[llvm] [LLVM-C] Upstream `LLVMGetOrInsertFunction` from rustc (PR #162235)

[via llvm-commits]

https://github.com/AMS21 created https://github.com/llvm/llvm-project/pull/162235

[upstream reference](https://github.com/rust-lang/rust/blob/d773bd07d63a74adcf25ea5f4aae986be94cac5e/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp#L203)

>From 59cc9ec8a834da42db8e6755fd0be01fbebe03cb Mon Sep 17 00:00:00 2001
From: AMS21 <ams21.github at gmail.com>
Date: Tue, 7 Oct 2025 09:19:57 +0200
Subject: [PATCH] [LLVM-C] Upstream `LLVMGetOrInsertFunction` from rustc

---
 llvm/include/llvm-c/Core.h | 16 ++++++++++++++++
 llvm/lib/IR/Core.cpp       |  8 ++++++++
 2 files changed, 24 insertions(+)

diff --git a/llvm/include/llvm-c/Core.h b/llvm/include/llvm-c/Core.h
index d02cf984167c9..fdd0d1df2a25f 100644
--- a/llvm/include/llvm-c/Core.h
+++ b/llvm/include/llvm-c/Core.h
@@ -2988,6 +2988,22 @@ LLVM_C_ABI char *LLVMIntrinsicCopyOverloadedName2(LLVMModuleRef Mod,
  */
 LLVM_C_ABI LLVMBool LLVMIntrinsicIsOverloaded(unsigned ID);
 
+/**
+ * Obtain or insert a function into a module.
+ *
+ * If a function with the specified name already exists in the module, it
+ * is returned. Otherwise, a new function is created in the module with the
+ * specified name and type and is returned.
+ *
+ * The returned value corresponds to a llvm::Function instance.
+ *
+ * @see llvm::Module::getOrInsertFunction()
+ */
+LLVM_C_ABI LLVMValueRef LLVMGetOrInsertFunction(LLVMModuleRef M,
+                                                const char *Name,
+                                                size_t NameLen,
+                                                LLVMTypeRef FunctionTy);
+
 /**
  * Obtain the calling function of a function.
  *
diff --git a/llvm/lib/IR/Core.cpp b/llvm/lib/IR/Core.cpp
index df0c85b87ba60..abd06f4724fcd 100644
--- a/llvm/lib/IR/Core.cpp
+++ b/llvm/lib/IR/Core.cpp
@@ -2523,6 +2523,14 @@ LLVMBool LLVMIntrinsicIsOverloaded(unsigned ID) {
   return llvm::Intrinsic::isOverloaded(IID);
 }
 
+LLVMValueRef LLVMGetOrInsertFunction(LLVMModuleRef M, const char *Name,
+                                     size_t NameLen, LLVMTypeRef FunctionTy) {
+  return wrap(unwrap(M)
+                  ->getOrInsertFunction(StringRef(Name, NameLen),
+                                        unwrap<FunctionType>(FunctionTy))
+                  .getCallee());
+}
+
 unsigned LLVMGetFunctionCallConv(LLVMValueRef Fn) {
   return unwrap<Function>(Fn)->getCallingConv();
 }