[llvm] [nfc] Expose `canReturn` from FunctionAttrs (PR #135650)

[Mircea Trofin via llvm-commits]

https://github.com/mtrofin created https://github.com/llvm/llvm-project/pull/135650

None

>From c58b167e7b34cdf8f65704a510711183b9d85964 Mon Sep 17 00:00:00 2001
From: Mircea Trofin <mtrofin at google.com>
Date: Mon, 14 Apr 2025 09:37:14 -0700
Subject: [PATCH] [nfc] Expose `canReturn` from FunctionAttrs

---
 llvm/include/llvm/Analysis/CFG.h              |  1 +
 .../llvm/Transforms/IPO/FunctionAttrs.h       |  2 ++
 llvm/lib/Analysis/CFG.cpp                     | 34 ++++++++++++++++++
 llvm/lib/Transforms/IPO/FunctionAttrs.cpp     | 35 -------------------
 4 files changed, 37 insertions(+), 35 deletions(-)

diff --git a/llvm/include/llvm/Analysis/CFG.h b/llvm/include/llvm/Analysis/CFG.h
index 23bc10a4a9d1b..8451e88146d7c 100644
--- a/llvm/include/llvm/Analysis/CFG.h
+++ b/llvm/include/llvm/Analysis/CFG.h
@@ -174,6 +174,7 @@ bool containsIrreducibleCFG(RPOTraversalT &RPOTraversal, const LoopInfoT &LI) {
 
   return false;
 }
+bool canReturn(const Function &F);
 } // End llvm namespace
 
 #endif
diff --git a/llvm/include/llvm/Transforms/IPO/FunctionAttrs.h b/llvm/include/llvm/Transforms/IPO/FunctionAttrs.h
index 6a21ff616d506..3a2c09afbebd3 100644
--- a/llvm/include/llvm/Transforms/IPO/FunctionAttrs.h
+++ b/llvm/include/llvm/Transforms/IPO/FunctionAttrs.h
@@ -30,6 +30,8 @@ class Module;
 /// Returns the memory access properties of this copy of the function.
 MemoryEffects computeFunctionBodyMemoryAccess(Function &F, AAResults &AAR);
 
+bool canReturn(const Function &F);
+
 /// Propagate function attributes for function summaries along the index's
 /// callgraph during thinlink
 bool thinLTOPropagateFunctionAttrs(
diff --git a/llvm/lib/Analysis/CFG.cpp b/llvm/lib/Analysis/CFG.cpp
index 841b835052380..8ced4a901557d 100644
--- a/llvm/lib/Analysis/CFG.cpp
+++ b/llvm/lib/Analysis/CFG.cpp
@@ -322,3 +322,37 @@ bool llvm::isPotentiallyReachable(
   return isPotentiallyReachable(
       A->getParent(), B->getParent(), ExclusionSet, DT, LI);
 }
+
+static bool instructionDoesNotReturn(const Instruction &I) {
+  if (auto *CB = dyn_cast<CallBase>(&I))
+    return CB->hasFnAttr(Attribute::NoReturn);
+  return false;
+}
+
+// A basic block can only return if it terminates with a ReturnInst and does not
+// contain calls to noreturn functions.
+static bool basicBlockCanReturn(const BasicBlock &BB) {
+  if (!isa<ReturnInst>(BB.getTerminator()))
+    return false;
+  return none_of(BB, instructionDoesNotReturn);
+}
+
+// FIXME: this doesn't handle recursion.
+bool llvm::canReturn(const Function &F) {
+  SmallVector<const BasicBlock *, 16> Worklist;
+  SmallPtrSet<const BasicBlock *, 16> Visited;
+
+  Visited.insert(&F.front());
+  Worklist.push_back(&F.front());
+
+  do {
+    const BasicBlock *BB = Worklist.pop_back_val();
+    if (basicBlockCanReturn(*BB))
+      return true;
+    for (const BasicBlock *Succ : successors(BB))
+      if (Visited.insert(Succ).second)
+        Worklist.push_back(Succ);
+  } while (!Worklist.empty());
+
+  return false;
+}
diff --git a/llvm/lib/Transforms/IPO/FunctionAttrs.cpp b/llvm/lib/Transforms/IPO/FunctionAttrs.cpp
index ef7989507c89f..bbfed2ac2c090 100644
--- a/llvm/lib/Transforms/IPO/FunctionAttrs.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionAttrs.cpp
@@ -2090,41 +2090,6 @@ static void addNoRecurseAttrs(const SCCNodeSet &SCCNodes,
   Changed.insert(F);
 }
 
-static bool instructionDoesNotReturn(Instruction &I) {
-  if (auto *CB = dyn_cast<CallBase>(&I))
-    return CB->hasFnAttr(Attribute::NoReturn);
-  return false;
-}
-
-// A basic block can only return if it terminates with a ReturnInst and does not
-// contain calls to noreturn functions.
-static bool basicBlockCanReturn(BasicBlock &BB) {
-  if (!isa<ReturnInst>(BB.getTerminator()))
-    return false;
-  return none_of(BB, instructionDoesNotReturn);
-}
-
-// FIXME: this doesn't handle recursion.
-static bool canReturn(Function &F) {
-  SmallVector<BasicBlock *, 16> Worklist;
-  SmallPtrSet<BasicBlock *, 16> Visited;
-
-  Visited.insert(&F.front());
-  Worklist.push_back(&F.front());
-
-  do {
-    BasicBlock *BB = Worklist.pop_back_val();
-    if (basicBlockCanReturn(*BB))
-      return true;
-    for (BasicBlock *Succ : successors(BB))
-      if (Visited.insert(Succ).second)
-        Worklist.push_back(Succ);
-  } while (!Worklist.empty());
-
-  return false;
-}
-
-
 // Set the noreturn function attribute if possible.
 static void addNoReturnAttrs(const SCCNodeSet &SCCNodes,
                              SmallSet<Function *, 8> &Changed) {