<rdar://problem/7352605>. When building schedule graph use mayAlias information to avoid chaining loads/stores of spill slots with non-aliased memory ops.

llvm-svn: 85934

1 files changed, 43 insertions, 15 deletions

diff --git a/llvm/lib/CodeGen/ScheduleDAGInstrs.cpp b/llvm/lib/CodeGen/ScheduleDAGInstrs.cpp
index a65e8a006db..6070ff6ed19 100644
--- a/llvm/lib/CodeGen/ScheduleDAGInstrs.cpp
+++ b/llvm/lib/CodeGen/ScheduleDAGInstrs.cpp
@@ -98,7 +98,9 @@ static const Value *getUnderlyingObject(const Value *V) {
 /// information and it can be tracked to a normal reference to a known
 /// object, return the Value for that object. Otherwise return null.
 static const Value *getUnderlyingObjectForInstr(const MachineInstr *MI,
-                                                const MachineFrameInfo *MFI) {
+                                                const MachineFrameInfo *MFI,
+                                                bool &MayAlias) {
+  MayAlias = true;
   if (!MI->hasOneMemOperand() ||
       !(*MI->memoperands_begin())->getValue() ||
       (*MI->memoperands_begin())->isVolatile())
@@ -110,6 +112,7 @@ static const Value *getUnderlyingObjectForInstr(const MachineInstr *MI,
 
   V = getUnderlyingObject(V);
   if (const PseudoSourceValue *PSV = dyn_cast<PseudoSourceValue>(V)) {
+    MayAlias = PSV->mayAlias(MFI);
     // For now, ignore PseudoSourceValues which may alias LLVM IR values
     // because the code that uses this function has no way to cope with
     // such aliases.
@@ -124,6 +127,23 @@ static const Value *getUnderlyingObjectForInstr(const MachineInstr *MI,
   return 0;
 }
 
+static bool mayUnderlyingObjectForInstrAlias(const MachineInstr *MI,
+                                             const MachineFrameInfo *MFI) {
+  if (!MI->hasOneMemOperand() ||
+      !(*MI->memoperands_begin())->getValue() ||
+      (*MI->memoperands_begin())->isVolatile())
+    return true;
+
+  const Value *V = (*MI->memoperands_begin())->getValue();
+  if (!V)
+    return true;
+
+  V = getUnderlyingObject(V);
+  if (const PseudoSourceValue *PSV = dyn_cast<PseudoSourceValue>(V))
+    return PSV->mayAlias(MFI);
+  return true;
+}
+
 void ScheduleDAGInstrs::StartBlock(MachineBasicBlock *BB) {
   if (MachineLoop *ML = MLI.getLoopFor(BB))
     if (BB == ML->getLoopLatch()) {
@@ -362,8 +382,9 @@ void ScheduleDAGInstrs::BuildSchedGraph(AliasAnalysis *AA) {
         // Unknown memory accesses. Assume the worst.
         ChainMMO = 0;
     } else if (TID.mayStore()) {
+      bool MayAlias = true;
       TrueMemOrderLatency = STORE_LOAD_LATENCY;
-      if (const Value *V = getUnderlyingObjectForInstr(MI, MFI)) {
+      if (const Value *V = getUnderlyingObjectForInstr(MI, MFI, MayAlias)) {
         // A store to a specific PseudoSourceValue. Add precise dependencies.
         // Handle the def in MemDefs, if there is one.
         std::map<const Value *, SUnit *>::iterator I = MemDefs.find(V);
@@ -383,22 +404,26 @@ void ScheduleDAGInstrs::BuildSchedGraph(AliasAnalysis *AA) {
                                        /*Reg=*/0, /*isNormalMemory=*/true));
           J->second.clear();
         }
-        // Add dependencies from all the PendingLoads, since without
-        // memoperands we must assume they alias anything.
-        for (unsigned k = 0, m = PendingLoads.size(); k != m; ++k)
-          PendingLoads[k]->addPred(SDep(SU, SDep::Order, TrueMemOrderLatency));
-        // Add a general dependence too, if needed.
-        if (Chain)
-          Chain->addPred(SDep(SU, SDep::Order, /*Latency=*/0));
-      } else {
+        if (MayAlias) {
+          // Add dependencies from all the PendingLoads, since without
+          // memoperands we must assume they alias anything.
+          for (unsigned k = 0, m = PendingLoads.size(); k != m; ++k)
+            PendingLoads[k]->addPred(SDep(SU, SDep::Order, TrueMemOrderLatency));
+          // Add a general dependence too, if needed.
+          if (Chain)
+            Chain->addPred(SDep(SU, SDep::Order, /*Latency=*/0));
+        }
+      } else if (MayAlias) {
         // Treat all other stores conservatively.
         goto new_chain;
       }
     } else if (TID.mayLoad()) {
+      bool MayAlias = true;
       TrueMemOrderLatency = 0;
       if (MI->isInvariantLoad(AA)) {
         // Invariant load, no chain dependencies needed!
-      } else if (const Value *V = getUnderlyingObjectForInstr(MI, MFI)) {
+      } else if (const Value *V = 
+                     getUnderlyingObjectForInstr(MI, MFI, MayAlias)) {
         // A load from a specific PseudoSourceValue. Add precise dependencies.
         std::map<const Value *, SUnit *>::iterator I = MemDefs.find(V);
         if (I != MemDefs.end())
@@ -414,16 +439,19 @@ void ScheduleDAGInstrs::BuildSchedGraph(AliasAnalysis *AA) {
         // Treat volatile loads conservatively. Note that this includes
         // cases where memoperand information is unavailable.
         goto new_chain;
-      } else {
-        // A normal load. Depend on the general chain, as well as on
+      } else if (MayAlias) {
+        // A "MayAlias" load. Depend on the general chain, as well as on
         // all stores. In the absense of MachineMemOperand information,
         // we can't even assume that the load doesn't alias well-behaved
         // memory locations.
         if (Chain)
           Chain->addPred(SDep(SU, SDep::Order, /*Latency=*/0));
         for (std::map<const Value *, SUnit *>::iterator I = MemDefs.begin(),
-             E = MemDefs.end(); I != E; ++I)
-          I->second->addPred(SDep(SU, SDep::Order, /*Latency=*/0));
+               E = MemDefs.end(); I != E; ++I) {
+          SUnit *DefSU = I->second;
+          if (mayUnderlyingObjectForInstrAlias(DefSU->getInstr(), MFI))
+            DefSU->addPred(SDep(SU, SDep::Order, /*Latency=*/0));
+        }
         PendingLoads.push_back(SU);
       }
     }