[PATCH] D66779: [Attributor] Introduce an API to delete stuff

[Johannes Doerfert via Phabricator via llvm-commits]

jdoerfert created this revision.
jdoerfert added reviewers: uenoku, sstefan1.
Herald added subscribers: bollu, hiraditya.
Herald added a project: LLVM.

During the fixpoint iteration, including the manifest stage, we should
not delete stuff as other abstract attributes might have a reference to
the value. Through the API this can now be done safely at the very end.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D66779

Files:
  llvm/include/llvm/Transforms/IPO/Attributor.h
  llvm/lib/Transforms/IPO/Attributor.cpp


Index: llvm/lib/Transforms/IPO/Attributor.cpp
===================================================================
--- llvm/lib/Transforms/IPO/Attributor.cpp
+++ llvm/lib/Transforms/IPO/Attributor.cpp
@@ -3767,6 +3767,26 @@
   assert(
       NumFinalAAs == AllAbstractAttributes.size() &&
       "Expected the final number of abstract attributes to remain unchanged!");
+
+  // Delete stuff at the end to avoid invalid references and a nice order.
+  LLVM_DEBUG(dbgs() << "\n[Attributor] Delete " << ToBeDeletedFunctions.size()
+                    << " functions and " << ToBeDeletedBlocks.size()
+                    << " blocks and " << ToBeDeletedInsts.size()
+                    << " instructions\n");
+  for (Instruction *I : ToBeDeletedInsts) {
+    if (I->hasNUsesOrMore(1))
+      I->replaceAllUsesWith(UndefValue::get(I->getType()));
+    I->eraseFromParent();
+  }
+  for (BasicBlock *BB : ToBeDeletedBlocks) {
+    // TODO: Check if we need to replace users (PHIs, indirect branches?)
+    BB->eraseFromParent();
+  }
+  for (Function *Fn : ToBeDeletedFunctions) {
+    Fn->replaceAllUsesWith(UndefValue::get(Fn->getType()));
+    Fn->eraseFromParent();
+  }
+
   return ManifestChange;
 }
 
Index: llvm/include/llvm/Transforms/IPO/Attributor.h
===================================================================
--- llvm/include/llvm/Transforms/IPO/Attributor.h
+++ llvm/include/llvm/Transforms/IPO/Attributor.h
@@ -722,6 +722,15 @@
   void identifyDefaultAbstractAttributes(
       Function &F, DenseSet<const char *> *Whitelist = nullptr);
 
+  /// Record that \p I is deleted after information was manifested.
+  void deleteAfterManifest(Instruction &I) { ToBeDeletedInsts.insert(&I); }
+
+  /// Record that \p BB is deleted after information was manifested.
+  void deleteAfterManifest(BasicBlock &BB) { ToBeDeletedBlocks.insert(&BB); }
+
+  /// Record that \p F is deleted after information was manifested.
+  void deleteAfterManifest(Function &F) { ToBeDeletedFunctions.insert(&F); }
+
   /// Return true if \p AA (or its context instruction) is assumed dead.
   ///
   /// If \p LivenessAA is not provided it is queried.
@@ -812,6 +821,14 @@
 
   /// The information cache that holds pre-processed (LLVM-IR) information.
   InformationCache &InfoCache;
+
+  /// Functions, blocks, and instructions we delete after manifest is done.
+  ///
+  ///{
+  SmallPtrSet<Function *, 8> ToBeDeletedFunctions;
+  SmallPtrSet<BasicBlock *, 8> ToBeDeletedBlocks;
+  SmallPtrSet<Instruction *, 8> ToBeDeletedInsts;
+  ///}
 };
 
 /// An interface to query the internal state of an abstract attribute.


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