[Attributor] Add an option to increase the max number of iterations

Right now the Attributor defaults to 32 fixed point iterations unless it is set
explicitly by a command line flag. This patch allows this to be configured when
the attributor instance is created. The maximum is then increased in OpenMPOpt
if the target is a kernel. This is because the globalization analysis can result
in larger iteration counts due to many dependent instances running at once.

Depends on D102444

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D104416

include/llvm/Transforms/IPO/Attributor.h

@@ -1090,6 +1090,8 @@ struct Attributor {
   /// \param Allowed If not null, a set limiting the attribute opportunities.
   /// \param DeleteFns Whether to delete functions.
   /// \param RewriteSignatures Whether to rewrite function signatures.
+  /// \param MaxFixedPointIterations Maximum number of iterations to run until
+  ///                                fixpoint.
   Attributor(SetVector<Function *> &Functions, InformationCache &InfoCache,
              CallGraphUpdater &CGUpdater,
              DenseSet<const char *> *Allowed = nullptr, bool DeleteFns = true,
@@ -1097,7 +1099,7 @@ struct Attributor {
       : Allocator(InfoCache.Allocator), Functions(Functions),
         InfoCache(InfoCache), CGUpdater(CGUpdater), Allowed(Allowed),
         DeleteFns(DeleteFns), RewriteSignatures(RewriteSignatures),
-        OREGetter(None), PassName("") {}
+        MaxFixpointIterations(None), OREGetter(None), PassName("")  {}
 
   /// Constructor
   ///
@@ -1107,16 +1109,20 @@ struct Attributor {
   /// \param CGUpdater Helper to update an underlying call graph.
   /// \param Allowed If not null, a set limiting the attribute opportunities.
   /// \param DeleteFns Whether to delete functions
+  /// \param MaxFixedPointIterations Maximum number of iterations to run until
+  ///                                fixpoint.
   /// \param OREGetter A callback function that returns an ORE object from a
   ///                  Function pointer.
   /// \param PassName  The name of the pass emitting remarks.
   Attributor(SetVector<Function *> &Functions, InformationCache &InfoCache,
              CallGraphUpdater &CGUpdater, DenseSet<const char *> *Allowed,
              bool DeleteFns, bool RewriteSignatures,
+             Optional<unsigned> MaxFixpointIterations,
              OptimizationRemarkGetter OREGetter, const char *PassName)
       : Allocator(InfoCache.Allocator), Functions(Functions),
         InfoCache(InfoCache), CGUpdater(CGUpdater), Allowed(Allowed),
         DeleteFns(DeleteFns), RewriteSignatures(RewriteSignatures),
+        MaxFixpointIterations(MaxFixpointIterations),
         OREGetter(Optional<OptimizationRemarkGetter>(OREGetter)),
         PassName(PassName) {}
 
@@ -1859,6 +1865,9 @@ private:
   /// Whether to rewrite signatures.
   const bool RewriteSignatures;
 
+  /// Maximum number of fixedpoint iterations.
+  Optional<unsigned> MaxFixpointIterations;
+
   /// A set to remember the functions we already assume to be live and visited.
   DenseSet<const Function *> VisitedFunctions;
 

lib/Transforms/IPO/Attributor.cpp

@@ -77,7 +77,7 @@ STATISTIC(NumAttributesManifested,
 // This will become more evolved once we perform two interleaved fixpoint
 // iterations: bottom-up and top-down.
 static cl::opt<unsigned>
-    MaxFixpointIterations("attributor-max-iterations", cl::Hidden,
+    SetFixpointIterations("attributor-max-iterations", cl::Hidden,
                           cl::desc("Maximal number of fixpoint iterations."),
                           cl::init(32));
 
@@ -1069,6 +1069,12 @@ void Attributor::runTillFixpoint() {
   // the abstract analysis.
 
   unsigned IterationCounter = 1;
+  unsigned MaxFixedPointIterations;
+  if (MaxFixpointIterations)
+    MaxFixedPointIterations = MaxFixpointIterations.getValue();
+  else
+    MaxFixedPointIterations = SetFixpointIterations;
+
 
   SmallVector<AbstractAttribute *, 32> ChangedAAs;
   SetVector<AbstractAttribute *> Worklist, InvalidAAs;
@@ -1148,7 +1154,7 @@ void Attributor::runTillFixpoint() {
     Worklist.clear();
     Worklist.insert(ChangedAAs.begin(), ChangedAAs.end());
 
-  } while (!Worklist.empty() && (IterationCounter++ < MaxFixpointIterations ||
+  } while (!Worklist.empty() && (IterationCounter++ < MaxFixedPointIterations ||
                                  VerifyMaxFixpointIterations));
 
   LLVM_DEBUG(dbgs() << "\n[Attributor] Fixpoint iteration done after: "
@@ -1187,9 +1193,9 @@ void Attributor::runTillFixpoint() {
   });
 
   if (VerifyMaxFixpointIterations &&
-      IterationCounter != MaxFixpointIterations) {
+      IterationCounter != MaxFixedPointIterations) {
     errs() << "\n[Attributor] Fixpoint iteration done after: "
-           << IterationCounter << "/" << MaxFixpointIterations
+           << IterationCounter << "/" << MaxFixedPointIterations
            << " iterations\n";
     llvm_unreachable("The fixpoint was not reached with exactly the number of "
                      "specified iterations!");

lib/Transforms/IPO/OpenMPOpt.cpp

@@ -2666,7 +2666,8 @@ PreservedAnalyses OpenMPOptPass::run(Module &M, ModuleAnalysisManager &AM) {
   OMPInformationCache InfoCache(M, AG, Allocator, /*CGSCC*/ Functions,
                                 OMPInModule.getKernels());
 
-  Attributor A(Functions, InfoCache, CGUpdater, nullptr, true, false, OREGetter,
+  unsigned MaxFixponitIterations = (!OMPInModule.getKernels().empty()) ? 64 : 32;
+  Attributor A(Functions, InfoCache, CGUpdater, nullptr, true, false, MaxFixponitIterations, OREGetter,
                DEBUG_TYPE);
 
   OpenMPOpt OMPOpt(SCC, CGUpdater, OREGetter, InfoCache, A);
@@ -2722,7 +2723,8 @@ PreservedAnalyses OpenMPOptCGSCCPass::run(LazyCallGraph::SCC &C,
   OMPInformationCache InfoCache(*(Functions.back()->getParent()), AG, Allocator,
                                 /*CGSCC*/ Functions, OMPInModule.getKernels());
 
-  Attributor A(Functions, InfoCache, CGUpdater, nullptr, false, true, OREGetter,
+  unsigned MaxFixponitIterations = (!OMPInModule.getKernels().empty()) ? 64 : 32;
+  Attributor A(Functions, InfoCache, CGUpdater, nullptr, false, true, MaxFixponitIterations, OREGetter,
                DEBUG_TYPE);
 
   OpenMPOpt OMPOpt(SCC, CGUpdater, OREGetter, InfoCache, A);
@@ -2799,8 +2801,9 @@ struct OpenMPOptCGSCCLegacyPass : public CallGraphSCCPass {
         *(Functions.back()->getParent()), AG, Allocator,
         /*CGSCC*/ Functions, OMPInModule.getKernels());
 
+    unsigned MaxFixponitIterations = (!OMPInModule.getKernels().empty()) ? 64 : 32;
     Attributor A(Functions, InfoCache, CGUpdater, nullptr, false, true,
-                 OREGetter, DEBUG_TYPE);
+                 MaxFixponitIterations, OREGetter, DEBUG_TYPE);
 
     OpenMPOpt OMPOpt(SCC, CGUpdater, OREGetter, InfoCache, A);
     return OMPOpt.run(false);