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Some autodiff cleanups #138345

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merged 2 commits into from
Mar 12, 2025
Merged

Some autodiff cleanups #138345

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ff5a8ad
Explain the actual reason why stripping binders is fine
oli-obk Feb 24, 2025
9882eca
Remove some dead code
oli-obk Mar 11, 2025
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16 changes: 5 additions & 11 deletions compiler/rustc_monomorphize/src/partitioning/autodiff.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -12,21 +12,15 @@ fn adjust_activity_to_abi<'tcx>(tcx: TyCtxt<'tcx>, fn_ty: Ty<'tcx>, da: &mut Vec
if !matches!(fn_ty.kind(), ty::FnDef(..)) {
bug!("expected fn def for autodiff, got {:?}", fn_ty);
}
let fnc_binder: ty::Binder<'_, ty::FnSig<'_>> = fn_ty.fn_sig(tcx);

// If rustc compiles the unmodified primal, we know that this copy of the function
// also has correct lifetimes. We know that Enzyme won't free the shadow too early
// (or actually at all), so let's strip lifetimes when computing the layout.
let x = tcx.instantiate_bound_regions_with_erased(fnc_binder);
// We don't actually pass the types back into the type system.
// All we do is decide how to handle the arguments.
let sig = fn_ty.fn_sig(tcx).skip_binder();

let mut new_activities = vec![];
let mut new_positions = vec![];
for (i, ty) in x.inputs().iter().enumerate() {
for (i, ty) in sig.inputs().iter().enumerate() {
if let Some(inner_ty) = ty.builtin_deref(true) {
if ty.is_fn_ptr() {
// FIXME(ZuseZ4): add a nicer error, or just figure out how to support them,
// since Enzyme itself can handle them.
tcx.dcx().err("function pointers are currently not supported in autodiff");
}
if inner_ty.is_slice() {
// We know that the length will be passed as extra arg.
if !da.is_empty() {
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