cranelift/codegen/src/ir/dfg.rs

@@ -20,7 +20,7 @@ use core::u16;
 
 use alloc::collections::BTreeMap;
 #[cfg(feature = "enable-serde")]
-use serde::{Deserialize, Serialize};
+use serde_derive::{Deserialize, Serialize};
 use smallvec::SmallVec;
 
 /// Storage for instructions within the DFG.

cranelift/codegen/src/ir/dynamic_type.rs

@@ -7,7 +7,7 @@ use crate::ir::PrimaryMap;
 use crate::ir::Type;
 
 #[cfg(feature = "enable-serde")]
-use serde::{Deserialize, Serialize};
+use serde_derive::{Deserialize, Serialize};
 
 /// A dynamic type object which has a base vector type and a scaling factor.
 #[derive(Clone, PartialEq, Hash)]

cranelift/codegen/src/ir/entities.rs

@@ -23,7 +23,7 @@ use crate::entity::entity_impl;
 use core::fmt;
 use core::u32;
 #[cfg(feature = "enable-serde")]
-use serde::{Deserialize, Serialize};
+use serde_derive::{Deserialize, Serialize};
 
 /// An opaque reference to a [basic block](https://en.wikipedia.org/wiki/Basic_block) in a
 /// [`Function`](super::function::Function).

cranelift/codegen/src/ir/extfunc.rs

@@ -11,7 +11,7 @@ use alloc::vec::Vec;
 use core::fmt;
 use core::str::FromStr;
 #[cfg(feature = "enable-serde")]
-use serde::{Deserialize, Serialize};
+use serde_derive::{Deserialize, Serialize};
 
 use super::function::FunctionParameters;
 

cranelift/codegen/src/ir/extname.rs

@@ -11,7 +11,7 @@ use core::str::FromStr;
 
 use cranelift_entity::EntityRef as _;
 #[cfg(feature = "enable-serde")]
-use serde::{Deserialize, Serialize};
+use serde_derive::{Deserialize, Serialize};
 
 use super::entities::UserExternalNameRef;
 use super::function::FunctionParameters;

cranelift/codegen/src/ir/function.rs

@@ -64,7 +64,10 @@ impl<'de> Deserialize<'de> for VersionMarker {
 /// Function parameters used when creating this function, and that will become applied after
 /// compilation to materialize the final `CompiledCode`.
 #[derive(Clone, PartialEq)]
-#[cfg_attr(feature = "enable-serde", derive(Serialize, Deserialize))]
+#[cfg_attr(
+    feature = "enable-serde",
+    derive(serde_derive::Serialize, serde_derive::Deserialize)
+)]
 pub struct FunctionParameters {
     /// The first `SourceLoc` appearing in the function, serving as a base for every relative
     /// source loc in the function.
@@ -146,7 +149,10 @@ impl FunctionParameters {
 /// Additionally, these fields can be the same for two functions that would be compiled the same
 /// way, and finalized by applying `FunctionParameters` onto their `CompiledCodeStencil`.
 #[derive(Clone, PartialEq, Hash)]
-#[cfg_attr(feature = "enable-serde", derive(Serialize, Deserialize))]
+#[cfg_attr(
+    feature = "enable-serde",
+    derive(serde_derive::Serialize, serde_derive::Deserialize)
+)]
 pub struct FunctionStencil {
     /// A version marker used to ensure that serialized clif ir is never deserialized with a
     /// different version of Cranelift.

cranelift/codegen/src/ir/globalvalue.rs

@@ -6,7 +6,7 @@ use crate::isa::TargetIsa;
 use core::fmt;
 
 #[cfg(feature = "enable-serde")]
-use serde::{Deserialize, Serialize};
+use serde_derive::{Deserialize, Serialize};
 
 /// Information about a global value declaration.
 #[derive(Clone, PartialEq, Hash)]

cranelift/codegen/src/ir/immediates.rs

@@ -12,7 +12,7 @@ use core::ops::{Add, BitAnd, BitOr, BitXor, Div, Mul, Neg, Not, Sub};
 use core::str::FromStr;
 use core::{i32, u32};
 #[cfg(feature = "enable-serde")]
-use serde::{Deserialize, Serialize};
+use serde_derive::{Deserialize, Serialize};
 
 /// Convert a type into a vector of bytes; all implementors in this file must use little-endian
 /// orderings of bytes to match WebAssembly's little-endianness.

cranelift/codegen/src/ir/instructions.rs

@@ -12,7 +12,7 @@ use core::ops::{Deref, DerefMut};
 use core::str::FromStr;
 
 #[cfg(feature = "enable-serde")]
-use serde::{Deserialize, Serialize};
+use serde_derive::{Deserialize, Serialize};
 
 use crate::bitset::BitSet;
 use crate::entity;

cranelift/codegen/src/ir/jumptable.rs

@@ -10,7 +10,7 @@ use core::fmt::{self, Display, Formatter};
 use core::slice::{Iter, IterMut};
 
 #[cfg(feature = "enable-serde")]
-use serde::{Deserialize, Serialize};
+use serde_derive::{Deserialize, Serialize};
 
 /// Contents of a jump table.
 ///

cranelift/codegen/src/ir/known_symbol.rs

@@ -1,7 +1,7 @@
 use core::fmt;
 use core::str::FromStr;
 #[cfg(feature = "enable-serde")]
-use serde::{Deserialize, Serialize};
+use serde_derive::{Deserialize, Serialize};
 
 /// A well-known symbol.
 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]

cranelift/codegen/src/ir/libcall.rs

@@ -7,7 +7,7 @@ use crate::{
 use core::fmt;
 use core::str::FromStr;
 #[cfg(feature = "enable-serde")]
-use serde::{Deserialize, Serialize};
+use serde_derive::{Deserialize, Serialize};
 
 /// The name of a runtime library routine.
 ///

cranelift/codegen/src/ir/memflags.rs

@@ -3,7 +3,7 @@
 use core::fmt;
 
 #[cfg(feature = "enable-serde")]
-use serde::{Deserialize, Serialize};
+use serde_derive::{Deserialize, Serialize};
 
 enum FlagBit {
     Notrap,

cranelift/codegen/src/ir/mod.rs

@@ -26,7 +26,7 @@ mod trapcode;
 pub mod types;
 
 #[cfg(feature = "enable-serde")]
-use serde::{Deserialize, Serialize};
+use serde_derive::{Deserialize, Serialize};
 
 pub use crate::ir::atomic_rmw_op::AtomicRmwOp;
 pub use crate::ir::builder::{

cranelift/codegen/src/ir/sourceloc.rs

@@ -5,7 +5,7 @@
 
 use core::fmt;
 #[cfg(feature = "enable-serde")]
-use serde::{Deserialize, Serialize};
+use serde_derive::{Deserialize, Serialize};
 
 /// A source location.
 ///

cranelift/codegen/src/ir/stackslot.rs

@@ -17,7 +17,7 @@ use crate::ir::{DynamicTypeData, GlobalValueData};
 use crate::ir::types::*;
 
 #[cfg(feature = "enable-serde")]
-use serde::{Deserialize, Serialize};
+use serde_derive::{Deserialize, Serialize};
 
 /// The size of an object on the stack, or the size of a stack frame.
 ///

cranelift/codegen/src/ir/table.rs

@@ -5,7 +5,7 @@ use crate::ir::{GlobalValue, Type};
 use core::fmt;
 
 #[cfg(feature = "enable-serde")]
-use serde::{Deserialize, Serialize};
+use serde_derive::{Deserialize, Serialize};
 
 /// Information about a table declaration.
 #[derive(Clone, PartialEq, Hash)]

cranelift/codegen/src/ir/trapcode.rs

@@ -3,7 +3,7 @@
 use core::fmt::{self, Display, Formatter};
 use core::str::FromStr;
 #[cfg(feature = "enable-serde")]
-use serde::{Deserialize, Serialize};
+use serde_derive::{Deserialize, Serialize};
 
 /// A trap code describing the reason for a trap.
 ///

cranelift/codegen/src/ir/types.rs

@@ -4,7 +4,7 @@ use core::default::Default;
 use core::fmt::{self, Debug, Display, Formatter};
 use cranelift_codegen_shared::constants;
 #[cfg(feature = "enable-serde")]
-use serde::{Deserialize, Serialize};
+use serde_derive::{Deserialize, Serialize};
 use target_lexicon::{PointerWidth, Triple};
 
 /// The type of an SSA value.

cranelift/codegen/src/isa/call_conv.rs

@@ -4,7 +4,7 @@ use core::str;
 use target_lexicon::{CallingConvention, Triple};
 
 #[cfg(feature = "enable-serde")]
-use serde::{Deserialize, Serialize};
+use serde_derive::{Deserialize, Serialize};
 
 /// Calling convention identifiers.
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]