From: David Goodwin <david_goodwin@apple.com>
Date: Mon, 2 Nov 2009 17:06:28 +0000 (+0000)
Subject: Chain dependencies used to enforce memory order should have latency of 0 (except... 
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=7c9b1ac5073a4988a9ed39aed6cd5a22e6a1c24f;p=oota-llvm.git

Chain dependencies used to enforce memory order should have latency of 0 (except for true dependency of Store followed by aliased Load... we estimate that case with a single cycle of latency assuming the hardware will bypass)



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@85807 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/CodeGen/ScheduleDAGInstrs.cpp b/lib/CodeGen/ScheduleDAGInstrs.cpp
index 880782e2817..a65e8a006db 100644
--- a/lib/CodeGen/ScheduleDAGInstrs.cpp
+++ b/lib/CodeGen/ScheduleDAGInstrs.cpp
@@ -317,29 +317,35 @@ void ScheduleDAGInstrs::BuildSchedGraph(AliasAnalysis *AA) {
     }
 
     // Add chain dependencies.
+    // Chain dependencies used to enforce memory order should have
+    // latency of 0 (except for true dependency of Store followed by
+    // aliased Load... we estimate that with a single cycle of latency
+    // assuming the hardware will bypass)
     // Note that isStoreToStackSlot and isLoadFromStackSLot are not usable
     // after stack slots are lowered to actual addresses.
     // TODO: Use an AliasAnalysis and do real alias-analysis queries, and
     // produce more precise dependence information.
+#define STORE_LOAD_LATENCY 1
+    unsigned TrueMemOrderLatency = 0;
     if (TID.isCall() || TID.hasUnmodeledSideEffects()) {
     new_chain:
       // This is the conservative case. Add dependencies on all memory
       // references.
       if (Chain)
-        Chain->addPred(SDep(SU, SDep::Order, SU->Latency));
+        Chain->addPred(SDep(SU, SDep::Order, /*Latency=*/0));
       Chain = SU;
       for (unsigned k = 0, m = PendingLoads.size(); k != m; ++k)
-        PendingLoads[k]->addPred(SDep(SU, SDep::Order, SU->Latency));
+        PendingLoads[k]->addPred(SDep(SU, SDep::Order, TrueMemOrderLatency));
       PendingLoads.clear();
       for (std::map<const Value *, SUnit *>::iterator I = MemDefs.begin(),
            E = MemDefs.end(); I != E; ++I) {
-        I->second->addPred(SDep(SU, SDep::Order, SU->Latency));
+        I->second->addPred(SDep(SU, SDep::Order, /*Latency=*/0));
         I->second = SU;
       }
       for (std::map<const Value *, std::vector<SUnit *> >::iterator I =
            MemUses.begin(), E = MemUses.end(); I != E; ++I) {
         for (unsigned i = 0, e = I->second.size(); i != e; ++i)
-          I->second[i]->addPred(SDep(SU, SDep::Order, SU->Latency));
+          I->second[i]->addPred(SDep(SU, SDep::Order, TrueMemOrderLatency));
         I->second.clear();
       }
       // See if it is known to just have a single memory reference.
@@ -356,12 +362,13 @@ void ScheduleDAGInstrs::BuildSchedGraph(AliasAnalysis *AA) {
         // Unknown memory accesses. Assume the worst.
         ChainMMO = 0;
     } else if (TID.mayStore()) {
+      TrueMemOrderLatency = STORE_LOAD_LATENCY;
       if (const Value *V = getUnderlyingObjectForInstr(MI, MFI)) {
         // 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);
         if (I != MemDefs.end()) {
-          I->second->addPred(SDep(SU, SDep::Order, SU->Latency, /*Reg=*/0,
+          I->second->addPred(SDep(SU, SDep::Order, /*Latency=*/0, /*Reg=*/0,
                                   /*isNormalMemory=*/true));
           I->second = SU;
         } else {
@@ -372,35 +379,37 @@ void ScheduleDAGInstrs::BuildSchedGraph(AliasAnalysis *AA) {
           MemUses.find(V);
         if (J != MemUses.end()) {
           for (unsigned i = 0, e = J->second.size(); i != e; ++i)
-            J->second[i]->addPred(SDep(SU, SDep::Order, SU->Latency, /*Reg=*/0,
-                                       /*isNormalMemory=*/true));
+            J->second[i]->addPred(SDep(SU, SDep::Order, TrueMemOrderLatency,
+                                       /*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, SU->Latency));
+          PendingLoads[k]->addPred(SDep(SU, SDep::Order, TrueMemOrderLatency));
         // Add a general dependence too, if needed.
         if (Chain)
-          Chain->addPred(SDep(SU, SDep::Order, SU->Latency));
-      } else
+          Chain->addPred(SDep(SU, SDep::Order, /*Latency=*/0));
+      } else {
         // Treat all other stores conservatively.
         goto new_chain;
+      }
     } else if (TID.mayLoad()) {
+      TrueMemOrderLatency = 0;
       if (MI->isInvariantLoad(AA)) {
         // Invariant load, no chain dependencies needed!
       } else if (const Value *V = getUnderlyingObjectForInstr(MI, MFI)) {
         // A load from a specific PseudoSourceValue. Add precise dependencies.
         std::map<const Value *, SUnit *>::iterator I = MemDefs.find(V);
         if (I != MemDefs.end())
-          I->second->addPred(SDep(SU, SDep::Order, SU->Latency, /*Reg=*/0,
+          I->second->addPred(SDep(SU, SDep::Order, /*Latency=*/0, /*Reg=*/0,
                                   /*isNormalMemory=*/true));
         MemUses[V].push_back(SU);
 
         // Add a general dependence too, if needed.
         if (Chain && (!ChainMMO ||
                       (ChainMMO->isStore() || ChainMMO->isVolatile())))
-          Chain->addPred(SDep(SU, SDep::Order, SU->Latency));
+          Chain->addPred(SDep(SU, SDep::Order, /*Latency=*/0));
       } else if (MI->hasVolatileMemoryRef()) {
         // Treat volatile loads conservatively. Note that this includes
         // cases where memoperand information is unavailable.
@@ -411,10 +420,10 @@ void ScheduleDAGInstrs::BuildSchedGraph(AliasAnalysis *AA) {
         // we can't even assume that the load doesn't alias well-behaved
         // memory locations.
         if (Chain)
-          Chain->addPred(SDep(SU, SDep::Order, SU->Latency));
+          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, SU->Latency));
+          I->second->addPred(SDep(SU, SDep::Order, /*Latency=*/0));
         PendingLoads.push_back(SU);
       }
     }