[flang][OpenMP][NFC] remove globals with mlir::StateStack (#144898)

Idea suggested by @skatrak

flang/include/flang/Lower/AbstractConverter.h

@@ -26,6 +26,7 @@
 
 namespace mlir {
 class SymbolTable;
+class StateStack;
 }
 
 namespace fir {
@@ -361,6 +362,8 @@ public:
   /// functions in order to be in sync).
   virtual mlir::SymbolTable *getMLIRSymbolTable() = 0;
 
+  virtual mlir::StateStack &getStateStack() = 0;
+
 private:
   /// Options controlling lowering behavior.
   const Fortran::lower::LoweringOptions &loweringOptions;

flang/lib/Lower/Bridge.cpp

@@ -69,6 +69,7 @@
 #include "mlir/IR/Matchers.h"
 #include "mlir/IR/PatternMatch.h"
 #include "mlir/Parser/Parser.h"
+#include "mlir/Support/StateStack.h"
 #include "mlir/Transforms/RegionUtils.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringSet.h"
@@ -1237,6 +1238,8 @@ private:
 
   mlir::SymbolTable *getMLIRSymbolTable() override { return &mlirSymbolTable; }
 
+  mlir::StateStack &getStateStack() override { return stateStack; }
+
   /// Add the symbol to the local map and return `true`. If the symbol is
   /// already in the map and \p forced is `false`, the map is not updated.
   /// Instead the value `false` is returned.
@@ -6552,6 +6555,9 @@ private:
   /// attribute since mlirSymbolTable must pro-actively be maintained when
   /// new Symbol operations are created.
   mlir::SymbolTable mlirSymbolTable;
+
+  /// Used to store context while recursing into regions during lowering.
+  mlir::StateStack stateStack;
 };
 
 } // namespace

flang/lib/Lower/OpenMP/OpenMP.cpp

@@ -39,6 +39,7 @@
 #include "flang/Support/OpenMP-utils.h"
 #include "mlir/Dialect/ControlFlow/IR/ControlFlowOps.h"
 #include "mlir/Dialect/OpenMP/OpenMPDialect.h"
+#include "mlir/Support/StateStack.h"
 #include "mlir/Transforms/RegionUtils.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/Frontend/OpenMP/OMPConstants.h"
@@ -198,9 +199,41 @@ private:
 /// the handling of the outer region by keeping a stack of information
 /// structures, but it will probably still require some further work to support
 /// reverse offloading.
-static llvm::SmallVector<HostEvalInfo, 0> hostEvalInfo;
-static llvm::SmallVector<const parser::OpenMPSectionsConstruct *, 0>
-    sectionsStack;
+class HostEvalInfoStackFrame
+    : public mlir::StateStackFrameBase<HostEvalInfoStackFrame> {
+public:
+  MLIR_DEFINE_EXPLICIT_INTERNAL_INLINE_TYPE_ID(HostEvalInfoStackFrame)
+
+  HostEvalInfo info;
+};
+
+static HostEvalInfo *
+getHostEvalInfoStackTop(lower::AbstractConverter &converter) {
+  HostEvalInfoStackFrame *frame =
+      converter.getStateStack().getStackTop<HostEvalInfoStackFrame>();
+  return frame ? &frame->info : nullptr;
+}
+
+/// Stack frame for storing the OpenMPSectionsConstruct currently being
+/// processed so that it can be referred to when lowering the construct.
+class SectionsConstructStackFrame
+    : public mlir::StateStackFrameBase<SectionsConstructStackFrame> {
+public:
+  MLIR_DEFINE_EXPLICIT_INTERNAL_INLINE_TYPE_ID(SectionsConstructStackFrame)
+
+  explicit SectionsConstructStackFrame(
+      const parser::OpenMPSectionsConstruct &sectionsConstruct)
+      : sectionsConstruct{sectionsConstruct} {}
+
+  const parser::OpenMPSectionsConstruct &sectionsConstruct;
+};
+
+static const parser::OpenMPSectionsConstruct *
+getSectionsConstructStackTop(lower::AbstractConverter &converter) {
+  SectionsConstructStackFrame *frame =
+      converter.getStateStack().getStackTop<SectionsConstructStackFrame>();
+  return frame ? &frame->sectionsConstruct : nullptr;
+}
 
 /// Bind symbols to their corresponding entry block arguments.
 ///
@@ -535,31 +568,32 @@ static void processHostEvalClauses(lower::AbstractConverter &converter,
     if (!ompEval)
       return;
 
-    HostEvalInfo &hostInfo = hostEvalInfo.back();
+    HostEvalInfo *hostInfo = getHostEvalInfoStackTop(converter);
+    assert(hostInfo && "expected HOST_EVAL info structure");
 
     switch (extractOmpDirective(*ompEval)) {
     case OMPD_teams_distribute_parallel_do:
     case OMPD_teams_distribute_parallel_do_simd:
-      cp.processThreadLimit(stmtCtx, hostInfo.ops);
+      cp.processThreadLimit(stmtCtx, hostInfo->ops);
       [[fallthrough]];
     case OMPD_target_teams_distribute_parallel_do:
     case OMPD_target_teams_distribute_parallel_do_simd:
-      cp.processNumTeams(stmtCtx, hostInfo.ops);
+      cp.processNumTeams(stmtCtx, hostInfo->ops);
       [[fallthrough]];
     case OMPD_distribute_parallel_do:
     case OMPD_distribute_parallel_do_simd:
-      cp.processNumThreads(stmtCtx, hostInfo.ops);
+      cp.processNumThreads(stmtCtx, hostInfo->ops);
       [[fallthrough]];
     case OMPD_distribute:
     case OMPD_distribute_simd:
-      cp.processCollapse(loc, eval, hostInfo.ops, hostInfo.iv);
+      cp.processCollapse(loc, eval, hostInfo->ops, hostInfo->iv);
       break;
 
     case OMPD_teams:
-      cp.processThreadLimit(stmtCtx, hostInfo.ops);
+      cp.processThreadLimit(stmtCtx, hostInfo->ops);
       [[fallthrough]];
     case OMPD_target_teams:
-      cp.processNumTeams(stmtCtx, hostInfo.ops);
+      cp.processNumTeams(stmtCtx, hostInfo->ops);
       processSingleNestedIf([](Directive nestedDir) {
         return topDistributeSet.test(nestedDir) || topLoopSet.test(nestedDir);
       });
@@ -567,22 +601,22 @@ static void processHostEvalClauses(lower::AbstractConverter &converter,
 
     case OMPD_teams_distribute:
     case OMPD_teams_distribute_simd:
-      cp.processThreadLimit(stmtCtx, hostInfo.ops);
+      cp.processThreadLimit(stmtCtx, hostInfo->ops);
       [[fallthrough]];
     case OMPD_target_teams_distribute:
     case OMPD_target_teams_distribute_simd:
-      cp.processCollapse(loc, eval, hostInfo.ops, hostInfo.iv);
-      cp.processNumTeams(stmtCtx, hostInfo.ops);
+      cp.processCollapse(loc, eval, hostInfo->ops, hostInfo->iv);
+      cp.processNumTeams(stmtCtx, hostInfo->ops);
       break;
 
     case OMPD_teams_loop:
-      cp.processThreadLimit(stmtCtx, hostInfo.ops);
+      cp.processThreadLimit(stmtCtx, hostInfo->ops);
       [[fallthrough]];
     case OMPD_target_teams_loop:
-      cp.processNumTeams(stmtCtx, hostInfo.ops);
+      cp.processNumTeams(stmtCtx, hostInfo->ops);
       [[fallthrough]];
     case OMPD_loop:
-      cp.processCollapse(loc, eval, hostInfo.ops, hostInfo.iv);
+      cp.processCollapse(loc, eval, hostInfo->ops, hostInfo->iv);
       break;
 
     // Standalone 'target' case.
@@ -596,8 +630,6 @@ static void processHostEvalClauses(lower::AbstractConverter &converter,
     }
   };
 
-  assert(!hostEvalInfo.empty() && "expected HOST_EVAL info structure");
-
   const auto *ompEval = eval.getIf<parser::OpenMPConstruct>();
   assert(ompEval &&
          llvm::omp::allTargetSet.test(extractOmpDirective(*ompEval)) &&
@@ -1456,8 +1488,8 @@ static void genBodyOfTargetOp(
   mlir::Region &region = targetOp.getRegion();
   mlir::Block *entryBlock = genEntryBlock(firOpBuilder, args, region);
   bindEntryBlockArgs(converter, targetOp, args);
-  if (!hostEvalInfo.empty())
-    hostEvalInfo.back().bindOperands(argIface.getHostEvalBlockArgs());
+  if (HostEvalInfo *hostEvalInfo = getHostEvalInfoStackTop(converter))
+    hostEvalInfo->bindOperands(argIface.getHostEvalBlockArgs());
 
   // Check if cloning the bounds introduced any dependency on the outer region.
   // If so, then either clone them as well if they are MemoryEffectFree, or else
@@ -1696,7 +1728,8 @@ genLoopNestClauses(lower::AbstractConverter &converter,
                    llvm::SmallVectorImpl<const semantics::Symbol *> &iv) {
   ClauseProcessor cp(converter, semaCtx, clauses);
 
-  if (hostEvalInfo.empty() || !hostEvalInfo.back().apply(clauseOps, iv))
+  HostEvalInfo *hostEvalInfo = getHostEvalInfoStackTop(converter);
+  if (!hostEvalInfo || !hostEvalInfo->apply(clauseOps, iv))
     cp.processCollapse(loc, eval, clauseOps, iv);
 
   clauseOps.loopInclusive = converter.getFirOpBuilder().getUnitAttr();
@@ -1741,7 +1774,8 @@ static void genParallelClauses(
   cp.processAllocate(clauseOps);
   cp.processIf(llvm::omp::Directive::OMPD_parallel, clauseOps);
 
-  if (hostEvalInfo.empty() || !hostEvalInfo.back().apply(clauseOps))
+  HostEvalInfo *hostEvalInfo = getHostEvalInfoStackTop(converter);
+  if (!hostEvalInfo || !hostEvalInfo->apply(clauseOps))
     cp.processNumThreads(stmtCtx, clauseOps);
 
   cp.processProcBind(clauseOps);
@@ -1812,10 +1846,10 @@ static void genTargetClauses(
   cp.processDepend(symTable, stmtCtx, clauseOps);
   cp.processDevice(stmtCtx, clauseOps);
   cp.processHasDeviceAddr(stmtCtx, clauseOps, hasDeviceAddrSyms);
-  if (!hostEvalInfo.empty()) {
+  if (HostEvalInfo *hostEvalInfo = getHostEvalInfoStackTop(converter)) {
     // Only process host_eval if compiling for the host device.
     processHostEvalClauses(converter, semaCtx, stmtCtx, eval, loc);
-    hostEvalInfo.back().collectValues(clauseOps.hostEvalVars);
+    hostEvalInfo->collectValues(clauseOps.hostEvalVars);
   }
   cp.processIf(llvm::omp::Directive::OMPD_target, clauseOps);
   cp.processIsDevicePtr(clauseOps, isDevicePtrSyms);
@@ -1952,7 +1986,8 @@ static void genTeamsClauses(
   cp.processAllocate(clauseOps);
   cp.processIf(llvm::omp::Directive::OMPD_teams, clauseOps);
 
-  if (hostEvalInfo.empty() || !hostEvalInfo.back().apply(clauseOps)) {
+  HostEvalInfo *hostEvalInfo = getHostEvalInfoStackTop(converter);
+  if (!hostEvalInfo || !hostEvalInfo->apply(clauseOps)) {
     cp.processNumTeams(stmtCtx, clauseOps);
     cp.processThreadLimit(stmtCtx, clauseOps);
   }
@@ -2204,19 +2239,18 @@ genScanOp(lower::AbstractConverter &converter, lower::SymMap &symTable,
       converter.getCurrentLocation(), clauseOps);
 }
 
-/// This breaks the normal prototype of the gen*Op functions: adding the
-/// sectionBlocks argument so that the enclosed section constructs can be
-/// lowered here with correct reduction symbol remapping.
 static mlir::omp::SectionsOp
 genSectionsOp(lower::AbstractConverter &converter, lower::SymMap &symTable,
               semantics::SemanticsContext &semaCtx,
               lower::pft::Evaluation &eval, mlir::Location loc,
               const ConstructQueue &queue,
               ConstructQueue::const_iterator item) {
-  assert(!sectionsStack.empty());
+  const parser::OpenMPSectionsConstruct *sectionsConstruct =
+      getSectionsConstructStackTop(converter);
+  assert(sectionsConstruct && "Missing additional parsing information");
+
   const auto &sectionBlocks =
-      std::get<parser::OmpSectionBlocks>(sectionsStack.back()->t);
-  sectionsStack.pop_back();
+      std::get<parser::OmpSectionBlocks>(sectionsConstruct->t);
   mlir::omp::SectionsOperands clauseOps;
   llvm::SmallVector<const semantics::Symbol *> reductionSyms;
   genSectionsClauses(converter, semaCtx, item->clauses, loc, clauseOps,
@@ -2370,7 +2404,7 @@ genTargetOp(lower::AbstractConverter &converter, lower::SymMap &symTable,
 
   // Introduce a new host_eval information structure for this target region.
   if (!isTargetDevice)
-    hostEvalInfo.emplace_back();
+    converter.getStateStack().stackPush<HostEvalInfoStackFrame>();
 
   mlir::omp::TargetOperands clauseOps;
   DefaultMapsTy defaultMaps;
@@ -2497,7 +2531,7 @@ genTargetOp(lower::AbstractConverter &converter, lower::SymMap &symTable,
 
   // Remove the host_eval information structure created for this target region.
   if (!isTargetDevice)
-    hostEvalInfo.pop_back();
+    converter.getStateStack().stackPop();
   return targetOp;
 }
 
@@ -3771,7 +3805,8 @@ static void genOMP(lower::AbstractConverter &converter, lower::SymMap &symTable,
       buildConstructQueue(converter.getFirOpBuilder().getModule(), semaCtx,
                           eval, source, directive, clauses)};
 
-  sectionsStack.push_back(&sectionsConstruct);
+  mlir::SaveStateStack<SectionsConstructStackFrame> saveStateStack{
+      converter.getStateStack(), sectionsConstruct};
   genOMPDispatch(converter, symTable, semaCtx, eval, currentLocation, queue,
                  queue.begin());
 }

mlir/include/mlir/Support/StateStack.h

@@ -84,6 +84,17 @@ public:
     return WalkResult::advance();
   }
 
+  /// Get the top instance of frame type `T` or nullptr if none are found
+  template <typename T>
+  T *getStackTop() {
+    T *top = nullptr;
+    stackWalk<T>([&](T &frame) -> mlir::WalkResult {
+      top = &frame;
+      return mlir::WalkResult::interrupt();
+    });
+    return top;
+  }
+
 private:
   SmallVector<std::unique_ptr<StateStackFrame>> stack;
 };