Auto merge of #136428 - EnzymeAD:enable-autodiff, r=oli-obk

test building enzyme in CI

1) This PR fixes a significant compile-time regression, by only running the expensive autodiff pipeline, if the users pass the newly introduced Enable value to the `-Zautodiff=` flag. It updates the test(s) accordingly. It gives a nice error if users forget that.
2) It fixes macos support by explicitly linking against the Enzyme build folder. This doesn't cover CI macos yet.
3) It fixes the issue that setting ENZYME_RUNPASS was ignored by enzyme and in fact did not schedule enzyme's opt pass.
4) It also re-enables support for various other values for the autodiff flag, which were ignored since the refactor.
5) I merged some improvements to Enzyme core, which means we do not longer depend on LLVM being build with the Plugin Interface enabled.
6) Unrelated to other fixes, this changes `rustc_autodiff` to `EncodeCrossCrate::Yes`. It is not enough on it's own to enable usage of Enzyme in libraries, but it is for sure a piece of the fixes needed to get this to work.

try-job: x86_64-gnu

r? `@oli-obk`

Tracking:

- https://github.com/rust-lang/rust/issues/124509

5 files changed, 174 insertions, 38 deletions

diff --git a/compiler/rustc_codegen_llvm/src/back/lto.rs b/compiler/rustc_codegen_llvm/src/back/lto.rs
index 3e25b94961b..99906ea7bce 100644
--- a/compiler/rustc_codegen_llvm/src/back/lto.rs
+++ b/compiler/rustc_codegen_llvm/src/back/lto.rs
@@ -586,6 +586,42 @@ fn thin_lto(
     }
 }
 
+fn enable_autodiff_settings(ad: &[config::AutoDiff], module: &mut ModuleCodegen<ModuleLlvm>) {
+    for &val in ad {
+        match val {
+            config::AutoDiff::PrintModBefore => {
+                unsafe { llvm::LLVMDumpModule(module.module_llvm.llmod()) };
+            }
+            config::AutoDiff::PrintPerf => {
+                llvm::set_print_perf(true);
+            }
+            config::AutoDiff::PrintAA => {
+                llvm::set_print_activity(true);
+            }
+            config::AutoDiff::PrintTA => {
+                llvm::set_print_type(true);
+            }
+            config::AutoDiff::Inline => {
+                llvm::set_inline(true);
+            }
+            config::AutoDiff::LooseTypes => {
+                llvm::set_loose_types(false);
+            }
+            config::AutoDiff::PrintSteps => {
+                llvm::set_print(true);
+            }
+            // We handle this below
+            config::AutoDiff::PrintModAfter => {}
+            // This is required and already checked
+            config::AutoDiff::Enable => {}
+        }
+    }
+    // This helps with handling enums for now.
+    llvm::set_strict_aliasing(false);
+    // FIXME(ZuseZ4): Test this, since it was added a long time ago.
+    llvm::set_rust_rules(true);
+}
+
 pub(crate) fn run_pass_manager(
     cgcx: &CodegenContext<LlvmCodegenBackend>,
     dcx: DiagCtxtHandle<'_>,
@@ -604,34 +640,37 @@ pub(crate) fn run_pass_manager(
     let opt_stage = if thin { llvm::OptStage::ThinLTO } else { llvm::OptStage::FatLTO };
     let opt_level = config.opt_level.unwrap_or(config::OptLevel::No);
 
-    // If this rustc version was build with enzyme/autodiff enabled, and if users applied the
-    // `#[autodiff]` macro at least once, then we will later call llvm_optimize a second time.
-    debug!("running llvm pm opt pipeline");
+    // The PostAD behavior is the same that we would have if no autodiff was used.
+    // It will run the default optimization pipeline. If AD is enabled we select
+    // the DuringAD stage, which will disable vectorization and loop unrolling, and
+    // schedule two autodiff optimization + differentiation passes.
+    // We then run the llvm_optimize function a second time, to optimize the code which we generated
+    // in the enzyme differentiation pass.
+    let enable_ad = config.autodiff.contains(&config::AutoDiff::Enable);
+    let stage =
+        if enable_ad { write::AutodiffStage::DuringAD } else { write::AutodiffStage::PostAD };
+
+    if enable_ad {
+        enable_autodiff_settings(&config.autodiff, module);
+    }
+
     unsafe {
-        write::llvm_optimize(
-            cgcx,
-            dcx,
-            module,
-            config,
-            opt_level,
-            opt_stage,
-            write::AutodiffStage::DuringAD,
-        )?;
+        write::llvm_optimize(cgcx, dcx, module, config, opt_level, opt_stage, stage)?;
     }
-    // FIXME(ZuseZ4): Make this more granular
-    if cfg!(llvm_enzyme) && !thin {
+
+    if cfg!(llvm_enzyme) && enable_ad {
+        let opt_stage = llvm::OptStage::FatLTO;
+        let stage = write::AutodiffStage::PostAD;
         unsafe {
-            write::llvm_optimize(
-                cgcx,
-                dcx,
-                module,
-                config,
-                opt_level,
-                llvm::OptStage::FatLTO,
-                write::AutodiffStage::PostAD,
-            )?;
+            write::llvm_optimize(cgcx, dcx, module, config, opt_level, opt_stage, stage)?;
+        }
+
+        // This is the final IR, so people should be able to inspect the optimized autodiff output.
+        if config.autodiff.contains(&config::AutoDiff::PrintModAfter) {
+            unsafe { llvm::LLVMDumpModule(module.module_llvm.llmod()) };
         }
     }
+
     debug!("lto done");
     Ok(())
 }
diff --git a/compiler/rustc_codegen_llvm/src/back/write.rs b/compiler/rustc_codegen_llvm/src/back/write.rs
index 9fa10e96068..b67890c0465 100644
--- a/compiler/rustc_codegen_llvm/src/back/write.rs
+++ b/compiler/rustc_codegen_llvm/src/back/write.rs
@@ -564,19 +564,16 @@ pub(crate) unsafe fn llvm_optimize(
     // FIXME(ZuseZ4): In a future update we could figure out how to only optimize individual functions getting
     // differentiated.
 
+    let consider_ad = cfg!(llvm_enzyme) && config.autodiff.contains(&config::AutoDiff::Enable);
+    let run_enzyme = autodiff_stage == AutodiffStage::DuringAD;
     let unroll_loops;
     let vectorize_slp;
     let vectorize_loop;
-    let run_enzyme = cfg!(llvm_enzyme) && autodiff_stage == AutodiffStage::DuringAD;
 
     // When we build rustc with enzyme/autodiff support, we want to postpone size-increasing
     // optimizations until after differentiation. Our pipeline is thus: (opt + enzyme), (full opt).
     // We therefore have two calls to llvm_optimize, if autodiff is used.
-    //
-    // FIXME(ZuseZ4): Before shipping on nightly,
-    // we should make this more granular, or at least check that the user has at least one autodiff
-    // call in their code, to justify altering the compilation pipeline.
-    if cfg!(llvm_enzyme) && autodiff_stage != AutodiffStage::PostAD {
+    if consider_ad && autodiff_stage != AutodiffStage::PostAD {
         unroll_loops = false;
         vectorize_slp = false;
         vectorize_loop = false;
@@ -706,10 +703,8 @@ pub(crate) unsafe fn optimize(
 
         // If we know that we will later run AD, then we disable vectorization and loop unrolling.
         // Otherwise we pretend AD is already done and run the normal opt pipeline (=PostAD).
-        // FIXME(ZuseZ4): Make this more granular, only set PreAD if we actually have autodiff
-        // usages, not just if we build rustc with autodiff support.
-        let autodiff_stage =
-            if cfg!(llvm_enzyme) { AutodiffStage::PreAD } else { AutodiffStage::PostAD };
+        let consider_ad = cfg!(llvm_enzyme) && config.autodiff.contains(&config::AutoDiff::Enable);
+        let autodiff_stage = if consider_ad { AutodiffStage::PreAD } else { AutodiffStage::PostAD };
         return unsafe {
             llvm_optimize(cgcx, dcx, module, config, opt_level, opt_stage, autodiff_stage)
         };
diff --git a/compiler/rustc_codegen_llvm/src/builder/autodiff.rs b/compiler/rustc_codegen_llvm/src/builder/autodiff.rs
index b2c1088e3fc..2c7899975e3 100644
--- a/compiler/rustc_codegen_llvm/src/builder/autodiff.rs
+++ b/compiler/rustc_codegen_llvm/src/builder/autodiff.rs
@@ -10,7 +10,7 @@ use crate::back::write::llvm_err;
 use crate::builder::SBuilder;
 use crate::context::SimpleCx;
 use crate::declare::declare_simple_fn;
-use crate::errors::LlvmError;
+use crate::errors::{AutoDiffWithoutEnable, LlvmError};
 use crate::llvm::AttributePlace::Function;
 use crate::llvm::{Metadata, True};
 use crate::value::Value;
@@ -46,9 +46,6 @@ fn generate_enzyme_call<'ll>(
     let output = attrs.ret_activity;
 
     // We have to pick the name depending on whether we want forward or reverse mode autodiff.
-    // FIXME(ZuseZ4): The new pass based approach should not need the {Forward/Reverse}First method anymore, since
-    // it will handle higher-order derivatives correctly automatically (in theory). Currently
-    // higher-order derivatives fail, so we should debug that before adjusting this code.
     let mut ad_name: String = match attrs.mode {
         DiffMode::Forward => "__enzyme_fwddiff",
         DiffMode::Reverse => "__enzyme_autodiff",
@@ -291,6 +288,14 @@ pub(crate) fn differentiate<'ll>(
     let diag_handler = cgcx.create_dcx();
     let cx = SimpleCx { llmod: module.module_llvm.llmod(), llcx: module.module_llvm.llcx };
 
+    // 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)
+    {
+        let dcx = cgcx.create_dcx();
+        return Err(dcx.handle().emit_almost_fatal(AutoDiffWithoutEnable));
+    }
+
     // Before dumping the module, we want all the TypeTrees to become part of the module.
     for item in diff_items.iter() {
         let name = item.source.clone();
diff --git a/compiler/rustc_codegen_llvm/src/errors.rs b/compiler/rustc_codegen_llvm/src/errors.rs
index 97f49256165..4c5a78ca74f 100644
--- a/compiler/rustc_codegen_llvm/src/errors.rs
+++ b/compiler/rustc_codegen_llvm/src/errors.rs
@@ -92,10 +92,13 @@ impl<G: EmissionGuarantee> Diagnostic<'_, G> for ParseTargetMachineConfig<'_> {
 
 #[derive(Diagnostic)]
 #[diag(codegen_llvm_autodiff_without_lto)]
-#[note]
 pub(crate) struct AutoDiffWithoutLTO;
 
 #[derive(Diagnostic)]
+#[diag(codegen_llvm_autodiff_without_enable)]
+pub(crate) struct AutoDiffWithoutEnable;
+
+#[derive(Diagnostic)]
 #[diag(codegen_llvm_lto_disallowed)]
 pub(crate) struct LtoDisallowed;
 
diff --git a/compiler/rustc_codegen_llvm/src/llvm/enzyme_ffi.rs b/compiler/rustc_codegen_llvm/src/llvm/enzyme_ffi.rs
index 39bac13a968..daa6696e963 100644
--- a/compiler/rustc_codegen_llvm/src/llvm/enzyme_ffi.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm/enzyme_ffi.rs
@@ -35,3 +35,97 @@ pub enum LLVMRustVerifierFailureAction {
     LLVMPrintMessageAction = 1,
     LLVMReturnStatusAction = 2,
 }
+
+#[cfg(llvm_enzyme)]
+pub use self::Enzyme_AD::*;
+
+#[cfg(llvm_enzyme)]
+pub mod Enzyme_AD {
+    use libc::c_void;
+    extern "C" {
+        pub fn EnzymeSetCLBool(arg1: *mut ::std::os::raw::c_void, arg2: u8);
+    }
+    extern "C" {
+        static mut EnzymePrintPerf: c_void;
+        static mut EnzymePrintActivity: c_void;
+        static mut EnzymePrintType: c_void;
+        static mut EnzymePrint: c_void;
+        static mut EnzymeStrictAliasing: c_void;
+        static mut looseTypeAnalysis: c_void;
+        static mut EnzymeInline: c_void;
+        static mut RustTypeRules: c_void;
+    }
+    pub fn set_print_perf(print: bool) {
+        unsafe {
+            EnzymeSetCLBool(std::ptr::addr_of_mut!(EnzymePrintPerf), print as u8);
+        }
+    }
+    pub fn set_print_activity(print: bool) {
+        unsafe {
+            EnzymeSetCLBool(std::ptr::addr_of_mut!(EnzymePrintActivity), print as u8);
+        }
+    }
+    pub fn set_print_type(print: bool) {
+        unsafe {
+            EnzymeSetCLBool(std::ptr::addr_of_mut!(EnzymePrintType), print as u8);
+        }
+    }
+    pub fn set_print(print: bool) {
+        unsafe {
+            EnzymeSetCLBool(std::ptr::addr_of_mut!(EnzymePrint), print as u8);
+        }
+    }
+    pub fn set_strict_aliasing(strict: bool) {
+        unsafe {
+            EnzymeSetCLBool(std::ptr::addr_of_mut!(EnzymeStrictAliasing), strict as u8);
+        }
+    }
+    pub fn set_loose_types(loose: bool) {
+        unsafe {
+            EnzymeSetCLBool(std::ptr::addr_of_mut!(looseTypeAnalysis), loose as u8);
+        }
+    }
+    pub fn set_inline(val: bool) {
+        unsafe {
+            EnzymeSetCLBool(std::ptr::addr_of_mut!(EnzymeInline), val as u8);
+        }
+    }
+    pub fn set_rust_rules(val: bool) {
+        unsafe {
+            EnzymeSetCLBool(std::ptr::addr_of_mut!(RustTypeRules), val as u8);
+        }
+    }
+}
+
+#[cfg(not(llvm_enzyme))]
+pub use self::Fallback_AD::*;
+
+#[cfg(not(llvm_enzyme))]
+pub mod Fallback_AD {
+    #![allow(unused_variables)]
+
+    pub fn set_inline(val: bool) {
+        unimplemented!()
+    }
+    pub fn set_print_perf(print: bool) {
+        unimplemented!()
+    }
+    pub fn set_print_activity(print: bool) {
+        unimplemented!()
+    }
+    pub fn set_print_type(print: bool) {
+        unimplemented!()
+    }
+    pub fn set_print(print: bool) {
+        unimplemented!()
+    }
+    pub fn set_strict_aliasing(strict: bool) {
+        unimplemented!()
+    }
+    pub fn set_loose_types(loose: bool) {
+        unimplemented!()
+    }
+    pub fn set_rust_rules(val: bool) {
+        unimplemented!()
+    }
+}