Add "unknown" results for memdep, which mean "I don't know whether a dependence for the given instruction exists in the given block". This cleans up all the existing hacks in memdep which represent this concept by returning clobber with various unrelated instructions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@133031 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 37 insertions, 32 deletions

diff --git a/lib/Analysis/MemDepPrinter.cpp b/lib/Analysis/MemDepPrinter.cpp
index 64d215c37c..2283db0bc4 100644
--- a/lib/Analysis/MemDepPrinter.cpp
+++ b/lib/Analysis/MemDepPrinter.cpp
@@ -79,8 +79,8 @@ bool MemDepPrinter::runOnFunction(Function &F) {
 
     MemDepResult Res = MDA.getDependency(Inst);
     if (!Res.isNonLocal()) {
-      assert(Res.isClobber() != Res.isDef() &&
-             "Local dep should be def or clobber!");
+      assert((Res.isUnknown() || Res.isClobber() || Res.isDef()) &&
+              "Local dep should be unknown, def or clobber!");
       Deps[Inst].insert(std::make_pair(InstAndClobberFlag(Res.getInst(),
                                                           Res.isClobber()),
                                        static_cast<BasicBlock *>(0)));
@@ -92,8 +92,9 @@ bool MemDepPrinter::runOnFunction(Function &F) {
       for (MemoryDependenceAnalysis::NonLocalDepInfo::const_iterator
            I = NLDI.begin(), E = NLDI.end(); I != E; ++I) {
         const MemDepResult &Res = I->getResult();
-        assert(Res.isClobber() != Res.isDef() &&
-               "Resolved non-local call dep should be def or clobber!");
+        assert((Res.isUnknown() || Res.isClobber() || Res.isDef()) &&
+                "Resolved non-local call dep should be unknown, def or "
+                "clobber!");
         InstDeps.insert(std::make_pair(InstAndClobberFlag(Res.getInst(),
                                                           Res.isClobber()),
                                        I->getBB()));
@@ -148,16 +149,24 @@ void MemDepPrinter::print(raw_ostream &OS, const Module *M) const {
       bool isClobber = I->first.getInt();
       const BasicBlock *DepBB = I->second;
 
-      OS << "    " << (isClobber ? "Clobber" : "    Def");
+      OS << "    ";
+      if (!DepInst)
+        OS << "Unknown";
+      else if (isClobber)
+        OS << "Clobber";
+      else
+        OS << "    Def";
       if (DepBB) {
         OS << " in block ";
         WriteAsOperand(OS, DepBB, /*PrintType=*/false, M);
       }
-      OS << " from: ";
-      if (DepInst == Inst)
-        OS << "<unspecified>";
-      else
-        DepInst->print(OS);
+      if (DepInst) {
+        OS << " from: ";
+        if (DepInst == Inst)
+          OS << "<unspecified>";
+        else
+          DepInst->print(OS);
+      }
       OS << "\n";
     }
 
diff --git a/lib/Analysis/MemoryDependenceAnalysis.cpp b/lib/Analysis/MemoryDependenceAnalysis.cpp
index 5f640c01d2..ed638ff1c0 100644
--- a/lib/Analysis/MemoryDependenceAnalysis.cpp
+++ b/lib/Analysis/MemoryDependenceAnalysis.cpp
@@ -215,11 +215,11 @@ getCallSiteDependencyFrom(CallSite CS, bool isReadOnlyCall,
     }
   }
   
-  // No dependence found.  If this is the entry block of the function, it is a
-  // clobber, otherwise it is non-local.
+  // No dependence found.  If this is the entry block of the function, it is
+  // unknown, otherwise it is non-local.
   if (BB != &BB->getParent()->getEntryBlock())
     return MemDepResult::getNonLocal();
-  return MemDepResult::getClobber(ScanIt);
+  return MemDepResult::getUnknown();
 }
 
 /// isLoadLoadClobberIfExtendedToFullWidth - Return true if LI is a load that
@@ -458,11 +458,11 @@ getPointerDependencyFrom(const AliasAnalysis::Location &MemLoc, bool isLoad,
     }
   }
   
-  // No dependence found.  If this is the entry block of the function, it is a
-  // clobber, otherwise it is non-local.
+  // No dependence found.  If this is the entry block of the function, it is
+  // unknown, otherwise it is non-local.
   if (BB != &BB->getParent()->getEntryBlock())
     return MemDepResult::getNonLocal();
-  return MemDepResult::getClobber(ScanIt);
+  return MemDepResult::getUnknown();
 }
 
 /// getDependency - Return the instruction on which a memory operation
@@ -490,12 +490,12 @@ MemDepResult MemoryDependenceAnalysis::getDependency(Instruction *QueryInst) {
   
   // Do the scan.
   if (BasicBlock::iterator(QueryInst) == QueryParent->begin()) {
-    // No dependence found.  If this is the entry block of the function, it is a
-    // clobber, otherwise it is non-local.
+    // No dependence found.  If this is the entry block of the function, it is
+    // unknown, otherwise it is non-local.
     if (QueryParent != &QueryParent->getParent()->getEntryBlock())
       LocalCache = MemDepResult::getNonLocal();
     else
-      LocalCache = MemDepResult::getClobber(QueryInst);
+      LocalCache = MemDepResult::getUnknown();
   } else {
     AliasAnalysis::Location MemLoc;
     AliasAnalysis::ModRefResult MR = GetLocation(QueryInst, MemLoc, AA);
@@ -514,7 +514,7 @@ MemDepResult MemoryDependenceAnalysis::getDependency(Instruction *QueryInst) {
                                              QueryParent);
     } else
       // Non-memory instruction.
-      LocalCache = MemDepResult::getClobber(--BasicBlock::iterator(ScanPos));
+      LocalCache = MemDepResult::getUnknown();
   }
   
   // Remember the result!
@@ -648,10 +648,10 @@ MemoryDependenceAnalysis::getNonLocalCallDependency(CallSite QueryCS) {
       Dep = getCallSiteDependencyFrom(QueryCS, isReadonlyCall,ScanPos, DirtyBB);
     } else if (DirtyBB != &DirtyBB->getParent()->getEntryBlock()) {
       // No dependence found.  If this is the entry block of the function, it is
-      // a clobber, otherwise it is non-local.
+      // a clobber, otherwise it is unknown.
       Dep = MemDepResult::getNonLocal();
     } else {
-      Dep = MemDepResult::getClobber(ScanPos);
+      Dep = MemDepResult::getUnknown();
     }
     
     // If we had a dirty entry for the block, update it.  Otherwise, just add
@@ -707,7 +707,7 @@ getNonLocalPointerDependency(const AliasAnalysis::Location &Loc, bool isLoad,
     return;
   Result.clear();
   Result.push_back(NonLocalDepResult(FromBB,
-                                     MemDepResult::getClobber(FromBB->begin()),
+                                     MemDepResult::getUnknown(),
                                      const_cast<Value *>(Loc.Ptr)));
 }
 
@@ -769,7 +769,7 @@ GetNonLocalInfoForBlock(const AliasAnalysis::Location &Loc,
   // If the block has a dependency (i.e. it isn't completely transparent to
   // the value), remember the reverse association because we just added it
   // to Cache!
-  if (Dep.isNonLocal())
+  if (Dep.isNonLocal() || Dep.isUnknown())
     return Dep;
   
   // Keep the ReverseNonLocalPtrDeps map up to date so we can efficiently
@@ -1091,16 +1091,14 @@ getNonLocalPointerDepFromBB(const PHITransAddr &Pointer,
 
       // If getNonLocalPointerDepFromBB fails here, that means the cached
       // result conflicted with the Visited list; we have to conservatively
-      // assume a clobber, but this also does not block PRE of the load.
+      // assume it is unknown, but this also does not block PRE of the load.
       if (!CanTranslate ||
           getNonLocalPointerDepFromBB(PredPointer,
                                       Loc.getWithNewPtr(PredPtrVal),
                                       isLoad, Pred,
                                       Result, Visited)) {
         // Add the entry to the Result list.
-        NonLocalDepResult Entry(Pred,
-                                MemDepResult::getClobber(Pred->getTerminator()),
-                                PredPtrVal);
+        NonLocalDepResult Entry(Pred, MemDepResult::getUnknown(), PredPtrVal);
         Result.push_back(Entry);
 
         // Since we had a phi translation failure, the cache for CacheKey won't
@@ -1145,8 +1143,7 @@ getNonLocalPointerDepFromBB(const PHITransAddr &Pointer,
     // results from the set".  Clear out the indicator for this.
     CacheInfo->Pair = BBSkipFirstBlockPair();
     
-    // If *nothing* works, mark the pointer as being clobbered by the first
-    // instruction in this block.
+    // If *nothing* works, mark the pointer as unknown.
     //
     // If this is the magic first block, return this as a clobber of the whole
     // incoming value.  Since we can't phi translate to one of the predecessors,
@@ -1161,8 +1158,7 @@ getNonLocalPointerDepFromBB(const PHITransAddr &Pointer,
       
       assert(I->getResult().isNonLocal() &&
              "Should only be here with transparent block");
-      I->setResult(MemDepResult::getClobber(BB->getTerminator()));
-      ReverseNonLocalPtrDeps[BB->getTerminator()].insert(CacheKey);
+      I->setResult(MemDepResult::getUnknown());
       Result.push_back(NonLocalDepResult(I->getBB(), I->getResult(),
                                          Pointer.getAddr()));
       break;