Rollup merge of #144197 - KMJ-007:type-tree, r=ZuseZ4

2025-09-28T16:13:11+00:00

TypeTree support in autodiff # TypeTrees for Autodiff ## What are TypeTrees? Memory layout descriptors for Enzyme. Tell Enzyme exactly how types are structured in memory so it can compute derivatives efficiently. ## Structure ```rust TypeTree(Vec) Type { offset: isize, // byte offset (-1 = everywhere) size: usize, // size in bytes kind: Kind, // Float, Integer, Pointer, etc. child: TypeTree // nested structure } ``` ## Example: `fn compute(x: &f32, data: &[f32]) -> f32` **Input 0: `x: &f32`** ```rust TypeTree(vec![Type { offset: -1, size: 8, kind: Pointer, child: TypeTree(vec![Type { offset: -1, size: 4, kind: Float, child: TypeTree::new() }]) }]) ``` **Input 1: `data: &[f32]`** ```rust TypeTree(vec![Type { offset: -1, size: 8, kind: Pointer, child: TypeTree(vec![Type { offset: -1, size: 4, kind: Float, // -1 = all elements child: TypeTree::new() }]) }]) ``` **Output: `f32`** ```rust TypeTree(vec![Type { offset: -1, size: 4, kind: Float, child: TypeTree::new() }]) ``` ## Why Needed? - Enzyme can't deduce complex type layouts from LLVM IR - Prevents slow memory pattern analysis - Enables correct derivative computation for nested structures - Tells Enzyme which bytes are differentiable vs metadata ## What Enzyme Does With This Information: Without TypeTrees (current state): ```llvm ; Enzyme sees generic LLVM IR: define float ``@distance(ptr*`` %p1, ptr* %p2) { ; Has to guess what these pointers point to ; Slow analysis of all memory operations ; May miss optimization opportunities } ``` With TypeTrees (our implementation): ```llvm define "enzyme_type"="{[]:Float@float}" float ``@distance(`` ptr "enzyme_type"="{[]:Pointer}" %p1, ptr "enzyme_type"="{[]:Pointer}" %p2 ) { ; Enzyme knows exact type layout ; Can generate efficient derivative code directly } ``` # TypeTrees - Offset and -1 Explained ## Type Structure ```rust Type { offset: isize, // WHERE this type starts size: usize, // HOW BIG this type is kind: Kind, // WHAT KIND of data (Float, Int, Pointer) child: TypeTree // WHAT'S INSIDE (for pointers/containers) } ``` ## Offset Values ### Regular Offset (0, 4, 8, etc.) **Specific byte position within a structure** ```rust struct Point { x: f32, // offset 0, size 4 y: f32, // offset 4, size 4 id: i32, // offset 8, size 4 } ``` TypeTree for `&Point` (internal representation): ```rust TypeTree(vec![ Type { offset: 0, size: 4, kind: Float }, // x at byte 0 Type { offset: 4, size: 4, kind: Float }, // y at byte 4 Type { offset: 8, size: 4, kind: Integer } // id at byte 8 ]) ``` Generates LLVM: ```llvm "enzyme_type"="{[]:Float@float}" ``` ### Offset -1 (Special: "Everywhere") **Means "this pattern repeats for ALL elements"** #### Example 1: Array `[f32; 100]` ```rust TypeTree(vec![Type { offset: -1, // ALL positions size: 4, // each f32 is 4 bytes kind: Float, // every element is float }]) ``` Instead of listing 100 separate Types with offsets `0,4,8,12...396` #### Example 2: Slice `&[i32]` ```rust // Pointer to slice data TypeTree(vec![Type { offset: -1, size: 8, kind: Pointer, child: TypeTree(vec![Type { offset: -1, // ALL slice elements size: 4, // each i32 is 4 bytes kind: Integer }]) }]) ``` #### Example 3: Mixed Structure ```rust struct Container { header: i64, // offset 0 data: [f32; 1000], // offset 8, but elements use -1 } ``` ```rust TypeTree(vec![ Type { offset: 0, size: 8, kind: Integer }, // header Type { offset: 8, size: 4000, kind: Pointer, child: TypeTree(vec![Type { offset: -1, size: 4, kind: Float // ALL array elements }]) } ]) ```

Use `LLVMDisposeTargetMachine`

2025-09-25T08:10:55+00:00

Add self-profile events for target-machine creation

2025-09-21T11:37:15+00:00

These code paths are surprisingly hot in the `large-workspace` benchmark; it would be handy to see some detailed timings and execution counts.

autodiff: Add basic TypeTree with NoTT flag

2025-09-19T04:02:19+00:00

Signed-off-by: Karan Janthe

Move target machine command-line quoting from C++ to Rust

2025-09-18T05:25:25+00:00

Make llvm_enzyme a regular cargo feature

2025-09-15T15:31:56+00:00

This makes it clearer that it is set by the build system rather than by the rustc that compiles the current rustc. It also avoids bootstrap needing to pass --check-cfg llvm_enzyme to rustc.

Remove want_summary argument from prepare_thin

2025-09-06T18:37:23+00:00

It is always false nowadays. ThinLTO summary writing is instead done by llvm_optimize.

Remove thin_link_data method from ThinBufferMethods

2025-09-06T18:37:23+00:00

It is only used within cg_llvm.

Ensure fat LTO doesn't merge everything into the allocator module

2025-09-06T13:31:41+00:00

Special case allocator module submission to avoid special casing it elsewhere

2025-09-04T08:21:10+00:00

A lot of places had special handling just in case they would get an allocator module even though most of these places could never get one or would have a trivial implementation for the allocator module. Moving all handling of the allocator module to a single place simplifies things a fair bit.

rust/compiler/rustc_codegen_llvm/src/back, branch master