diff options
Diffstat (limited to 'compiler/rustc_codegen_llvm/src/builder/autodiff.rs')
| -rw-r--r-- | compiler/rustc_codegen_llvm/src/builder/autodiff.rs | 426 |
1 files changed, 124 insertions, 302 deletions
diff --git a/compiler/rustc_codegen_llvm/src/builder/autodiff.rs b/compiler/rustc_codegen_llvm/src/builder/autodiff.rs index 829b3c513c2..e2df3265f6f 100644 --- a/compiler/rustc_codegen_llvm/src/builder/autodiff.rs +++ b/compiler/rustc_codegen_llvm/src/builder/autodiff.rs @@ -1,40 +1,92 @@ use std::ptr; -use rustc_ast::expand::autodiff_attrs::{AutoDiffAttrs, AutoDiffItem, DiffActivity, DiffMode}; -use rustc_codegen_ssa::ModuleCodegen; +use rustc_ast::expand::autodiff_attrs::{AutoDiffAttrs, DiffActivity, DiffMode}; use rustc_codegen_ssa::common::TypeKind; -use rustc_codegen_ssa::traits::BaseTypeCodegenMethods; -use rustc_errors::FatalError; -use rustc_middle::bug; -use tracing::{debug, trace}; +use rustc_codegen_ssa::traits::{BaseTypeCodegenMethods, BuilderMethods}; +use rustc_middle::ty::{PseudoCanonicalInput, Ty, TyCtxt, TypingEnv}; +use rustc_middle::{bug, ty}; +use tracing::debug; -use crate::back::write::llvm_err; -use crate::builder::{SBuilder, UNNAMED}; +use crate::builder::{Builder, PlaceRef, UNNAMED}; use crate::context::SimpleCx; use crate::declare::declare_simple_fn; -use crate::errors::{AutoDiffWithoutEnable, LlvmError}; -use crate::llvm::AttributePlace::Function; -use crate::llvm::{Metadata, True}; +use crate::llvm; +use crate::llvm::{Metadata, True, Type}; use crate::value::Value; -use crate::{CodegenContext, LlvmCodegenBackend, ModuleLlvm, attributes, llvm}; -fn get_params(fnc: &Value) -> Vec<&Value> { - let param_num = llvm::LLVMCountParams(fnc) as usize; - let mut fnc_args: Vec<&Value> = vec![]; - fnc_args.reserve(param_num); - unsafe { - llvm::LLVMGetParams(fnc, fnc_args.as_mut_ptr()); - fnc_args.set_len(param_num); +pub(crate) fn adjust_activity_to_abi<'tcx>( + tcx: TyCtxt<'tcx>, + fn_ty: Ty<'tcx>, + da: &mut Vec<DiffActivity>, +) { + if !matches!(fn_ty.kind(), ty::FnDef(..)) { + bug!("expected fn def for autodiff, got {:?}", fn_ty); } - fnc_args -} -fn has_sret(fnc: &Value) -> bool { - let num_args = llvm::LLVMCountParams(fnc) as usize; - if num_args == 0 { - false - } else { - unsafe { llvm::LLVMRustHasAttributeAtIndex(fnc, 0, llvm::AttributeKind::StructRet) } + // 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 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(Some(elem_size)) + } + DiffActivity::Const => DiffActivity::Const, + _ => bug!("unexpected activity for ptr/ref"), + }; + new_activities.push(activity); + new_positions.push(i + 1); + } + + continue; + } + } + } + // now add the extra activities coming from slices + // Reverse order to not invalidate the indices + for _ in 0..new_activities.len() { + let pos = new_positions.pop().unwrap(); + let activity = new_activities.pop().unwrap(); + da.insert(pos, activity); } } @@ -48,14 +100,13 @@ fn has_sret(fnc: &Value) -> bool { // 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()? -fn match_args_from_caller_to_enzyme<'ll>( +fn match_args_from_caller_to_enzyme<'ll, 'tcx>( cx: &SimpleCx<'ll>, - builder: &SBuilder<'ll, 'll>, + builder: &mut Builder<'_, 'll, 'tcx>, width: u32, args: &mut Vec<&'ll llvm::Value>, inputs: &[DiffActivity], outer_args: &[&'ll llvm::Value], - has_sret: bool, ) { debug!("matching autodiff arguments"); // We now handle the issue that Rust level arguments not always match the llvm-ir level @@ -67,14 +118,6 @@ fn match_args_from_caller_to_enzyme<'ll>( let mut outer_pos: usize = 0; let mut activity_pos = 0; - if has_sret { - // Then the first outer arg is the sret pointer. Enzyme doesn't know about sret, so the - // inner function will still return something. We increase our outer_pos by one, - // and once we're done with all other args we will take the return of the inner call and - // update the sret pointer with it - outer_pos = 1; - } - let enzyme_const = cx.create_metadata(b"enzyme_const"); let enzyme_out = cx.create_metadata(b"enzyme_out"); let enzyme_dup = cx.create_metadata(b"enzyme_dup"); @@ -193,92 +236,6 @@ fn match_args_from_caller_to_enzyme<'ll>( } } -// On LLVM-IR, we can luckily declare __enzyme_ functions without specifying the input -// arguments. We do however need to declare them with their correct return type. -// We already figured the correct return type out in our frontend, when generating the outer_fn, -// so we can now just go ahead and use that. This is not always trivial, e.g. because sret. -// Beyond sret, this article describes our challenges nicely: -// <https://yorickpeterse.com/articles/the-mess-that-is-handling-structure-arguments-and-returns-in-llvm/> -// I.e. (i32, f32) will get merged into i64, but we don't handle that yet. -fn compute_enzyme_fn_ty<'ll>( - cx: &SimpleCx<'ll>, - attrs: &AutoDiffAttrs, - fn_to_diff: &'ll Value, - outer_fn: &'ll Value, -) -> &'ll llvm::Type { - let fn_ty = cx.get_type_of_global(outer_fn); - let mut ret_ty = cx.get_return_type(fn_ty); - - let has_sret = has_sret(outer_fn); - - if has_sret { - // Now we don't just forward the return type, so we have to figure it out based on the - // primal return type, in combination with the autodiff settings. - let fn_ty = cx.get_type_of_global(fn_to_diff); - let inner_ret_ty = cx.get_return_type(fn_ty); - - let void_ty = unsafe { llvm::LLVMVoidTypeInContext(cx.llcx) }; - if inner_ret_ty == void_ty { - // This indicates that even the inner function has an sret. - // Right now I only look for an sret in the outer function. - // This *probably* needs some extra handling, but I never ran - // into such a case. So I'll wait for user reports to have a test case. - bug!("sret in inner function"); - } - - if attrs.width == 1 { - // Enzyme returns a struct of style: - // `{ original_ret(if requested), float, float, ... }` - let mut struct_elements = vec![]; - if attrs.has_primal_ret() { - struct_elements.push(inner_ret_ty); - } - // Next, we push the list of active floats, since they will be lowered to `enzyme_out`, - // and therefore part of the return struct. - let param_tys = cx.func_params_types(fn_ty); - for (act, param_ty) in attrs.input_activity.iter().zip(param_tys) { - if matches!(act, DiffActivity::Active) { - // Now find the float type at position i based on the fn_ty, - // to know what (f16/f32/f64/...) to add to the struct. - struct_elements.push(param_ty); - } - } - ret_ty = cx.type_struct(&struct_elements, false); - } else { - // First we check if we also have to deal with the primal return. - match attrs.mode { - DiffMode::Forward => match attrs.ret_activity { - DiffActivity::Dual => { - let arr_ty = - unsafe { llvm::LLVMArrayType2(inner_ret_ty, attrs.width as u64 + 1) }; - ret_ty = arr_ty; - } - DiffActivity::DualOnly => { - let arr_ty = - unsafe { llvm::LLVMArrayType2(inner_ret_ty, attrs.width as u64) }; - ret_ty = arr_ty; - } - DiffActivity::Const => { - todo!("Not sure, do we need to do something here?"); - } - _ => { - bug!("unreachable"); - } - }, - DiffMode::Reverse => { - todo!("Handle sret for reverse mode"); - } - _ => { - bug!("unreachable"); - } - } - } - } - - // LLVM can figure out the input types on it's own, so we take a shortcut here. - unsafe { llvm::LLVMFunctionType(ret_ty, ptr::null(), 0, True) } -} - /// 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 @@ -288,11 +245,15 @@ fn compute_enzyme_fn_ty<'ll>( /// [^1]: <https://enzyme.mit.edu/getting_started/CallingConvention/> // FIXME(ZuseZ4): `outer_fn` should include upstream safety checks to // cover some assumptions of enzyme/autodiff, which could lead to UB otherwise. -fn generate_enzyme_call<'ll>( +pub(crate) fn generate_enzyme_call<'ll, 'tcx>( + builder: &mut Builder<'_, 'll, 'tcx>, cx: &SimpleCx<'ll>, fn_to_diff: &'ll Value, - outer_fn: &'ll Value, + outer_name: &str, + ret_ty: &'ll Type, + fn_args: &[&'ll Value], attrs: AutoDiffAttrs, + dest: PlaceRef<'tcx, &'ll Value>, ) { // We have to pick the name depending on whether we want forward or reverse mode autodiff. let mut ad_name: String = match attrs.mode { @@ -302,11 +263,9 @@ fn generate_enzyme_call<'ll>( } .to_string(); - // add outer_fn name to ad_name to make it unique, in case users apply autodiff to multiple + // add outer_name to ad_name to make it unique, in case users apply autodiff to multiple // functions. Unwrap will only panic, if LLVM gave us an invalid string. - let name = llvm::get_value_name(outer_fn); - let outer_fn_name = std::str::from_utf8(&name).unwrap(); - ad_name.push_str(outer_fn_name); + ad_name.push_str(outer_name); // Let us assume the user wrote the following function square: // @@ -316,14 +275,8 @@ fn generate_enzyme_call<'ll>( // %0 = fmul double %x, %x // ret double %0 // } - // ``` - // - // The user now applies autodiff to the function square, in which case fn_to_diff will be `square`. - // Our macro generates the following placeholder code (slightly simplified): // - // ```llvm // define double @dsquare(double %x) { - // ; placeholder code // return 0.0; // } // ``` @@ -340,175 +293,44 @@ fn generate_enzyme_call<'ll>( // ret double %0 // } // ``` - unsafe { - let enzyme_ty = compute_enzyme_fn_ty(cx, &attrs, fn_to_diff, outer_fn); - - // FIXME(ZuseZ4): the CC/Addr/Vis values are best effort guesses, we should look at tests and - // think a bit more about what should go here. - let cc = llvm::LLVMGetFunctionCallConv(outer_fn); - let ad_fn = declare_simple_fn( - cx, - &ad_name, - llvm::CallConv::try_from(cc).expect("invalid callconv"), - llvm::UnnamedAddr::No, - llvm::Visibility::Default, - enzyme_ty, - ); - - // Otherwise LLVM might inline our temporary code before the enzyme pass has a chance to - // do it's work. - let attr = llvm::AttributeKind::NoInline.create_attr(cx.llcx); - attributes::apply_to_llfn(ad_fn, Function, &[attr]); - - // We add a made-up attribute just such that we can recognize it after AD to update - // (no)-inline attributes. We'll then also remove this attribute. - let enzyme_marker_attr = llvm::CreateAttrString(cx.llcx, "enzyme_marker"); - attributes::apply_to_llfn(outer_fn, Function, &[enzyme_marker_attr]); - - // first, remove all calls from fnc - let entry = llvm::LLVMGetFirstBasicBlock(outer_fn); - let br = llvm::LLVMRustGetTerminator(entry); - llvm::LLVMRustEraseInstFromParent(br); - - let last_inst = llvm::LLVMRustGetLastInstruction(entry).unwrap(); - let mut builder = SBuilder::build(cx, entry); - - let num_args = llvm::LLVMCountParams(&fn_to_diff); - let mut args = Vec::with_capacity(num_args as usize + 1); - args.push(fn_to_diff); - - let enzyme_primal_ret = cx.create_metadata(b"enzyme_primal_return"); - if matches!(attrs.ret_activity, DiffActivity::Dual | DiffActivity::Active) { - args.push(cx.get_metadata_value(enzyme_primal_ret)); - } - if attrs.width > 1 { - let enzyme_width = cx.create_metadata(b"enzyme_width"); - args.push(cx.get_metadata_value(enzyme_width)); - args.push(cx.get_const_int(cx.type_i64(), attrs.width as u64)); - } - - let has_sret = has_sret(outer_fn); - 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, - &outer_args, - has_sret, - ); - - let call = builder.call(enzyme_ty, ad_fn, &args, None); - - // This part is a bit iffy. LLVM requires that a call to an inlineable function has some - // metadata attached to it, but we just created this code oota. Given that the - // differentiated function already has partly confusing metadata, and given that this - // affects nothing but the auttodiff IR, we take a shortcut and just steal metadata from the - // dummy code which we inserted at a higher level. - // FIXME(ZuseZ4): Work with Enzyme core devs to clarify what debug metadata issues we have, - // and how to best improve it for enzyme core and rust-enzyme. - let md_ty = cx.get_md_kind_id("dbg"); - if llvm::LLVMRustHasMetadata(last_inst, md_ty) { - let md = llvm::LLVMRustDIGetInstMetadata(last_inst) - .expect("failed to get instruction metadata"); - let md_todiff = cx.get_metadata_value(md); - llvm::LLVMSetMetadata(call, md_ty, md_todiff); - } else { - // We don't panic, since depending on whether we are in debug or release mode, we might - // have no debug info to copy, which would then be ok. - trace!("no dbg info"); - } - - // Now that we copied the metadata, get rid of dummy code. - llvm::LLVMRustEraseInstUntilInclusive(entry, last_inst); - - if cx.val_ty(call) == cx.type_void() || has_sret { - if has_sret { - // This is what we already have in our outer_fn (shortened): - // define void @_foo(ptr <..> sret([32 x i8]) initializes((0, 32)) %0, <...>) { - // %7 = call [4 x double] (...) @__enzyme_fwddiff_foo(ptr @square, metadata !"enzyme_width", i64 4, <...>) - // <Here we are, we want to add the following two lines> - // store [4 x double] %7, ptr %0, align 8 - // ret void - // } - - // now store the result of the enzyme call into the sret pointer. - let sret_ptr = outer_args[0]; - let call_ty = cx.val_ty(call); - if attrs.width == 1 { - assert_eq!(cx.type_kind(call_ty), TypeKind::Struct); - } else { - assert_eq!(cx.type_kind(call_ty), TypeKind::Array); - } - llvm::LLVMBuildStore(&builder.llbuilder, call, sret_ptr); - } - builder.ret_void(); - } else { - builder.ret(call); - } - - // Let's crash in case that we messed something up above and generated invalid IR. - llvm::LLVMRustVerifyFunction( - outer_fn, - llvm::LLVMRustVerifierFailureAction::LLVMAbortProcessAction, - ); - } -} - -pub(crate) fn differentiate<'ll>( - module: &'ll ModuleCodegen<ModuleLlvm>, - cgcx: &CodegenContext<LlvmCodegenBackend>, - diff_items: Vec<AutoDiffItem>, -) -> Result<(), FatalError> { - for item in &diff_items { - trace!("{}", item); + let enzyme_ty = unsafe { llvm::LLVMFunctionType(ret_ty, ptr::null(), 0, True) }; + + // FIXME(ZuseZ4): the CC/Addr/Vis values are best effort guesses, we should look at tests and + // think a bit more about what should go here. + let cc = unsafe { llvm::LLVMGetFunctionCallConv(fn_to_diff) }; + let ad_fn = declare_simple_fn( + cx, + &ad_name, + llvm::CallConv::try_from(cc).expect("invalid callconv"), + llvm::UnnamedAddr::No, + llvm::Visibility::Default, + enzyme_ty, + ); + + let num_args = llvm::LLVMCountParams(&fn_to_diff); + let mut args = Vec::with_capacity(num_args as usize + 1); + args.push(fn_to_diff); + + let enzyme_primal_ret = cx.create_metadata(b"enzyme_primal_return"); + if matches!(attrs.ret_activity, DiffActivity::Dual | DiffActivity::Active) { + args.push(cx.get_metadata_value(enzyme_primal_ret)); } - - let diag_handler = cgcx.create_dcx(); - - let cx = SimpleCx::new(module.module_llvm.llmod(), module.module_llvm.llcx, cgcx.pointer_size); - - // First of all, did the user try to use autodiff without using the -Zautodiff=Enable flag? - if !diff_items.is_empty() - && !cgcx.opts.unstable_opts.autodiff.contains(&rustc_session::config::AutoDiff::Enable) - { - return Err(diag_handler.handle().emit_almost_fatal(AutoDiffWithoutEnable)); - } - - // Here we replace the placeholder code with the actual autodiff code, which calls Enzyme. - for item in diff_items.iter() { - let name = item.source.clone(); - let fn_def: Option<&llvm::Value> = cx.get_function(&name); - let Some(fn_def) = fn_def else { - return Err(llvm_err( - diag_handler.handle(), - LlvmError::PrepareAutoDiff { - src: item.source.clone(), - target: item.target.clone(), - error: "could not find source function".to_owned(), - }, - )); - }; - debug!(?item.target); - let fn_target: Option<&llvm::Value> = cx.get_function(&item.target); - let Some(fn_target) = fn_target else { - return Err(llvm_err( - diag_handler.handle(), - LlvmError::PrepareAutoDiff { - src: item.source.clone(), - target: item.target.clone(), - error: "could not find target function".to_owned(), - }, - )); - }; - - generate_enzyme_call(&cx, fn_def, fn_target, item.attrs.clone()); + if attrs.width > 1 { + let enzyme_width = cx.create_metadata(b"enzyme_width"); + args.push(cx.get_metadata_value(enzyme_width)); + args.push(cx.get_const_int(cx.type_i64(), attrs.width as u64)); } - // FIXME(ZuseZ4): support SanitizeHWAddress and prevent illegal/unsupported opts + match_args_from_caller_to_enzyme( + &cx, + builder, + attrs.width, + &mut args, + &attrs.input_activity, + fn_args, + ); - trace!("done with differentiate()"); + let call = builder.call(enzyme_ty, None, None, ad_fn, &args, None, None); - Ok(()) + builder.store_to_place(call, dest.val); } |