Run VerifyDAGDiverence in debug only

[mikael]

Summary

VerifyDAGDiverence cost compilation time, avoid running it in non-debug
builds.

[alex-t]

TargetTransformInfo::hasBranchDivergence() only returns true only if the divergence makes sense for the given target.
So, the compile time should be only affected for such targets: AMDGPU, NVPTX etc.

On which target have you observed compile time increase? How much (% of the whole selection pass) was it affected?

I also initially planned to put the DAG verification under #ifdef NDEBUG.
My change was reviewed by Eli Friedman and he insisted on DAG verification for non-debug builds.
Maybe we should make him know that we changed this?

[mikael]

The compile time increase showed up in our internal GPU target.

[efriedma]

It's okay not to run the verifier in Release mode if it's hurting performance. I'm a bit surprised it's actually measurable, but I guess adding a bunch of extra walks over the DAG could add up to a few percent.

LGTM

include/llvm/CodeGen/SelectionDAG.h

const SDValue &setRoot(SDValue N) {
     if (N.getNode())
       checkForCycles(N.getNode(), this);
     Root = N;
     if (N.getNode())
       checkForCycles(this);
     return Root;
   }
 
+#ifndef NDEBUG
   void VerifyDAGDiverence();
+#endif
 
   /// This iterates over the nodes in the SelectionDAG, folding
   /// certain types of nodes together, or eliminating superfluous nodes.  The
   /// Level argument controls whether Combine is allowed to produce nodes and
   /// types that are illegal on the target.
   void Combine(CombineLevel Level, AliasAnalysis *AA,
                CodeGenOpt::Level OptLevel);
 

lib/CodeGen/SelectionDAG/SelectionDAG.cpp

I!=Order.end();++I) {
     for (auto U : N->uses()) {
       unsigned &UnsortedOps = Degree[U];
       if (0 == --UnsortedOps)
         Order.push_back(U);
     }
   }
 }
 
+#ifndef NDEBUG
 void SelectionDAG::VerifyDAGDiverence()
 {
   std::vector<SDNode*> TopoOrder;
   CreateTopologicalOrder(TopoOrder);
   const TargetLowering &TLI = getTargetLoweringInfo();
   DenseMap<const SDNode *, bool> DivergenceMap;
   for (auto &N : allnodes()) {
     DivergenceMap[&N] = false;
for (auto N : TopoOrder) {
     }
   }
   for (auto &N : allnodes()) {
     (void)N;
     assert(DivergenceMap[&N] == N.isDivergent() &&
            "Divergence bit inconsistency detected\n");
   }
 }
+#endif
 
 
 /// ReplaceAllUsesOfValuesWith - Replace any uses of From with To, leaving
 /// uses of other values produced by From.getNode() alone.  The same value
 /// may appear in both the From and To list.  The Deleted vector is
 /// handled the same way as for ReplaceAllUsesWith.
 void SelectionDAG::ReplaceAllUsesOfValuesWith(const SDValue *From,
                                               const SDValue *To,

lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp

 
 void SelectionDAGISel::CodeGenAndEmitDAG() {
   StringRef GroupName = "sdag";
   StringRef GroupDescription = "Instruction Selection and Scheduling";
   std::string BlockName;
   int BlockNumber = -1;
   (void)BlockNumber;
   bool MatchFilterBB = false; (void)MatchFilterBB;
+#ifndef NDEBUG
   TargetTransformInfo &TTI =
       getAnalysis<TargetTransformInfoWrapperPass>().getTTI(*FuncInfo->Fn);
+#endif
 
   // Pre-type legalization allow creation of any node types.
   CurDAG->NewNodesMustHaveLegalTypes = false;
 
 #ifndef NDEBUG
   MatchFilterBB = (FilterDAGBasicBlockName.empty() ||
                    FilterDAGBasicBlockName ==
                        FuncInfo->MBB->getBasicBlock()->getName());
#endif
 
   // Run the DAG combiner in pre-legalize mode.
   {
     NamedRegionTimer T("combine1", "DAG Combining 1", GroupName,
                        GroupDescription, TimePassesIsEnabled);
     CurDAG->Combine(BeforeLegalizeTypes, AA, OptLevel);
   }
 
+#ifndef NDEBUG
   if (TTI.hasBranchDivergence())
     CurDAG->VerifyDAGDiverence();
+#endif
 
   LLVM_DEBUG(dbgs() << "Optimized lowered selection DAG: "
                     << printMBBReference(*FuncInfo->MBB) << " '" << BlockName
                     << "'\n";
              CurDAG->dump());
 
   // Second step, hack on the DAG until it only uses operations and types that
   // the target supports.
   if (ViewLegalizeTypesDAGs && MatchFilterBB)
     CurDAG->viewGraph("legalize-types input for " + BlockName);
 
   bool Changed;
   {
     NamedRegionTimer T("legalize_types", "Type Legalization", GroupName,
                        GroupDescription, TimePassesIsEnabled);
     Changed = CurDAG->LegalizeTypes();
   }
 
+#ifndef NDEBUG
   if (TTI.hasBranchDivergence())
     CurDAG->VerifyDAGDiverence();
+#endif
 
   LLVM_DEBUG(dbgs() << "Type-legalized selection DAG: "
                     << printMBBReference(*FuncInfo->MBB) << " '" << BlockName
                     << "'\n";
              CurDAG->dump());
 
   // Only allow creation of legal node types.
   CurDAG->NewNodesMustHaveLegalTypes = true;
 
   if (Changed) {
     if (ViewDAGCombineLT && MatchFilterBB)
       CurDAG->viewGraph("dag-combine-lt input for " + BlockName);
 
     // Run the DAG combiner in post-type-legalize mode.
     {
       NamedRegionTimer T("combine_lt", "DAG Combining after legalize types",
                          GroupName, GroupDescription, TimePassesIsEnabled);
       CurDAG->Combine(AfterLegalizeTypes, AA, OptLevel);
     }
 
+#ifndef NDEBUG
     if (TTI.hasBranchDivergence())
       CurDAG->VerifyDAGDiverence();
+#endif
 
     LLVM_DEBUG(dbgs() << "Optimized type-legalized selection DAG: "
                       << printMBBReference(*FuncInfo->MBB) << " '" << BlockName
                       << "'\n";
                CurDAG->dump());
   }
 
   {
// Run the DAG combiner in post-type-legalize mode.
       CurDAG->Combine(AfterLegalizeVectorOps, AA, OptLevel);
     }
 
     LLVM_DEBUG(dbgs() << "Optimized vector-legalized selection DAG: "
                       << printMBBReference(*FuncInfo->MBB) << " '" << BlockName
                       << "'\n";
                CurDAG->dump());
 
+#ifndef NDEBUG
     if (TTI.hasBranchDivergence())
       CurDAG->VerifyDAGDiverence();
+#endif
   }
 
   if (ViewLegalizeDAGs && MatchFilterBB)
     CurDAG->viewGraph("legalize input for " + BlockName);
 
   {
     NamedRegionTimer T("legalize", "DAG Legalization", GroupName,
                        GroupDescription, TimePassesIsEnabled);
     CurDAG->Legalize();
   }
 
+#ifndef NDEBUG
   if (TTI.hasBranchDivergence())
     CurDAG->VerifyDAGDiverence();
+#endif
 
   LLVM_DEBUG(dbgs() << "Legalized selection DAG: "
                     << printMBBReference(*FuncInfo->MBB) << " '" << BlockName
                     << "'\n";
              CurDAG->dump());
 
   if (ViewDAGCombine2 && MatchFilterBB)
     CurDAG->viewGraph("dag-combine2 input for " + BlockName);
 
   // Run the DAG combiner in post-legalize mode.
   {
     NamedRegionTimer T("combine2", "DAG Combining 2", GroupName,
                        GroupDescription, TimePassesIsEnabled);
     CurDAG->Combine(AfterLegalizeDAG, AA, OptLevel);
   }
 
+#ifndef NDEBUG
   if (TTI.hasBranchDivergence())
     CurDAG->VerifyDAGDiverence();
+#endif
 
   LLVM_DEBUG(dbgs() << "Optimized legalized selection DAG: "
                     << printMBBReference(*FuncInfo->MBB) << " '" << BlockName
                     << "'\n";
              CurDAG->dump());
 
   if (OptLevel != CodeGenOpt::None)
     ComputeLiveOutVRegInfo();