1 files changed, 75 insertions, 0 deletions
diff --git a/src/llvm/pass_manager.rs b/src/llvm/pass_manager.rs
new file mode 100644
index 0000000..1551875
--- /dev/null
+++ b/src/llvm/pass_manager.rs
@@ -0,0 +1,75 @@
+use llvm_sys::{
+    core::{
+        LLVMCreateFunctionPassManagerForModule, LLVMDisposePassManager,
+        LLVMInitializeFunctionPassManager, LLVMRunFunctionPassManager,
+    },
+    prelude::LLVMPassManagerRef,
+    transforms::{
+        instcombine::LLVMAddInstructionCombiningPass,
+        scalar::{LLVMAddCFGSimplificationPass, LLVMAddNewGVNPass, LLVMAddReassociatePass},
+    },
+};
+
+use std::marker::PhantomData;
+
+use super::{FnValue, Module};
+
+/// Wrapper for a LLVM Function PassManager (legacy).
+pub struct FunctionPassManager<'llvm> {
+    fpm: LLVMPassManagerRef,
+    _ctx: PhantomData<&'llvm ()>,
+}
+
+impl<'llvm> FunctionPassManager<'llvm> {
+    /// Create a new Function PassManager with the following optimization passes
+    /// - InstructionCombiningPass
+    /// - ReassociatePass
+    /// - NewGVNPass
+    /// - CFGSimplificationPass
+    ///
+    /// The list of selected optimization passes is taken from the tutorial chapter [LLVM
+    /// Optimization Passes](https://llvm.org/docs/tutorial/MyFirstLanguageFrontend/LangImpl04.html#id3).
+    pub fn with_ctx(module: &'llvm Module) -> FunctionPassManager<'llvm> {
+        let fpm = unsafe {
+            // Borrows module reference.
+            LLVMCreateFunctionPassManagerForModule(module.module())
+        };
+        assert!(!fpm.is_null());
+
+        unsafe {
+            // Do simple "peephole" optimizations and bit-twiddling optzns.
+            LLVMAddInstructionCombiningPass(fpm);
+            // Reassociate expressions.
+            LLVMAddReassociatePass(fpm);
+            // Eliminate Common SubExpressions.
+            LLVMAddNewGVNPass(fpm);
+            // Simplify the control flow graph (deleting unreachable blocks, etc).
+            LLVMAddCFGSimplificationPass(fpm);
+
+            let fail = LLVMInitializeFunctionPassManager(fpm);
+            assert_eq!(fail, 0);
+        }
+
+        FunctionPassManager {
+            fpm,
+            _ctx: PhantomData,
+        }
+    }
+
+    /// Run the optimization passes registered with the Function PassManager on the function
+    /// referenced by `fn_value`.
+    pub fn run(&'llvm self, fn_value: FnValue<'llvm>) {
+        unsafe {
+            // Returns 1 if any of the passes modified the function, false otherwise.
+            LLVMRunFunctionPassManager(self.fpm, fn_value.value_ref());
+        }
+    }
+}
+
+impl Drop for FunctionPassManager<'_> {
+    fn drop(&mut self) {
+        unsafe {
+            LLVMDisposePassManager(self.fpm);
+        }
+    }
+}