[llvm] [IR] Add a helper `Function::isReturnNonNull` (PR #128107)

[Yingwei Zheng via llvm-commits]

https://github.com/dtcxzyw created https://github.com/llvm/llvm-project/pull/128107

The code is copied from `CallBase::isReturnNonNull`. It is required by the follow-up of https://github.com/llvm/llvm-project/pull/127979.


>From b4cac6ad69dbe66bc86b7e0a9cd6eea7c62c161f Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Fri, 21 Feb 2025 09:40:09 +0800
Subject: [PATCH] [IR] Add a helper `Function::isReturnNonNull`

---
 llvm/include/llvm/IR/Function.h |  5 +++++
 llvm/lib/IR/Function.cpp        | 11 +++++++++++
 2 files changed, 16 insertions(+)

diff --git a/llvm/include/llvm/IR/Function.h b/llvm/include/llvm/IR/Function.h
index 29041688124bc..7ea8673bedad1 100644
--- a/llvm/include/llvm/IR/Function.h
+++ b/llvm/include/llvm/IR/Function.h
@@ -731,6 +731,11 @@ class LLVM_ABI Function : public GlobalObject, public ilist_node<Function> {
   /// create a Function) from the Function Src to this one.
   void copyAttributesFrom(const Function *Src);
 
+  /// Return true if the return value is known to be not null.
+  /// This may be because it has the nonnull attribute, or because at least
+  /// one byte is dereferenceable and the pointer is in addrspace(0).
+  bool isReturnNonNull() const;
+
   /// deleteBody - This method deletes the body of the function, and converts
   /// the linkage to external.
   ///
diff --git a/llvm/lib/IR/Function.cpp b/llvm/lib/IR/Function.cpp
index 5666f0a53866f..d22cf65769e26 100644
--- a/llvm/lib/IR/Function.cpp
+++ b/llvm/lib/IR/Function.cpp
@@ -873,6 +873,17 @@ void Function::copyAttributesFrom(const Function *Src) {
     setPrologueData(Src->getPrologueData());
 }
 
+bool Function::isReturnNonNull() const {
+  if (hasRetAttribute(Attribute::NonNull))
+    return true;
+
+  if (AttributeSets.getRetDereferenceableBytes() > 0 &&
+      !NullPointerIsDefined(this, getReturnType()->getPointerAddressSpace()))
+    return true;
+
+  return false;
+}
+
 MemoryEffects Function::getMemoryEffects() const {
   return getAttributes().getMemoryEffects();
 }