[PATCH] D117236: [Inliner] Don't removeDeadConstantUsers() when checking if a function is dead

[Arthur Eubanks via Phabricator via llvm-commits]

aeubanks created this revision.
Herald added subscribers: ormris, dexonsmith, hiraditya.
aeubanks requested review of this revision.
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Herald added a subscriber: llvm-commits.

If a function has many uses, this can take a good chunk of compile times.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D117236

Files:
  llvm/include/llvm/IR/Constant.h
  llvm/lib/Analysis/LazyCallGraph.cpp
  llvm/lib/IR/Constants.cpp
  llvm/lib/Transforms/IPO/Inliner.cpp


Index: llvm/lib/Transforms/IPO/Inliner.cpp
===================================================================
--- llvm/lib/Transforms/IPO/Inliner.cpp
+++ llvm/lib/Transforms/IPO/Inliner.cpp
@@ -946,10 +946,7 @@
       // discardable functions with comdats are checked later on.
       bool CalleeWasDeleted = false;
       if (Callee.isDiscardableIfUnused()) {
-        // To check this we also need to nuke any dead constant uses (perhaps
-        // made dead by this operation on other functions).
-        Callee.removeDeadConstantUsers();
-        if (Callee.use_empty() && !CG.isLibFunction(Callee)) {
+        if (Callee.hasZeroLiveUses() && !CG.isLibFunction(Callee)) {
           if (Callee.hasLocalLinkage() || !Callee.hasComdat()) {
             Calls->erase_if([&](const std::pair<CallBase *, int> &Call) {
               return Call.first->getCaller() == &Callee;
Index: llvm/lib/IR/Constants.cpp
===================================================================
--- llvm/lib/IR/Constants.cpp
+++ llvm/lib/IR/Constants.cpp
@@ -779,18 +779,22 @@
   }
 }
 
-bool Constant::hasOneLiveUse() const {
+bool Constant::hasOneLiveUse() const { return hasNLiveUses(1); }
+
+bool Constant::hasZeroLiveUses() const { return hasNLiveUses(0); }
+
+bool Constant::hasNLiveUses(unsigned N) const {
   unsigned NumUses = 0;
-  for (const Use &use : uses()) {
-    const Constant *User = dyn_cast<Constant>(use.getUser());
+  for (const Use &U : uses()) {
+    const Constant *User = dyn_cast<Constant>(U.getUser());
     if (!User || !constantIsDead(User, /* RemoveDeadUsers= */ false)) {
       ++NumUses;
 
-      if (NumUses > 1)
+      if (NumUses > N)
         return false;
     }
   }
-  return NumUses == 1;
+  return NumUses == N;
 }
 
 Constant *Constant::replaceUndefsWith(Constant *C, Constant *Replacement) {
Index: llvm/lib/Analysis/LazyCallGraph.cpp
===================================================================
--- llvm/lib/Analysis/LazyCallGraph.cpp
+++ llvm/lib/Analysis/LazyCallGraph.cpp
@@ -1503,7 +1503,7 @@
 void LazyCallGraph::removeDeadFunction(Function &F) {
   // FIXME: This is unnecessarily restrictive. We should be able to remove
   // functions which recursively call themselves.
-  assert(F.use_empty() &&
+  assert(F.hasZeroLiveUses() &&
          "This routine should only be called on trivially dead functions!");
 
   // We shouldn't remove library functions as they are never really dead while
Index: llvm/include/llvm/IR/Constant.h
===================================================================
--- llvm/include/llvm/IR/Constant.h
+++ llvm/include/llvm/IR/Constant.h
@@ -204,6 +204,12 @@
   /// Constant::removeDeadConstantUsers, but doesn't remove dead constants.
   bool hasOneLiveUse() const;
 
+  /// Return true if the constant has exactly one live use.
+  ///
+  /// This returns the same result as calling Value::use_empty after
+  /// Constant::removeDeadConstantUsers, but doesn't remove dead constants.
+  bool hasZeroLiveUses() const;
+
   const Constant *stripPointerCasts() const {
     return cast<Constant>(Value::stripPointerCasts());
   }
@@ -244,6 +250,8 @@
 
   /// Determine what potential relocations may be needed by this constant.
   PossibleRelocationsTy getRelocationInfo() const;
+
+  bool hasNLiveUses(unsigned N) const;
 };
 
 } // end namespace llvm


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