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

[Nikita Popov via llvm-commits]

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@@ -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);
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nikic wrote:

Move this next to LLVMAddFunction.

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