[PlaceSafeopints] Extract out `callsGCLeafFunction`, NFC

Summary:
This will be used in a later change to RewriteStatepointsForGC.

Reviewers: reames, swaroop.sridhar

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D13490

llvm-svn: 249777

3 files changed, 30 insertions, 28 deletions

diff --git a/llvm/include/llvm/Transforms/Utils/Local.h b/llvm/include/llvm/Transforms/Utils/Local.h
index bdcbe7551cb..b7d67eaea3a 100644
--- a/llvm/include/llvm/Transforms/Utils/Local.h
+++ b/llvm/include/llvm/Transforms/Utils/Local.h
@@ -304,6 +304,18 @@ unsigned replaceDominatedUsesWith(Value *From, Value *To, DominatorTree &DT,
 /// the given BasicBlock. Returns the number of replacements made.
 unsigned replaceDominatedUsesWith(Value *From, Value *To, DominatorTree &DT,
                                   const BasicBlock *BB);
+
+
+/// \brief Return true if the CallSite CS calls a gc leaf function.
+///
+/// A leaf function is a function that does not safepoint the thread during its
+/// execution.  During a call or invoke to such a function, the callers stack
+/// does not have to be made parseable.
+///
+/// Most passes can and should ignore this information, and it is only used
+/// during lowering by the GC infrastructure.
+bool callsGCLeafFunction(ImmutableCallSite CS);
+
 } // End llvm namespace
 
 #endif
diff --git a/llvm/lib/Transforms/Scalar/PlaceSafepoints.cpp b/llvm/lib/Transforms/Scalar/PlaceSafepoints.cpp
index 1473e3db7c7..3552dcdfa73 100644
--- a/llvm/lib/Transforms/Scalar/PlaceSafepoints.cpp
+++ b/llvm/lib/Transforms/Scalar/PlaceSafepoints.cpp
@@ -192,10 +192,8 @@ static void
 InsertSafepointPoll(Instruction *InsertBefore,
                     std::vector<CallSite> &ParsePointsNeeded /*rval*/);
 
-static bool isGCLeafFunction(const CallSite &CS);
-
 static bool needsStatepoint(const CallSite &CS) {
-  if (isGCLeafFunction(CS))
+  if (callsGCLeafFunction(CS))
     return false;
   if (CS.isCall()) {
     CallInst *call = cast<CallInst>(CS.getInstruction());
@@ -752,31 +750,6 @@ INITIALIZE_PASS_BEGIN(PlaceSafepoints, "place-safepoints", "Place Safepoints",
 INITIALIZE_PASS_END(PlaceSafepoints, "place-safepoints", "Place Safepoints",
                     false, false)
 
-static bool isGCLeafFunction(const CallSite &CS) {
-  Instruction *inst = CS.getInstruction();
-  if (isa<IntrinsicInst>(inst)) {
-    // Most LLVM intrinsics are things which can never take a safepoint.
-    // As a result, we don't need to have the stack parsable at the
-    // callsite.  This is a highly useful optimization since intrinsic
-    // calls are fairly prevalent, particularly in debug builds.
-    return true;
-  }
-
-  // If this function is marked explicitly as a leaf call, we don't need to
-  // place a safepoint of it.  In fact, for correctness we *can't* in many
-  // cases.  Note: Indirect calls return Null for the called function,
-  // these obviously aren't runtime functions with attributes
-  // TODO: Support attributes on the call site as well.
-  const Function *F = CS.getCalledFunction();
-  bool isLeaf =
-      F &&
-      F->getFnAttribute("gc-leaf-function").getValueAsString().equals("true");
-  if (isLeaf) {
-    return true;
-  }
-  return false;
-}
-
 static void
 InsertSafepointPoll(Instruction *InsertBefore,
                     std::vector<CallSite> &ParsePointsNeeded /*rval*/) {
diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index 5be5a7df26b..de04ea506ce 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -1480,3 +1480,20 @@ unsigned llvm::replaceDominatedUsesWith(Value *From, Value *To,
   }
   return Count;
 }
+
+bool llvm::callsGCLeafFunction(ImmutableCallSite CS) {
+  if (isa<IntrinsicInst>(CS.getInstruction()))
+    // Most LLVM intrinsics are things which can never take a safepoint.
+    // As a result, we don't need to have the stack parsable at the
+    // callsite.  This is a highly useful optimization since intrinsic
+    // calls are fairly prevalent, particularly in debug builds.
+    return true;
+
+  // Check if the function is specifically marked as a gc leaf function.
+  //
+  // TODO: we should be checking the attributes on the call site as well.
+  if (const Function *F = CS.getCalledFunction())
+    return F->hasFnAttribute("gc-leaf-function");
+
+  return false;
+}