[IR] Add argument to Function::deleteBody to preserve metadata

[jasilvanus]

Function::deleteBody deletes all function metadata, which is undesirable in some cases.

This patch adds a boolean argument PreserveMetadata to control that. The new argument defaults to false, preserving the old behavior.

[llvmbot]

@llvm/pr-subscribers-llvm-ir

Author: Jannik Silvanus (jasilvanus)

Changes

Function::deleteBody deletes all function metadata, which is undesirable in some cases.

This patch adds a boolean argument PreserveMetadata to control that. The new argument defaults to false, preserving the old behavior.

---

Full diff: https://github.com/llvm/llvm-project/pull/164960.diff

2 Files Affected:

• (modified) llvm/include/llvm/IR/Function.h (+4-4)
• (modified) llvm/lib/IR/Function.cpp (+3-2)

diff --git a/llvm/include/llvm/IR/Function.h b/llvm/include/llvm/IR/Function.h
index d3497716ca844..02232f6dc2f62 100644
--- a/llvm/include/llvm/IR/Function.h
+++ b/llvm/include/llvm/IR/Function.h
@@ -144,7 +144,7 @@ class LLVM_ABI Function : public GlobalObject, public ilist_node<Function> {
 
   void clearArguments();
 
-  void deleteBodyImpl(bool ShouldDrop);
+  void deleteBodyImpl(bool ShouldDrop, bool PreserveMetadata);
 
   /// Function ctor - If the (optional) Module argument is specified, the
   /// function is automatically inserted into the end of the function list for
@@ -727,8 +727,8 @@ class LLVM_ABI Function : public GlobalObject, public ilist_node<Function> {
   /// deleteBody - This method deletes the body of the function, and converts
   /// the linkage to external.
   ///
-  void deleteBody() {
-    deleteBodyImpl(/*ShouldDrop=*/false);
+  void deleteBody(bool PreserveMetadata = false) {
+    deleteBodyImpl(/*ShouldDrop=*/false, PreserveMetadata);
     setLinkage(ExternalLinkage);
   }
 
@@ -982,7 +982,7 @@ class LLVM_ABI Function : public GlobalObject, public ilist_node<Function> {
   /// including any contained basic blocks.
   ///
   void dropAllReferences() {
-    deleteBodyImpl(/*ShouldDrop=*/true);
+    deleteBodyImpl(/*ShouldDrop=*/true, /*PreserveMetadata=*/false);
   }
 
   /// hasAddressTaken - returns true if there are any uses of this function
diff --git a/llvm/lib/IR/Function.cpp b/llvm/lib/IR/Function.cpp
index fc067459dcba3..d50a711b83fa9 100644
--- a/llvm/lib/IR/Function.cpp
+++ b/llvm/lib/IR/Function.cpp
@@ -600,7 +600,7 @@ void Function::stealArgumentListFrom(Function &Src) {
   Src.setValueSubclassData(Src.getSubclassDataFromValue() | (1 << 0));
 }
 
-void Function::deleteBodyImpl(bool ShouldDrop) {
+void Function::deleteBodyImpl(bool ShouldDrop, bool PreserveMetadata) {
   setIsMaterializable(false);
 
   for (BasicBlock &BB : *this)
@@ -627,7 +627,8 @@ void Function::deleteBodyImpl(bool ShouldDrop) {
   }
 
   // Metadata is stored in a side-table.
-  clearMetadata();
+  if (!PreserveMetadata)
+    clearMetadata();
 }
 
 void Function::addAttributeAtIndex(unsigned i, Attribute Attr) {

[jasilvanus]

I realized Function::deleteBody also changes linkage, which my use case also does not want, instead of adding more options to Function::deleteBody I ended up just manually deleting the BBs, no longer needing this PR.

However, I'm not sure that behavior of changing a lot more than just deleting the body is what we want by default...