[llvm] [NFC][Cloning] Replace DIFinder usage in CloneFunctionInto with a MetadataPredicate (PR #129148)

[Artem Pianykh via llvm-commits]

https://github.com/artempyanykh updated https://github.com/llvm/llvm-project/pull/129148

>From f235ccffe433f1259700e4a1d70da35c80b45cfc Mon Sep 17 00:00:00 2001
From: Artem Pianykh <arr at fb.com>
Date: Tue, 25 Feb 2025 12:07:03 -0800
Subject: [PATCH] [NFC][Cloning] Replace DIFinder usage in CloneFunctionInto
 with a MetadataPredicate

Summary:
The new code should be functionally identical to the old one (but
faster). The reasoning is as follows.

In the old code when cloning within the module:
1. DIFinder traverses and collects *all* debug info reachable from a
   function, its instructions, and its owning compile unit.
2. Then "compile units, types, other subprograms, and lexical blocks of
   other subprograms" are saved in a set.
3. Then when we MapMetadata, we traverse the function's debug info
   _again_ and those nodes that are in the set from p.2 are identity
   mapped.

This looks equivalent to just doing step 3 with identity mapping based
on a predicate that says to identity map "compile units, types, other
subprograms, and lexical blocks of other subprograms" (same as in step
2). This is what the new code does.

Test Plan:
ninja check-all
There's a bunch of tests around cloning and all of them pass.

stack-info: PR: https://github.com/llvm/llvm-project/pull/129148, branch: users/artempyanykh/fast-coro-upstream-part2-take2/6
---
 llvm/lib/Transforms/Utils/CloneFunction.cpp | 32 ++++++++++++++++-----
 1 file changed, 25 insertions(+), 7 deletions(-)

diff --git a/llvm/lib/Transforms/Utils/CloneFunction.cpp b/llvm/lib/Transforms/Utils/CloneFunction.cpp
index 502c4898c5940..bdabe0e562fc9 100644
--- a/llvm/lib/Transforms/Utils/CloneFunction.cpp
+++ b/llvm/lib/Transforms/Utils/CloneFunction.cpp
@@ -50,6 +50,30 @@ void collectDebugInfoFromInstructions(const Function &F,
       DIFinder.processInstruction(*M, I);
   }
 }
+
+// Create a predicate that matches the metadata that should be identity mapped
+// during function cloning.
+MetadataPredicate createIdentityMDPredicate(const Function &F,
+                                            CloneFunctionChangeType Changes) {
+  if (Changes >= CloneFunctionChangeType::DifferentModule)
+    return [](const Metadata *MD) { return false; };
+
+  DISubprogram *SPClonedWithinModule = F.getSubprogram();
+  return [=](const Metadata *MD) {
+    // Avoid cloning types, compile units, and (other) subprograms.
+    if (isa<DICompileUnit>(MD) || isa<DIType>(MD))
+      return true;
+
+    if (auto *SP = dyn_cast<DISubprogram>(MD))
+      return SP != SPClonedWithinModule;
+
+    // If a subprogram isn't going to be cloned skip its lexical blocks as well.
+    if (auto *LScope = dyn_cast<DILocalScope>(MD))
+      return LScope->getSubprogram() != SPClonedWithinModule;
+
+    return false;
+  };
+}
 } // namespace
 
 /// See comments in Cloning.h.
@@ -325,13 +349,7 @@ void llvm::CloneFunctionInto(Function *NewFunc, const Function *OldFunc,
     }
   }
 
-  DISubprogram *SPClonedWithinModule =
-      CollectDebugInfoForCloning(*OldFunc, Changes, DIFinder);
-
-  MetadataPredicate IdentityMD =
-      [MDSet =
-           FindDebugInfoToIdentityMap(Changes, DIFinder, SPClonedWithinModule)](
-          const Metadata *MD) { return MDSet.contains(MD); };
+  MetadataPredicate IdentityMD = createIdentityMDPredicate(*OldFunc, Changes);
 
   // Cloning is always a Module level operation, since Metadata needs to be
   // cloned.