bjoernager/rust
bjoernager/rust
1
Fork 0
Code Issues Pull requests Activity

Rollup merge of #138627 - EnzymeAD:autodiff-cleanups, r=oli-obk

Browse source 
Autodiff cleanups

Splitting out some cleanups to reduce the size of my batching PR and simplify ``@haenoe`` 's [PR](https://github.com/rust-lang/rust/pull/138314).

r? ``@oli-obk``

Tracking:

- https://github.com/rust-lang/rust/issues/124509
This commit is contained in:
Matthias Krüger 2025-03-21 15:48:55 +01:00 • committed by GitHub
commit 0c594da55f
No known key found for this signature in database
GPG key ID: B5690EEEBB952194
7 changed files with 209 additions and 176 deletions
Download patch file Download diff file Expand all files Collapse all files

153
compiler/rustc_builtin_macros/src/autodiff.rs
View file

@ -26,6 +26,16 @@ mod llvm_enzyme {
use crate::errors;
pub(crate) fn outer_normal_attr(
kind: &P<rustc_ast::NormalAttr>,
id: rustc_ast::AttrId,
span: Span,
) -> rustc_ast::Attribute {
let style = rustc_ast::AttrStyle::Outer;
let kind = rustc_ast::AttrKind::Normal(kind.clone());
rustc_ast::Attribute { kind, id, style, span }
}
// If we have a default `()` return type or explicitley `()` return type,
// then we often can skip doing some work.
fn has_ret(ty: &FnRetTy) -> bool {
@ -224,20 +234,8 @@ mod llvm_enzyme {
.filter(|a| **a == DiffActivity::Active || **a == DiffActivity::ActiveOnly)
.count() as u32;
let (d_sig, new_args, idents, errored) = gen_enzyme_decl(ecx, &sig, &x, span);
let new_decl_span = d_sig.span;
let d_body = gen_enzyme_body(
ecx,
&x,
n_active,
&sig,
&d_sig,
primal,
&new_args,
span,
sig_span,
new_decl_span,
idents,
errored,
ecx, &x, n_active, &sig, &d_sig, primal, &new_args, span, sig_span, idents, errored,
);
let d_ident = first_ident(&meta_item_vec[0]);
@ -270,36 +268,39 @@ mod llvm_enzyme {
};
let inline_never_attr = P(ast::NormalAttr { item: inline_item, tokens: None });
let new_id = ecx.sess.psess.attr_id_generator.mk_attr_id();
let attr: ast::Attribute = ast::Attribute {
kind: ast::AttrKind::Normal(rustc_ad_attr.clone()),
id: new_id,
style: ast::AttrStyle::Outer,
span,
};
let attr = outer_normal_attr(&rustc_ad_attr, new_id, span);
let new_id = ecx.sess.psess.attr_id_generator.mk_attr_id();
let inline_never: ast::Attribute = ast::Attribute {
kind: ast::AttrKind::Normal(inline_never_attr),
id: new_id,
style: ast::AttrStyle::Outer,
span,
};
let inline_never = outer_normal_attr(&inline_never_attr, new_id, span);
// We're avoid duplicating the attributes `#[rustc_autodiff]` and `#[inline(never)]`.
fn same_attribute(attr: &ast::AttrKind, item: &ast::AttrKind) -> bool {
match (attr, item) {
(ast::AttrKind::Normal(a), ast::AttrKind::Normal(b)) => {
let a = &a.item.path;
let b = &b.item.path;
a.segments.len() == b.segments.len()
&& a.segments.iter().zip(b.segments.iter()).all(|(a, b)| a.ident == b.ident)
}
_ => false,
}
}
// Don't add it multiple times:
let orig_annotatable: Annotatable = match item {
Annotatable::Item(ref mut iitem) => {
if !iitem.attrs.iter().any(|a| a.id == attr.id) {
if !iitem.attrs.iter().any(|a| same_attribute(&a.kind, &attr.kind)) {
iitem.attrs.push(attr);
}
if !iitem.attrs.iter().any(|a| a.id == inline_never.id) {
if !iitem.attrs.iter().any(|a| same_attribute(&a.kind, &inline_never.kind)) {
iitem.attrs.push(inline_never.clone());
}
Annotatable::Item(iitem.clone())
}
Annotatable::AssocItem(ref mut assoc_item, i @ Impl) => {
if !assoc_item.attrs.iter().any(|a| a.id == attr.id) {
if !assoc_item.attrs.iter().any(|a| same_attribute(&a.kind, &attr.kind)) {
assoc_item.attrs.push(attr);
}
if !assoc_item.attrs.iter().any(|a| a.id == inline_never.id) {
if !assoc_item.attrs.iter().any(|a| same_attribute(&a.kind, &inline_never.kind)) {
assoc_item.attrs.push(inline_never.clone());
}
Annotatable::AssocItem(assoc_item.clone(), i)
@ -314,13 +315,7 @@ mod llvm_enzyme {
delim: rustc_ast::token::Delimiter::Parenthesis,
tokens: ts,
});
let d_attr: ast::Attribute = ast::Attribute {
kind: ast::AttrKind::Normal(rustc_ad_attr.clone()),
id: new_id,
style: ast::AttrStyle::Outer,
span,
};
let d_attr = outer_normal_attr(&rustc_ad_attr, new_id, span);
let d_annotatable = if is_impl {
let assoc_item: AssocItemKind = ast::AssocItemKind::Fn(asdf);
let d_fn = P(ast::AssocItem {
@ -361,30 +356,27 @@ mod llvm_enzyme {
ty
}
/// We only want this function to type-check, since we will replace the body
/// later on llvm level. Using `loop {}` does not cover all return types anymore,
/// so instead we build something that should pass. We also add a inline_asm
/// line, as one more barrier for rustc to prevent inlining of this function.
/// FIXME(ZuseZ4): We still have cases of incorrect inlining across modules, see
/// <https://github.com/EnzymeAD/rust/issues/173>, so this isn't sufficient.
/// It also triggers an Enzyme crash if we due to a bug ever try to differentiate
/// this function (which should never happen, since it is only a placeholder).
/// Finally, we also add back_box usages of all input arguments, to prevent rustc
/// from optimizing any arguments away.
fn gen_enzyme_body(
// Will generate a body of the type:
// ```
// {
// unsafe {
// asm!("NOP");
// }
// ::core::hint::black_box(primal(args));
// ::core::hint::black_box((args, ret));
// <This part remains to be done by following function>
// }
// ```
fn init_body_helper(
ecx: &ExtCtxt<'_>,
x: &AutoDiffAttrs,
n_active: u32,
sig: &ast::FnSig,
d_sig: &ast::FnSig,
span: Span,
primal: Ident,
new_names: &[String],
span: Span,
sig_span: Span,
new_decl_span: Span,
idents: Vec<Ident>,
idents: &[Ident],
errored: bool,
) -> P<ast::Block> {
) -> (P<ast::Block>, P<ast::Expr>, P<ast::Expr>, P<ast::Expr>) {
let blackbox_path = ecx.std_path(&[sym::hint, sym::black_box]);
let noop = ast::InlineAsm {
asm_macro: ast::AsmMacro::Asm,
@ -433,6 +425,51 @@ mod llvm_enzyme {
}
body.stmts.push(ecx.stmt_semi(black_box_remaining_args));
(body, primal_call, black_box_primal_call, blackbox_call_expr)
}
/// We only want this function to type-check, since we will replace the body
/// later on llvm level. Using `loop {}` does not cover all return types anymore,
/// so instead we manually build something that should pass the type checker.
/// We also add a inline_asm line, as one more barrier for rustc to prevent inlining
/// or const propagation. inline_asm will also triggers an Enzyme crash if due to another
/// bug would ever try to accidentially differentiate this placeholder function body.
/// Finally, we also add back_box usages of all input arguments, to prevent rustc
/// from optimizing any arguments away.
fn gen_enzyme_body(
ecx: &ExtCtxt<'_>,
x: &AutoDiffAttrs,
n_active: u32,
sig: &ast::FnSig,
d_sig: &ast::FnSig,
primal: Ident,
new_names: &[String],
span: Span,
sig_span: Span,
idents: Vec<Ident>,
errored: bool,
) -> P<ast::Block> {
let new_decl_span = d_sig.span;
// Just adding some default inline-asm and black_box usages to prevent early inlining
// and optimizations which alter the function signature.
//
// The bb_primal_call is the black_box call of the primal function. We keep it around,
// since it has the convenient property of returning the type of the primal function,
// Remember, we only care to match types here.
// No matter which return we pick, we always wrap it into a std::hint::black_box call,
// to prevent rustc from propagating it into the caller.
let (mut body, primal_call, bb_primal_call, bb_call_expr) = init_body_helper(
ecx,
span,
primal,
new_names,
sig_span,
new_decl_span,
&idents,
errored,
);
if !has_ret(&d_sig.decl.output) {
// there is no return type that we have to match, () works fine.
return body;
@ -444,7 +481,7 @@ mod llvm_enzyme {
if primal_ret && n_active == 0 && x.mode.is_rev() {
// We only have the primal ret.
body.stmts.push(ecx.stmt_expr(black_box_primal_call));
body.stmts.push(ecx.stmt_expr(bb_primal_call));
return body;
}
@ -536,11 +573,11 @@ mod llvm_enzyme {
return body;
}
[arg] => {
ret = ecx.expr_call(new_decl_span, blackbox_call_expr, thin_vec![arg.clone()]);
ret = ecx.expr_call(new_decl_span, bb_call_expr, thin_vec![arg.clone()]);
}
args => {
let ret_tuple: P<ast::Expr> = ecx.expr_tuple(span, args.into());
ret = ecx.expr_call(new_decl_span, blackbox_call_expr, thin_vec![ret_tuple]);
ret = ecx.expr_call(new_decl_span, bb_call_expr, thin_vec![ret_tuple]);
}
}
assert!(has_ret(&d_sig.decl.output));
@ -553,7 +590,7 @@ mod llvm_enzyme {
ecx: &ExtCtxt<'_>,
span: Span,
primal: Ident,
idents: Vec<Ident>,
idents: &[Ident],
) -> P<ast::Expr> {
let has_self = idents.len() > 0 && idents[0].name == kw::SelfLower;
if has_self {

214
compiler/rustc_codegen_llvm/src/builder/autodiff.rs
View file

@ -28,6 +28,113 @@ fn get_params(fnc: &Value) -> Vec<&Value> {
}
}
fn match_args_from_caller_to_enzyme<'ll>(
cx: &SimpleCx<'ll>,
args: &mut Vec<&'ll llvm::Value>,
inputs: &[DiffActivity],
outer_args: &[&'ll llvm::Value],
) {
debug!("matching autodiff arguments");
// We now handle the issue that Rust level arguments not always match the llvm-ir level
// arguments. A slice, `&[f32]`, for example, is represented as a pointer and a length on
// llvm-ir level. The number of activities matches the number of Rust level arguments, so we
// need to match those.
// FIXME(ZuseZ4): This logic is a bit more complicated than it should be, can we simplify it
// using iterators and peek()?
let mut outer_pos: usize = 0;
let mut activity_pos = 0;
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_dupnoneed = cx.create_metadata("enzyme_dupnoneed".to_string()).unwrap();
while activity_pos < inputs.len() {
let diff_activity = inputs[activity_pos as usize];
// Duplicated arguments received a shadow argument, into which enzyme will write the
// gradient.
let (activity, duplicated): (&Metadata, bool) = match diff_activity {
DiffActivity::None => panic!("not a valid input activity"),
DiffActivity::Const => (enzyme_const, false),
DiffActivity::Active => (enzyme_out, false),
DiffActivity::ActiveOnly => (enzyme_out, false),
DiffActivity::Dual => (enzyme_dup, true),
DiffActivity::DualOnly => (enzyme_dupnoneed, true),
DiffActivity::Duplicated => (enzyme_dup, true),
DiffActivity::DuplicatedOnly => (enzyme_dupnoneed, true),
DiffActivity::FakeActivitySize => (enzyme_const, false),
};
let outer_arg = outer_args[outer_pos];
args.push(cx.get_metadata_value(activity));
args.push(outer_arg);
if duplicated {
// We know that duplicated args by construction have a following argument,
// so this can not be out of bounds.
let next_outer_arg = outer_args[outer_pos + 1];
let next_outer_ty = cx.val_ty(next_outer_arg);
// FIXME(ZuseZ4): We should add support for Vec here too, but it's less urgent since
// vectors behind references (&Vec<T>) are already supported. Users can not pass a
// Vec by value for reverse mode, so this would only help forward mode autodiff.
let slice = {
if activity_pos + 1 >= inputs.len() {
// If there is no arg following our ptr, it also can't be a slice,
// since that would lead to a ptr, int pair.
false
} 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
}
};
if slice {
// A duplicated slice will have the following two outer_fn arguments:
// (..., ptr1, int1, ptr2, int2, ...). We add the following llvm-ir to our __enzyme call:
// (..., metadata! enzyme_dup, ptr, ptr, int1, ...).
// FIXME(ZuseZ4): We will upstream a safety check later which asserts that
// int2 >= int1, which means the shadow vector is large enough to store the gradient.
assert!(unsafe {
llvm::LLVMRustGetTypeKind(next_outer_ty) == llvm::TypeKind::Integer
});
let next_outer_arg2 = outer_args[outer_pos + 2];
let next_outer_ty2 = cx.val_ty(next_outer_arg2);
assert!(unsafe {
llvm::LLVMRustGetTypeKind(next_outer_ty2) == llvm::TypeKind::Pointer
});
let next_outer_arg3 = outer_args[outer_pos + 3];
let next_outer_ty3 = cx.val_ty(next_outer_arg3);
assert!(unsafe {
llvm::LLVMRustGetTypeKind(next_outer_ty3) == llvm::TypeKind::Integer
});
args.push(next_outer_arg2);
args.push(cx.get_metadata_value(enzyme_const));
args.push(next_outer_arg);
outer_pos += 4;
activity_pos += 2;
} else {
// A duplicated pointer will have the following two outer_fn arguments:
// (..., ptr, ptr, ...). We add the following llvm-ir to our __enzyme call:
// (..., metadata! enzyme_dup, ptr, ptr, ...).
if matches!(diff_activity, DiffActivity::Duplicated | DiffActivity::DuplicatedOnly)
{
assert!(
unsafe { llvm::LLVMRustGetTypeKind(next_outer_ty) }
== llvm::TypeKind::Pointer
);
}
// In the case of Dual we don't have assumptions, e.g. f32 would be valid.
args.push(next_outer_arg);
outer_pos += 2;
activity_pos += 1;
}
} else {
// We do not differentiate with resprect to this argument.
// We already added the metadata and argument above, so just increase the counters.
outer_pos += 1;
activity_pos += 1;
}
}
}
/// When differentiating `fn_to_diff`, take a `outer_fn` and generate another
/// function with expected naming and calling conventions[^1] which will be
/// discovered by the enzyme LLVM pass and its body populated with the differentiated
@ -43,9 +150,6 @@ fn generate_enzyme_call<'ll>(
outer_fn: &'ll Value,
attrs: AutoDiffAttrs,
) {
let inputs = attrs.input_activity;
let output = attrs.ret_activity;
// We have to pick the name depending on whether we want forward or reverse mode autodiff.
let mut ad_name: String = match attrs.mode {
DiffMode::Forward => "__enzyme_fwddiff",
@ -132,111 +236,13 @@ fn generate_enzyme_call<'ll>(
let mut args = Vec::with_capacity(num_args as usize + 1);
args.push(fn_to_diff);
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_dupnoneed = cx.create_metadata("enzyme_dupnoneed".to_string()).unwrap();
let enzyme_primal_ret = cx.create_metadata("enzyme_primal_return".to_string()).unwrap();
match output {
DiffActivity::Dual => {
args.push(cx.get_metadata_value(enzyme_primal_ret));
}
DiffActivity::Active => {
args.push(cx.get_metadata_value(enzyme_primal_ret));
}
_ => {}
if matches!(attrs.ret_activity, DiffActivity::Dual | DiffActivity::Active) {
args.push(cx.get_metadata_value(enzyme_primal_ret));
}
debug!("matching autodiff arguments");
// We now handle the issue that Rust level arguments not always match the llvm-ir level
// arguments. A slice, `&[f32]`, for example, is represented as a pointer and a length on
// llvm-ir level. The number of activities matches the number of Rust level arguments, so we
// need to match those.
// FIXME(ZuseZ4): This logic is a bit more complicated than it should be, can we simplify it
// using iterators and peek()?
let mut outer_pos: usize = 0;
let mut activity_pos = 0;
let outer_args: Vec<&llvm::Value> = get_params(outer_fn);
while activity_pos < inputs.len() {
let diff_activity = inputs[activity_pos as usize];
// Duplicated arguments received a shadow argument, into which enzyme will write the
// gradient.
let (activity, duplicated): (&Metadata, bool) = match diff_activity {
DiffActivity::None => panic!("not a valid input activity"),
DiffActivity::Const => (enzyme_const, false),
DiffActivity::Active => (enzyme_out, false),
DiffActivity::ActiveOnly => (enzyme_out, false),
DiffActivity::Dual => (enzyme_dup, true),
DiffActivity::DualOnly => (enzyme_dupnoneed, true),
DiffActivity::Duplicated => (enzyme_dup, true),
DiffActivity::DuplicatedOnly => (enzyme_dupnoneed, true),
DiffActivity::FakeActivitySize => (enzyme_const, false),
};
let outer_arg = outer_args[outer_pos];
args.push(cx.get_metadata_value(activity));
args.push(outer_arg);
if duplicated {
// We know that duplicated args by construction have a following argument,
// so this can not be out of bounds.
let next_outer_arg = outer_args[outer_pos + 1];
let next_outer_ty = cx.val_ty(next_outer_arg);
// FIXME(ZuseZ4): We should add support for Vec here too, but it's less urgent since
// vectors behind references (&Vec<T>) are already supported. Users can not pass a
// Vec by value for reverse mode, so this would only help forward mode autodiff.
let slice = {
if activity_pos + 1 >= inputs.len() {
// If there is no arg following our ptr, it also can't be a slice,
// since that would lead to a ptr, int pair.
false
} 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
}
};
if slice {
// A duplicated slice will have the following two outer_fn arguments:
// (..., ptr1, int1, ptr2, int2, ...). We add the following llvm-ir to our __enzyme call:
// (..., metadata! enzyme_dup, ptr, ptr, int1, ...).
// FIXME(ZuseZ4): We will upstream a safety check later which asserts that
// int2 >= int1, which means the shadow vector is large enough to store the gradient.
assert!(llvm::LLVMRustGetTypeKind(next_outer_ty) == llvm::TypeKind::Integer);
let next_outer_arg2 = outer_args[outer_pos + 2];
let next_outer_ty2 = cx.val_ty(next_outer_arg2);
assert!(llvm::LLVMRustGetTypeKind(next_outer_ty2) == llvm::TypeKind::Pointer);
let next_outer_arg3 = outer_args[outer_pos + 3];
let next_outer_ty3 = cx.val_ty(next_outer_arg3);
assert!(llvm::LLVMRustGetTypeKind(next_outer_ty3) == llvm::TypeKind::Integer);
args.push(next_outer_arg2);
args.push(cx.get_metadata_value(enzyme_const));
args.push(next_outer_arg);
outer_pos += 4;
activity_pos += 2;
} else {
// A duplicated pointer will have the following two outer_fn arguments:
// (..., ptr, ptr, ...). We add the following llvm-ir to our __enzyme call:
// (..., metadata! enzyme_dup, ptr, ptr, ...).
if matches!(
diff_activity,
DiffActivity::Duplicated | DiffActivity::DuplicatedOnly
) {
assert!(
llvm::LLVMRustGetTypeKind(next_outer_ty) == llvm::TypeKind::Pointer
);
}
// In the case of Dual we don't have assumptions, e.g. f32 would be valid.
args.push(next_outer_arg);
outer_pos += 2;
activity_pos += 1;
}
} else {
// We do not differentiate with resprect to this argument.
// We already added the metadata and argument above, so just increase the counters.
outer_pos += 1;
activity_pos += 1;
}
}
match_args_from_caller_to_enzyme(&cx, &mut args, &attrs.input_activity, &outer_args);
let call = builder.call(enzyme_ty, ad_fn, &args, None);

6
compiler/rustc_codegen_ssa/src/codegen_attrs.rs
View file

@ -790,16 +790,10 @@ fn autodiff_attrs(tcx: TyCtxt<'_>, id: DefId) -> Option<AutoDiffAttrs> {
// check for exactly one autodiff attribute on placeholder functions.
// There should only be one, since we generate a new placeholder per ad macro.
// FIXME(ZuseZ4): re-enable this check. Currently we add multiple, which doesn't cause harm but
// looks strange e.g. under cargo-expand.
let attr = match &attrs[..] {
[] => return None,
[attr] => attr,
// These two attributes are the same and unfortunately duplicated due to a previous bug.
[attr, _attr2] => attr,
_ => {
//FIXME(ZuseZ4): Once we fixed our parser, we should also prohibit the two-attribute
//branch above.
span_bug!(attrs[1].span(), "cg_ssa: rustc_autodiff should only exist once per source");
}
};

6
tests/pretty/autodiff_forward.pp
View file

@ -53,7 +53,7 @@ pub fn df2(x: &[f64], bx: &[f64], y: f64) -> f64 {
pub fn f3(x: &[f64], y: f64) -> f64 {
::core::panicking::panic("not implemented")
}
#[rustc_autodiff(ForwardFirst, Dual, Const, Const,)]
#[rustc_autodiff(Forward, Dual, Const, Const,)]
#[inline(never)]
pub fn df3(x: &[f64], bx: &[f64], y: f64) -> f64 {
unsafe { asm!("NOP", options(pure, nomem)); };
@ -73,10 +73,6 @@ pub fn df4() {
}
#[rustc_autodiff]
#[inline(never)]
#[rustc_autodiff]
#[inline(never)]
#[rustc_autodiff]
#[inline(never)]
pub fn f5(x: &[f64], y: f64) -> f64 {
::core::panicking::panic("not implemented")
}

2
tests/pretty/autodiff_forward.rs
View file

@ -19,7 +19,7 @@ pub fn f2(x: &[f64], y: f64) -> f64 {
unimplemented!()
}
#[autodiff(df3, ForwardFirst, Dual, Const, Const)]
#[autodiff(df3, Forward, Dual, Const, Const)]
pub fn f3(x: &[f64], y: f64) -> f64 {
unimplemented!()
}

2
tests/pretty/autodiff_reverse.pp
View file

@ -51,7 +51,7 @@ pub fn df2() {
pub fn f3(x: &[f64], y: f64) -> f64 {
::core::panicking::panic("not implemented")
}
#[rustc_autodiff(ReverseFirst, Duplicated, Const, Active,)]
#[rustc_autodiff(Reverse, Duplicated, Const, Active,)]
#[inline(never)]
pub fn df3(x: &[f64], dx: &mut [f64], y: f64, dret: f64) -> f64 {
unsafe { asm!("NOP", options(pure, nomem)); };

2
tests/pretty/autodiff_reverse.rs
View file

@ -18,7 +18,7 @@ pub fn f1(x: &[f64], y: f64) -> f64 {
#[autodiff(df2, Reverse)]
pub fn f2() {}
#[autodiff(df3, ReverseFirst, Duplicated, Const, Active)]
#[autodiff(df3, Reverse, Duplicated, Const, Active)]
pub fn f3(x: &[f64], y: f64) -> f64 {
unimplemented!()
}