New method SDep::isNormalMemoryOrBarrier() in ScheduleDAGInstrs.cpp.

Used to iterate over previously added memory dependencies in
adjustChainDeps() and iterateChainSucc().

SDep::isCtrl() was previously used in these places, that also gave
anti and output edges. The code may be worse if these are followed,
because MisNeedChainEdge() will conservatively return true since a
non-memory instruction has no memory operands, and a false chain dep
will be added. It is also unnecessary since all memory accesses of
interest will be reached by memory dependencies, and there is a budget
limit for the number of edges traversed.

This problem was found on an out-of-tree target with enabled alias
analysis. No test case for an in-tree target has been found.

Reviewed by Hal Finkel.

llvm-svn: 225351

include/llvm/CodeGen/ScheduleDAG.h

@@ -190,6 +190,12 @@ namespace llvm {
       return getKind() == Order && Contents.OrdKind == Barrier;
     }
 
+    /// isNormalMemoryOrBarrier - Test if this is could be any kind of memory
+    /// dependence.
+    bool isNormalMemoryOrBarrier() const {
+      return (isNormalMemory() || isBarrier());
+    }
+
     /// isMustAlias - Test if this is an Order dependence that is marked
     /// as "must alias", meaning that the SUnits at either end of the edge
     /// have a memory dependence on a known memory location.

lib/CodeGen/ScheduleDAGInstrs.cpp

@@ -614,10 +614,10 @@ iterateChainSucc(AliasAnalysis *AA, const MachineFrameInfo *MFI,
   }
   // Track current depth.
   (*Depth)++;
-  // Iterate over chain dependencies only.
+  // Iterate over memory dependencies only.
   for (SUnit::const_succ_iterator I = SUb->Succs.begin(), E = SUb->Succs.end();
        I != E; ++I)
-    if (I->isCtrl())
+    if (I->isNormalMemoryOrBarrier())
       iterateChainSucc (AA, MFI, SUa, I->getSUnit(), ExitSU, Depth, Visited);
   return *Depth;
 }
@@ -644,11 +644,12 @@ static void adjustChainDeps(AliasAnalysis *AA, const MachineFrameInfo *MFI,
       Dep.setLatency(((*I)->getInstr()->mayLoad()) ? LatencyToLoad : 0);
       (*I)->addPred(Dep);
     }
-    // Now go through all the chain successors and iterate from them.
-    // Keep track of visited nodes.
+
+    // Iterate recursively over all previously added memory chain
+    // successors. Keep track of visited nodes.
     for (SUnit::const_succ_iterator J = (*I)->Succs.begin(),
          JE = (*I)->Succs.end(); J != JE; ++J)
-      if (J->isCtrl())
+      if (J->isNormalMemoryOrBarrier())
         iterateChainSucc (AA, MFI, SU, J->getSUnit(),
                           ExitSU, &Depth, Visited);
   }