commit 54ec9b54f6bb7d580447570fb91451f663113d35
author Johannes Doerfert <johannes@jdoerfert.de> Mon Mar 16 20:23:27 2020 -0500
committer Johannes Doerfert <johannes@jdoerfert.de> Mon Mar 23 10:45:24 2020 -0500
tree 23e7437abe809969879d120236222a58c348cbe7
parent 0995001ce5732b6338b2679924e419b4ed8e30f2

[Attributor] Unify handling of must-tail calls

We special cased must-tail calls all over the place because they cannot
be modified as other calls can be. However, we already centralized the
modification API so we can centralize the handling as well. This
simplifies the code and allows to remove must-tail calls completely.

llvm/lib/Transforms/IPO/Attributor.cpp

diff --git a/llvm/lib/Transforms/IPO/Attributor.cpp b/llvm/lib/Transforms/IPO/Attributor.cpp
index 231b42d..fb860bd 100644
--- a/llvm/lib/Transforms/IPO/Attributor.cpp
+++ b/llvm/lib/Transforms/IPO/Attributor.cpp
@@ -1317,7 +1317,7 @@
 
   // Callback to replace the uses of CB with the constant C.
   auto ReplaceCallSiteUsersWith = [&A](CallBase &CB, Constant &C) {
-    if (CB.getNumUses() == 0 || CB.isMustTailCall())
+    if (CB.getNumUses() == 0)
       return ChangeStatus::UNCHANGED;
     if (A.changeValueAfterManifest(CB, C))
       return ChangeStatus::CHANGED;
@@ -3207,14 +3207,6 @@
     return Changed;
   }
 
-  /// See AbstractAttribute::manifest(...).
-  ChangeStatus manifest(Attributor &A) override {
-    if (auto *CI = dyn_cast<CallInst>(&getAssociatedValue()))
-      if (CI->isMustTailCall())
-        return ChangeStatus::UNCHANGED;
-    return AAIsDeadFloating::manifest(A);
-  }
-
   /// See AbstractAttribute::trackStatistics()
   void trackStatistics() const override {
     if (IsAssumedSideEffectFree)
@@ -3264,9 +3256,6 @@
     UndefValue &UV = *UndefValue::get(getAssociatedFunction()->getReturnType());
     auto RetInstPred = [&](Instruction &I) {
       ReturnInst &RI = cast<ReturnInst>(I);
-      if (auto *CI = dyn_cast<CallInst>(RI.getReturnValue()))
-        if (CI->isMustTailCall())
-          return true;
       if (!isa<UndefValue>(RI.getReturnValue()))
         AnyChange |= A.changeUseAfterManifest(RI.getOperandUse(0), UV);
       return true;
@@ -4855,9 +4844,6 @@
             // We can replace the AssociatedValue with the constant.
             if (&V == C || V.getType() != C->getType() || isa<UndefValue>(V))
               return true;
-            if (auto *CI = dyn_cast<CallInst>(&V))
-              if (CI->isMustTailCall())
-                return true;
 
             for (ReturnInst *RI : RetInsts) {
               if (RI->getFunction() != getAnchorScope())
@@ -4965,9 +4951,6 @@
 
   /// See AbstractAttribute::manifest(...).
   ChangeStatus manifest(Attributor &A) override {
-    if (auto *CI = dyn_cast<CallInst>(&getAssociatedValue()))
-      if (CI->isMustTailCall())
-        return ChangeStatus::UNCHANGED;
     return AAValueSimplifyImpl::manifest(A);
   }
 
@@ -7879,6 +7862,14 @@
       Use *U = It.first;
       Value *NewV = It.second;
       Value *OldV = U->get();
+
+      // Do not replace uses in returns if the value is a must-tail call we will
+      // not delete.
+      if (isa<ReturnInst>(U->getUser()))
+        if (auto *CI = dyn_cast<CallInst>(OldV->stripPointerCasts()))
+          if (CI->isMustTailCall() && !ToBeDeletedInsts.count(CI))
+            continue;
+
       LLVM_DEBUG(dbgs() << "Use " << *NewV << " in " << *U->getUser()
                         << " instead of " << *OldV << "\n");
       U->set(NewV);