[PM/AA] Remove the addEscapingUse update API that won't be easy to

directly model in the new PM.

This also was an incredibly brittle and expensive update API that was
never fully utilized by all the passes that claimed to preserve AA, nor
could it reasonably have been extended to all of them. Any number of
places add uses of values. If we ever wanted to reliably instrument
this, we would want a callback hook much like we have with ValueHandles,
but doing this for every use addition seems *extremely* expensive in
terms of compile time.

The only user of this update mechanism is GlobalsModRef. The idea of
using this to keep it up to date doesn't really work anyways as its
analysis requires a symmetric analysis of two different memory
locations. It would be very hard to make updates be sufficiently
rigorous to *guarantee* symmetric analysis in this way, and it pretty
certainly isn't true today.

However, folks have been using GMR with this update for a long time and
seem to not be hitting the issues. The reported issue that the update
hook fixes isn't even a problem any more as other changes to
GetUnderlyingObject worked around it, and that issue stemmed from *many*
years ago. As a consequence, a prior patch provided a flag to control
the unsafe behavior of GMR, and this patch removes the update mechanism
that has questionable compile-time tradeoffs and is causing problems
with moving to the new pass manager. Note the lack of test updates --
not one test in tree actually requires this update, even for a contrived
case.

All of this was extensively discussed on the dev list, this patch will
just enact what that discussion decides on. I'm sending it for review in
part to show what I'm planning, and in part to show the *amazing* amount
of work this avoids. Every call to the AA here is something like three
to six indirect function calls, which in the non-LTO pipeline never do
any work! =[

Differential Revision: http://reviews.llvm.org/D11214

llvm-svn: 242605

llvm/include/llvm/Analysis/AliasAnalysis.h

@@ -521,17 +521,6 @@ public:
   ///
   virtual void deleteValue(Value *V);
 
-  /// addEscapingUse - This method should be used whenever an escaping use is
-  /// added to a pointer value.  Analysis implementations may either return
-  /// conservative responses for that value in the future, or may recompute
-  /// some or all internal state to continue providing precise responses.
-  ///
-  /// Escaping uses are considered by anything _except_ the following:
-  ///  - GEPs or bitcasts of the pointer
-  ///  - Loads through the pointer
-  ///  - Stores through (but not of) the pointer
-  virtual void addEscapingUse(Use &U);
-
   /// replaceWithNewValue - This method is the obvious combination of the two
   /// above, and it provided as a helper to simplify client code.
   ///

llvm/lib/Analysis/AliasAnalysis.cpp

@@ -71,11 +71,6 @@ void AliasAnalysis::deleteValue(Value *V) {
   AA->deleteValue(V);
 }
 
-void AliasAnalysis::addEscapingUse(Use &U) {
-  assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
-  AA->addEscapingUse(U);
-}
-
 AliasAnalysis::ModRefResult
 AliasAnalysis::getModRefInfo(Instruction *I, ImmutableCallSite Call) {
   // We may have two calls

llvm/lib/Analysis/IPA/GlobalsModRef.cpp

@@ -172,7 +172,6 @@ public:
   }
 
   void deleteValue(Value *V) override;
-  void addEscapingUse(Use &U) override;
 
   /// getAdjustedAnalysisPointer - This method is used when a pass implements
   /// an analysis interface through multiple inheritance.  If needed, it
@@ -623,13 +622,3 @@ void GlobalsModRef::deleteValue(Value *V) {
 
   AliasAnalysis::deleteValue(V);
 }
-
-void GlobalsModRef::addEscapingUse(Use &U) {
-  // For the purposes of this analysis, it is conservatively correct to treat
-  // a newly escaping value equivalently to a deleted one.  We could perhaps
-  // be more precise by processing the new use and attempting to update our
-  // saved analysis results to accommodate it.
-  deleteValue(U);
-
-  AliasAnalysis::addEscapingUse(U);
-}

llvm/lib/Analysis/NoAliasAnalysis.cpp

@@ -72,7 +72,6 @@ namespace {
     }
 
     void deleteValue(Value *V) override {}
-    void addEscapingUse(Use &U) override {}
 
     /// getAdjustedAnalysisPointer - This method is used when a pass implements
     /// an analysis interface through multiple inheritance.  If needed, it

llvm/lib/Transforms/Scalar/GVN.cpp

@@ -1301,24 +1301,7 @@ static Value *ConstructSSAForLoadSet(LoadInst *LI,
   }
 
   // Perform PHI construction.
-  Value *V = SSAUpdate.GetValueInMiddleOfBlock(LI->getParent());
-
-  // If new PHI nodes were created, notify alias analysis.
-  if (V->getType()->getScalarType()->isPointerTy()) {
-    AliasAnalysis *AA = gvn.getAliasAnalysis();
-
-    // Scan the new PHIs and inform alias analysis that we've added potentially
-    // escaping uses to any values that are operands to these PHIs.
-    for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i) {
-      PHINode *P = NewPHIs[i];
-      for (unsigned ii = 0, ee = P->getNumIncomingValues(); ii != ee; ++ii) {
-        unsigned jj = PHINode::getOperandNumForIncomingValue(ii);
-        AA->addEscapingUse(P->getOperandUse(jj));
-      }
-    }
-  }
-
-  return V;
+  return SSAUpdate.GetValueInMiddleOfBlock(LI->getParent());
 }
 
 Value *AvailableValueInBlock::MaterializeAdjustedValue(LoadInst *LI,
@@ -2581,18 +2564,8 @@ bool GVN::performScalarPRE(Instruction *CurInst) {
   addToLeaderTable(ValNo, Phi, CurrentBlock);
   Phi->setDebugLoc(CurInst->getDebugLoc());
   CurInst->replaceAllUsesWith(Phi);
-  if (Phi->getType()->getScalarType()->isPointerTy()) {
-    // Because we have added a PHI-use of the pointer value, it has now
-    // "escaped" from alias analysis' perspective.  We need to inform
-    // AA of this.
-    for (unsigned ii = 0, ee = Phi->getNumIncomingValues(); ii != ee; ++ii) {
-      unsigned jj = PHINode::getOperandNumForIncomingValue(ii);
-      VN.getAliasAnalysis()->addEscapingUse(Phi->getOperandUse(jj));
-    }
-
-    if (MD)
-      MD->invalidateCachedPointerInfo(Phi);
-  }
+  if (MD && Phi->getType()->getScalarType()->isPointerTy())
+    MD->invalidateCachedPointerInfo(Phi);
   VN.erase(CurInst);
   removeFromLeaderTable(ValNo, CurInst, CurrentBlock);
 

llvm/lib/Transforms/Scalar/MergedLoadStoreMotion.cpp

@@ -446,15 +446,8 @@ PHINode *MergedLoadStoreMotion::getPHIOperand(BasicBlock *BB, StoreInst *S0,
                             BB->begin());
     NewPN->addIncoming(Opd1, S0->getParent());
     NewPN->addIncoming(Opd2, S1->getParent());
-    if (NewPN->getType()->getScalarType()->isPointerTy()) {
-      // AA needs to be informed when a PHI-use of the pointer value is added
-      for (unsigned I = 0, E = NewPN->getNumIncomingValues(); I != E; ++I) {
-        unsigned J = PHINode::getOperandNumForIncomingValue(I);
-        AA->addEscapingUse(NewPN->getOperandUse(J));
-      }
-      if (MD)
-        MD->invalidateCachedPointerInfo(NewPN);
-    }
+    if (MD && NewPN->getType()->getScalarType()->isPointerTy())
+      MD->invalidateCachedPointerInfo(NewPN);
   }
   return NewPN;
 }