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

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-ir

Author: Yingwei Zheng (dtcxzyw)

<details>
<summary>Changes</summary>

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


---
Full diff: https://github.com/llvm/llvm-project/pull/128107.diff


2 Files Affected:

- (modified) llvm/include/llvm/IR/Function.h (+5) 
- (modified) llvm/lib/IR/Function.cpp (+11) 


``````````diff
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();
 }

``````````

</details>


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