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

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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
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7 changed files with 209 additions and 176 deletions
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214
compiler/rustc_codegen_llvm/src/builder/autodiff.rs
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@ -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);