[IR] Add a helper Function::isReturnNonNull

[dtcxzyw]

The code is copied from CallBase::isReturnNonNull. It is required by the follow-up of #127979.

[llvmbot]

@llvm/pr-subscribers-llvm-ir

Author: Yingwei Zheng (dtcxzyw)

Changes

The code is copied from CallBase::isReturnNonNull. It is required by the follow-up of #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 --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();
 }

[nikic]

LGTM. Something you might want to consider though is that you could do different optimizations for both cases. In particular, for nonnull you can only look through inbounds gep, while for dereferenceable you can look through any gep. If you want to make use of that, then the helper is probably not going to be useful...

[dtcxzyw]

Interesting: https://alive2.llvm.org/ce/z/4RDBS8
Closed this PR until we need it in the future.