[Attributor] Introduce an API to delete stuff

Summary:
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.

Reviewers: uenoku, sstefan1

Subscribers: hiraditya, bollu, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D66779

llvm-svn: 370014

1 files changed, 20 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/IPO/Attributor.cpp b/llvm/lib/Transforms/IPO/Attributor.cpp
index a6e8e528fd0..a2d470affc0 100644
--- a/llvm/lib/Transforms/IPO/Attributor.cpp
+++ b/llvm/lib/Transforms/IPO/Attributor.cpp
@@ -2641,6 +2641,26 @@ ChangeStatus Attributor::run() {
   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;
 }