commit d2d2fb19f7ea3b192247ca2d6995e66229366cec
author Johannes Doerfert <johannes@jdoerfert.de> Thu Jan 02 17:20:47 2020 -0600
committer Johannes Doerfert <johannes@jdoerfert.de> Fri Jan 03 10:43:40 2020 -0600
tree 1e758e8dcf9812ca0f5f2884c88935faf5a6bb13
parent 6b9ee2d6cd9fc3534bb9d7e1582c57f1857e411b

[Attributor][FIX] Allow dead users of rewritten function

If we replace a function with a new one because we rewrite the
signature, dead users may still refer to the old version. With this
patch we reuse the code that deals with dead functions, which the old
versions are, to avoid problems.

llvm/lib/Transforms/IPO/Attributor.cpp

diff --git a/llvm/lib/Transforms/IPO/Attributor.cpp b/llvm/lib/Transforms/IPO/Attributor.cpp
index a8d7eb3..ef52775 100644
--- a/llvm/lib/Transforms/IPO/Attributor.cpp
+++ b/llvm/lib/Transforms/IPO/Attributor.cpp
@@ -5727,11 +5727,12 @@
     }
   }
 
+  STATS_DECL(AAIsDead, Function, "Number of dead functions deleted.");
+  BUILD_STAT_NAME(AAIsDead, Function) += ToBeDeletedFunctions.size();
+
   // Rewrite the functions as requested during manifest.
   ManifestChange = ManifestChange | rewriteFunctionSignatures();
 
-  STATS_DECL(AAIsDead, Function, "Number of dead functions deleted.");
-  BUILD_STAT_NAME(AAIsDead, Function) += ToBeDeletedFunctions.size();
   for (Function *Fn : ToBeDeletedFunctions) {
     Fn->deleteBody();
     Fn->replaceAllUsesWith(UndefValue::get(Fn->getType()));
@@ -5890,8 +5891,9 @@
     NewFn->getBasicBlockList().splice(NewFn->begin(),
                                       OldFn->getBasicBlockList());
 
-    // Set of all "call-like" instructions that invoke the old function.
-    SmallPtrSet<Instruction *, 8> OldCallSites;
+    // Set of all "call-like" instructions that invoke the old function mapped
+    // to their new replacements.
+    SmallVector<std::pair<CallBase *, CallBase *>, 8> CallSitePairs;
 
     // Callback to create a new "call-like" instruction for a given one.
     auto CallSiteReplacementCreator = [&](AbstractCallSite ACS) {
@@ -5943,7 +5945,6 @@
       }
 
       // Copy over various properties and the new attributes.
-      OldCB->replaceAllUsesWith(NewCB);
       uint64_t W;
       if (OldCB->extractProfTotalWeight(W))
         NewCB->setProfWeight(W);
@@ -5954,10 +5955,7 @@
           Ctx, OldCallAttributeList.getFnAttributes(),
           OldCallAttributeList.getRetAttributes(), NewArgOperandAttributes));
 
-      bool Inserted = OldCallSites.insert(OldCB).second;
-      assert(Inserted && "Call site was old twice!");
-      (void)Inserted;
-
+      CallSitePairs.push_back({OldCB, NewCB});
       return true;
     };
 
@@ -5984,11 +5982,15 @@
     }
 
     // Eliminate the instructions *after* we visited all of them.
-    for (Instruction *OldCallSite : OldCallSites)
-      OldCallSite->eraseFromParent();
+    for (auto &CallSitePair : CallSitePairs) {
+      CallBase &OldCB = *CallSitePair.first;
+      CallBase &NewCB = *CallSitePair.second;
+      OldCB.replaceAllUsesWith(&NewCB);
+      OldCB.eraseFromParent();
+    }
 
-    assert(OldFn->getNumUses() == 0 && "Unexpected leftover uses!");
-    OldFn->eraseFromParent();
+    ToBeDeletedFunctions.insert(OldFn);
+
     Changed = ChangeStatus::CHANGED;
   }