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Rollup merge of #139351 - EnzymeAD:autodiff-batching2, r=oli-obk

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Autodiff batching2

~I will rebase it once my first PR landed.~ done.
This autodiff batch mode is more similar to scalar autodiff, since it still only takes one shadow argument.
However, that argument is supposed to be `width` times larger.

r? `@oli-obk`

Tracking:

- https://github.com/rust-lang/rust/issues/124509
This commit is contained in:
Matthias Krüger 2025-04-17 21:53:23 +02:00 • committed by GitHub
commit 87a163523f
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6 changed files with 220 additions and 28 deletions
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40
compiler/rustc_ast/src/expand/autodiff_attrs.rs
View file

@ -50,8 +50,16 @@ pub enum DiffActivity {
/// with it.
Dual,
/// Forward Mode, Compute derivatives for this input/output and *overwrite* the shadow argument
/// with it. It expects the shadow argument to be `width` times larger than the original
/// input/output.
Dualv,
/// Forward Mode, Compute derivatives for this input/output and *overwrite* the shadow argument
/// with it. Drop the code which updates the original input/output for maximum performance.
DualOnly,
/// Forward Mode, Compute derivatives for this input/output and *overwrite* the shadow argument
/// with it. Drop the code which updates the original input/output for maximum performance.
/// It expects the shadow argument to be `width` times larger than the original input/output.
DualvOnly,
/// Reverse Mode, Compute derivatives for this &T or *T input and *add* it to the shadow argument.
Duplicated,
/// Reverse Mode, Compute derivatives for this &T or *T input and *add* it to the shadow argument.
@ -59,7 +67,15 @@ pub enum DiffActivity {
DuplicatedOnly,
/// All Integers must be Const, but these are used to mark the integer which represents the
/// length of a slice/vec. This is used for safety checks on slices.
FakeActivitySize,
/// The integer (if given) specifies the size of the slice element in bytes.
FakeActivitySize(Option<u32>),
}
impl DiffActivity {
pub fn is_dual_or_const(&self) -> bool {
use DiffActivity::*;
matches!(self, |Dual| DualOnly | Dualv | DualvOnly | Const)
}
}
/// We generate one of these structs for each `#[autodiff(...)]` attribute.
#[derive(Clone, Eq, PartialEq, Encodable, Decodable, Debug, HashStable_Generic)]
@ -131,11 +147,7 @@ pub fn valid_ret_activity(mode: DiffMode, activity: DiffActivity) -> bool {
match mode {
DiffMode::Error => false,
DiffMode::Source => false,
DiffMode::Forward => {
activity == DiffActivity::Dual
|| activity == DiffActivity::DualOnly
|| activity == DiffActivity::Const
}
DiffMode::Forward => activity.is_dual_or_const(),
DiffMode::Reverse => {
activity == DiffActivity::Const
|| activity == DiffActivity::Active
@ -153,10 +165,8 @@ pub fn valid_ret_activity(mode: DiffMode, activity: DiffActivity) -> bool {
pub fn valid_ty_for_activity(ty: &P<Ty>, activity: DiffActivity) -> bool {
use DiffActivity::*;
// It's always allowed to mark something as Const, since we won't compute derivatives wrt. it.
if matches!(activity, Const) {
return true;
}
if matches!(activity, Dual | DualOnly) {
// Dual variants also support all types.
if activity.is_dual_or_const() {
return true;
}
// FIXME(ZuseZ4) We should make this more robust to also
@ -172,9 +182,7 @@ pub fn valid_input_activity(mode: DiffMode, activity: DiffActivity) -> bool {
return match mode {
DiffMode::Error => false,
DiffMode::Source => false,
DiffMode::Forward => {
matches!(activity, Dual | DualOnly | Const)
}
DiffMode::Forward => activity.is_dual_or_const(),
DiffMode::Reverse => {
matches!(activity, Active | ActiveOnly | Duplicated | DuplicatedOnly | Const)
}
@ -189,10 +197,12 @@ impl Display for DiffActivity {
DiffActivity::Active => write!(f, "Active"),
DiffActivity::ActiveOnly => write!(f, "ActiveOnly"),
DiffActivity::Dual => write!(f, "Dual"),
DiffActivity::Dualv => write!(f, "Dualv"),
DiffActivity::DualOnly => write!(f, "DualOnly"),
DiffActivity::DualvOnly => write!(f, "DualvOnly"),
DiffActivity::Duplicated => write!(f, "Duplicated"),
DiffActivity::DuplicatedOnly => write!(f, "DuplicatedOnly"),
DiffActivity::FakeActivitySize => write!(f, "FakeActivitySize"),
DiffActivity::FakeActivitySize(s) => write!(f, "FakeActivitySize({:?})", s),
}
}
}
@ -220,7 +230,9 @@ impl FromStr for DiffActivity {
"ActiveOnly" => Ok(DiffActivity::ActiveOnly),
"Const" => Ok(DiffActivity::Const),
"Dual" => Ok(DiffActivity::Dual),
"Dualv" => Ok(DiffActivity::Dualv),
"DualOnly" => Ok(DiffActivity::DualOnly),
"DualvOnly" => Ok(DiffActivity::DualvOnly),
"Duplicated" => Ok(DiffActivity::Duplicated),
"DuplicatedOnly" => Ok(DiffActivity::DuplicatedOnly),
_ => Err(()),

23
compiler/rustc_builtin_macros/src/autodiff.rs
View file

@ -799,8 +799,19 @@ mod llvm_enzyme {
d_inputs.push(shadow_arg.clone());
}
}
DiffActivity::Dual | DiffActivity::DualOnly => {
for i in 0..x.width {
DiffActivity::Dual
| DiffActivity::DualOnly
| DiffActivity::Dualv
| DiffActivity::DualvOnly => {
// the *v variants get lowered to enzyme_dupv and enzyme_dupnoneedv, which cause
// Enzyme to not expect N arguments, but one argument (which is instead larger).
let iterations =
if matches!(activity, DiffActivity::Dualv | DiffActivity::DualvOnly) {
1
} else {
x.width
};
for i in 0..iterations {
let mut shadow_arg = arg.clone();
let old_name = if let PatKind::Ident(_, ident, _) = arg.pat.kind {
ident.name
@ -823,7 +834,7 @@ mod llvm_enzyme {
DiffActivity::Const => {
// Nothing to do here.
}
DiffActivity::None | DiffActivity::FakeActivitySize => {
DiffActivity::None | DiffActivity::FakeActivitySize(_) => {
panic!("Should not happen");
}
}
@ -887,8 +898,8 @@ mod llvm_enzyme {
}
};
if let DiffActivity::Dual = x.ret_activity {
let kind = if x.width == 1 {
if matches!(x.ret_activity, DiffActivity::Dual | DiffActivity::Dualv) {
let kind = if x.width == 1 || matches!(x.ret_activity, DiffActivity::Dualv) {
// Dual can only be used for f32/f64 ret.
// In that case we return now a tuple with two floats.
TyKind::Tup(thin_vec![ty.clone(), ty.clone()])
@ -903,7 +914,7 @@ mod llvm_enzyme {
let ty = P(rustc_ast::Ty { kind, id: ty.id, span: ty.span, tokens: None });
d_decl.output = FnRetTy::Ty(ty);
}
if let DiffActivity::DualOnly = x.ret_activity {
if matches!(x.ret_activity, DiffActivity::DualOnly | DiffActivity::DualvOnly) {
// No need to change the return type,
// we will just return the shadow in place of the primal return.
// However, if we have a width > 1, then we don't return -> T, but -> [T; width]

2
compiler/rustc_codegen_llvm/src/builder.rs
View file

@ -123,7 +123,7 @@ impl<'a, 'll, CX: Borrow<SCx<'ll>>> GenericBuilder<'a, 'll, CX> {
/// Empty string, to be used where LLVM expects an instruction name, indicating
/// that the instruction is to be left unnamed (i.e. numbered, in textual IR).
// FIXME(eddyb) pass `&CStr` directly to FFI once it's a thin pointer.
const UNNAMED: *const c_char = c"".as_ptr();
pub(crate) const UNNAMED: *const c_char = c"".as_ptr();
impl<'ll, CX: Borrow<SCx<'ll>>> BackendTypes for GenericBuilder<'_, 'll, CX> {
type Value = <GenericCx<'ll, CX> as BackendTypes>::Value;

38
compiler/rustc_codegen_llvm/src/builder/autodiff.rs
View file

@ -10,7 +10,7 @@ use rustc_middle::bug;
use tracing::{debug, trace};
use crate::back::write::llvm_err;
use crate::builder::SBuilder;
use crate::builder::{SBuilder, UNNAMED};
use crate::context::SimpleCx;
use crate::declare::declare_simple_fn;
use crate::errors::{AutoDiffWithoutEnable, LlvmError};
@ -51,6 +51,7 @@ fn has_sret(fnc: &Value) -> bool {
// using iterators and peek()?
fn match_args_from_caller_to_enzyme<'ll>(
cx: &SimpleCx<'ll>,
builder: &SBuilder<'ll, 'll>,
width: u32,
args: &mut Vec<&'ll llvm::Value>,
inputs: &[DiffActivity],
@ -78,7 +79,9 @@ fn match_args_from_caller_to_enzyme<'ll>(
let enzyme_const = cx.create_metadata("enzyme_const".to_string()).unwrap();
let enzyme_out = cx.create_metadata("enzyme_out".to_string()).unwrap();
let enzyme_dup = cx.create_metadata("enzyme_dup".to_string()).unwrap();
let enzyme_dupv = cx.create_metadata("enzyme_dupv".to_string()).unwrap();
let enzyme_dupnoneed = cx.create_metadata("enzyme_dupnoneed".to_string()).unwrap();
let enzyme_dupnoneedv = cx.create_metadata("enzyme_dupnoneedv".to_string()).unwrap();
while activity_pos < inputs.len() {
let diff_activity = inputs[activity_pos as usize];
@ -90,13 +93,34 @@ fn match_args_from_caller_to_enzyme<'ll>(
DiffActivity::Active => (enzyme_out, false),
DiffActivity::ActiveOnly => (enzyme_out, false),
DiffActivity::Dual => (enzyme_dup, true),
DiffActivity::Dualv => (enzyme_dupv, true),
DiffActivity::DualOnly => (enzyme_dupnoneed, true),
DiffActivity::DualvOnly => (enzyme_dupnoneedv, true),
DiffActivity::Duplicated => (enzyme_dup, true),
DiffActivity::DuplicatedOnly => (enzyme_dupnoneed, true),
DiffActivity::FakeActivitySize => (enzyme_const, false),
DiffActivity::FakeActivitySize(_) => (enzyme_const, false),
};
let outer_arg = outer_args[outer_pos];
args.push(cx.get_metadata_value(activity));
if matches!(diff_activity, DiffActivity::Dualv) {
let next_outer_arg = outer_args[outer_pos + 1];
let elem_bytes_size: u64 = match inputs[activity_pos + 1] {
DiffActivity::FakeActivitySize(Some(s)) => s.into(),
_ => bug!("incorrect Dualv handling recognized."),
};
// stride: sizeof(T) * n_elems.
// n_elems is the next integer.
// Now we multiply `4 * next_outer_arg` to get the stride.
let mul = unsafe {
llvm::LLVMBuildMul(
builder.llbuilder,
cx.get_const_i64(elem_bytes_size),
next_outer_arg,
UNNAMED,
)
};
args.push(mul);
}
args.push(outer_arg);
if duplicated {
// We know that duplicated args by construction have a following argument,
@ -114,7 +138,7 @@ fn match_args_from_caller_to_enzyme<'ll>(
} else {
let next_activity = inputs[activity_pos + 1];
// We analyze the MIR types and add this dummy activity if we visit a slice.
next_activity == DiffActivity::FakeActivitySize
matches!(next_activity, DiffActivity::FakeActivitySize(_))
}
};
if slice {
@ -125,7 +149,10 @@ fn match_args_from_caller_to_enzyme<'ll>(
// int2 >= int1, which means the shadow vector is large enough to store the gradient.
assert_eq!(cx.type_kind(next_outer_ty), TypeKind::Integer);
for i in 0..(width as usize) {
let iterations =
if matches!(diff_activity, DiffActivity::Dualv) { 1 } else { width as usize };
for i in 0..iterations {
let next_outer_arg2 = outer_args[outer_pos + 2 * (i + 1)];
let next_outer_ty2 = cx.val_ty(next_outer_arg2);
assert_eq!(cx.type_kind(next_outer_ty2), TypeKind::Pointer);
@ -136,7 +163,7 @@ fn match_args_from_caller_to_enzyme<'ll>(
}
args.push(cx.get_metadata_value(enzyme_const));
args.push(next_outer_arg);
outer_pos += 2 + 2 * width as usize;
outer_pos += 2 + 2 * iterations;
activity_pos += 2;
} else {
// A duplicated pointer will have the following two outer_fn arguments:
@ -360,6 +387,7 @@ fn generate_enzyme_call<'ll>(
let outer_args: Vec<&llvm::Value> = get_params(outer_fn);
match_args_from_caller_to_enzyme(
&cx,
&builder,
attrs.width,
&mut args,
&attrs.input_activity,

32
compiler/rustc_monomorphize/src/partitioning/autodiff.rs
View file

@ -2,7 +2,7 @@ use rustc_ast::expand::autodiff_attrs::{AutoDiffItem, DiffActivity};
use rustc_hir::def_id::LOCAL_CRATE;
use rustc_middle::bug;
use rustc_middle::mir::mono::MonoItem;
use rustc_middle::ty::{self, Instance, Ty, TyCtxt};
use rustc_middle::ty::{self, Instance, PseudoCanonicalInput, Ty, TyCtxt, TypingEnv};
use rustc_symbol_mangling::symbol_name_for_instance_in_crate;
use tracing::{debug, trace};
@ -22,23 +22,51 @@ fn adjust_activity_to_abi<'tcx>(tcx: TyCtxt<'tcx>, fn_ty: Ty<'tcx>, da: &mut Vec
for (i, ty) in sig.inputs().iter().enumerate() {
if let Some(inner_ty) = ty.builtin_deref(true) {
if inner_ty.is_slice() {
// Now we need to figure out the size of each slice element in memory to allow
// safety checks and usability improvements in the backend.
let sty = match inner_ty.builtin_index() {
Some(sty) => sty,
None => {
panic!("slice element type unknown");
}
};
let pci = PseudoCanonicalInput {
typing_env: TypingEnv::fully_monomorphized(),
value: sty,
};
let layout = tcx.layout_of(pci);
let elem_size = match layout {
Ok(layout) => layout.size,
Err(_) => {
bug!("autodiff failed to compute slice element size");
}
};
let elem_size: u32 = elem_size.bytes() as u32;
// We know that the length will be passed as extra arg.
if !da.is_empty() {
// We are looking at a slice. The length of that slice will become an
// extra integer on llvm level. Integers are always const.
// However, if the slice get's duplicated, we want to know to later check the
// size. So we mark the new size argument as FakeActivitySize.
// There is one FakeActivitySize per slice, so for convenience we store the
// slice element size in bytes in it. We will use the size in the backend.
let activity = match da[i] {
DiffActivity::DualOnly
| DiffActivity::Dual
| DiffActivity::Dualv
| DiffActivity::DuplicatedOnly
| DiffActivity::Duplicated => DiffActivity::FakeActivitySize,
| DiffActivity::Duplicated => {
DiffActivity::FakeActivitySize(Some(elem_size))
}
DiffActivity::Const => DiffActivity::Const,
_ => bug!("unexpected activity for ptr/ref"),
};
new_activities.push(activity);
new_positions.push(i + 1);
}
continue;
}
}

113
tests/codegen/autodiffv2.rs Normal file
View file

@ -0,0 +1,113 @@
//@ compile-flags: -Zautodiff=Enable -C opt-level=3 -Clto=fat
//@ no-prefer-dynamic
//@ needs-enzyme
//
// In Enzyme, we test against a large range of LLVM versions (5+) and don't have overly many
// breakages. One benefit is that we match the IR generated by Enzyme only after running it
// through LLVM's O3 pipeline, which will remove most of the noise.
// However, our integration test could also be affected by changes in how rustc lowers MIR into
// LLVM-IR, which could cause additional noise and thus breakages. If that's the case, we should
// reduce this test to only match the first lines and the ret instructions.
//
// The function tested here has 4 inputs and 5 outputs, so we could either call forward-mode
// autodiff 4 times, or reverse mode 5 times. Since a forward-mode call is usually faster than
// reverse mode, we prefer it here. This file also tests a new optimization (batch mode), which
// allows us to call forward-mode autodiff only once, and get all 5 outputs in a single call.
//
// We support 2 different batch modes. `d_square2` has the same interface as scalar forward-mode,
// but each shadow argument is `width` times larger (thus 16 and 20 elements here).
// `d_square3` instead takes `width` (4) shadow arguments, which are all the same size as the
// original function arguments.
//
// FIXME(autodiff): We currently can't test `d_square1` and `d_square3` in the same file, since they
// generate the same dummy functions which get merged by LLVM, breaking pieces of our pipeline which
// try to rewrite the dummy functions later. We should consider to change to pure declarations both
// in our frontend and in the llvm backend to avoid these issues.
#![feature(autodiff)]
use std::autodiff::autodiff;
#[no_mangle]
//#[autodiff(d_square1, Forward, Dual, Dual)]
#[autodiff(d_square2, Forward, 4, Dualv, Dualv)]
#[autodiff(d_square3, Forward, 4, Dual, Dual)]
fn square(x: &[f32], y: &mut [f32]) {
assert!(x.len() >= 4);
assert!(y.len() >= 5);
y[0] = 4.3 * x[0] + 1.2 * x[1] + 3.4 * x[2] + 2.1 * x[3];
y[1] = 2.3 * x[0] + 4.5 * x[1] + 1.7 * x[2] + 6.4 * x[3];
y[2] = 1.1 * x[0] + 3.3 * x[1] + 2.5 * x[2] + 4.7 * x[3];
y[3] = 5.2 * x[0] + 1.4 * x[1] + 2.6 * x[2] + 3.8 * x[3];
y[4] = 1.0 * x[0] + 2.0 * x[1] + 3.0 * x[2] + 4.0 * x[3];
}
fn main() {
let x1 = std::hint::black_box(vec![0.0, 1.0, 2.0, 3.0]);
let dx1 = std::hint::black_box(vec![1.0; 12]);
let z1 = std::hint::black_box(vec![1.0, 0.0, 0.0, 0.0]);
let z2 = std::hint::black_box(vec![0.0, 1.0, 0.0, 0.0]);
let z3 = std::hint::black_box(vec![0.0, 0.0, 1.0, 0.0]);
let z4 = std::hint::black_box(vec![0.0, 0.0, 0.0, 1.0]);
let z5 = std::hint::black_box(vec![
1.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0, 0.0, 0.0, 0.0, 1.0,
]);
let mut y1 = std::hint::black_box(vec![0.0; 5]);
let mut y2 = std::hint::black_box(vec![0.0; 5]);
let mut y3 = std::hint::black_box(vec![0.0; 5]);
let mut y4 = std::hint::black_box(vec![0.0; 5]);
let mut y5 = std::hint::black_box(vec![0.0; 5]);
let mut y6 = std::hint::black_box(vec![0.0; 5]);
let mut dy1_1 = std::hint::black_box(vec![0.0; 5]);
let mut dy1_2 = std::hint::black_box(vec![0.0; 5]);
let mut dy1_3 = std::hint::black_box(vec![0.0; 5]);
let mut dy1_4 = std::hint::black_box(vec![0.0; 5]);
let mut dy2 = std::hint::black_box(vec![0.0; 20]);
let mut dy3_1 = std::hint::black_box(vec![0.0; 5]);
let mut dy3_2 = std::hint::black_box(vec![0.0; 5]);
let mut dy3_3 = std::hint::black_box(vec![0.0; 5]);
let mut dy3_4 = std::hint::black_box(vec![0.0; 5]);
// scalar.
//d_square1(&x1, &z1, &mut y1, &mut dy1_1);
//d_square1(&x1, &z2, &mut y2, &mut dy1_2);
//d_square1(&x1, &z3, &mut y3, &mut dy1_3);
//d_square1(&x1, &z4, &mut y4, &mut dy1_4);
// assert y1 == y2 == y3 == y4
//for i in 0..5 {
// assert_eq!(y1[i], y2[i]);
// assert_eq!(y1[i], y3[i]);
// assert_eq!(y1[i], y4[i]);
//}
// batch mode A)
d_square2(&x1, &z5, &mut y5, &mut dy2);
// assert y1 == y2 == y3 == y4 == y5
//for i in 0..5 {
// assert_eq!(y1[i], y5[i]);
//}
// batch mode B)
d_square3(&x1, &z1, &z2, &z3, &z4, &mut y6, &mut dy3_1, &mut dy3_2, &mut dy3_3, &mut dy3_4);
for i in 0..5 {
assert_eq!(y5[i], y6[i]);
}
for i in 0..5 {
assert_eq!(dy2[0..5][i], dy3_1[i]);
assert_eq!(dy2[5..10][i], dy3_2[i]);
assert_eq!(dy2[10..15][i], dy3_3[i]);
assert_eq!(dy2[15..20][i], dy3_4[i]);
}
}