[flang][OpenMP] Overhaul implementation of ATOMIC construct (#137852)

The parser will accept a wide variety of illegal attempts at forming an
ATOMIC construct, leaving it to the semantic analysis to diagnose any
issues. This consolidates the analysis into one place and allows us to
produce more informative diagnostics.

The parser's outcome will be parser::OpenMPAtomicConstruct object
holding the directive, parser::Body, and an optional end-directive. The
prior variety of OmpAtomicXyz classes, as well as OmpAtomicClause have
been removed. READ, WRITE, etc. are now proper clauses.

The semantic analysis consistently operates on "evaluation"
representations, mainly evaluate::Expr (as SomeExpr) and
evaluate::Assignment. The results of the semantic analysis are stored in
a mutable member of the OpenMPAtomicConstruct node. This follows a
precedent of having `typedExpr` member in parser::Expr, for example.
This allows the lowering code to avoid duplicated handling of AST nodes.

Using a BLOCK construct containing multiple statements for an ATOMIC
construct that requires multiple statements is now allowed. In fact, any
nesting of such BLOCK constructs is allowed.

This implementation will parse, and perform semantic checks for both
conditional-update and conditional-update-capture, although no MLIR will
be generated for those. Instead, a TODO error will be issues prior to
lowering.

The allowed forms of the ATOMIC construct were based on the OpenMP 6.0
spec.

Author: kparzysz

flang/docs/OpenMPSupport.md

@@ -60,3 +60,16 @@ Note : No distinction is made between the support in Parser/Semantics, MLIR, Low
 | target teams distribute parallel loop construct            | P      | device, reduction and dist_schedule clauses are not supported |
 | teams distribute parallel loop simd construct              | P      | reduction, dist_schedule, and linear clauses are not supported |
 | target teams distribute parallel loop simd construct       | P      | device, reduction, dist_schedule and linear clauses are not supported |
+
+## Extensions
+### ATOMIC construct
+The implementation of the ATOMIC construct follows OpenMP 6.0 with the following extensions:
+- `x = x` is an allowed form of ATOMIC UPDATE.
+This is motivated by the fact that the equivalent forms `x = x+0` or `x = x*1` are allowed.
+- Explicit type conversions are allowed in ATOMIC READ, WRITE or UPDATE constructs, and in the capture statement in ATOMIC UPDATE CAPTURE.
+The OpenMP spec requires intrinsic- or pointer-assignments, which include (as per the Fortran standard) implicit type conversions.  Since such conversions need to be handled, allowing explicit conversions comes at no extra cost.
+- A literal `.true.` or `.false.` is an allowed condition in ATOMIC UPDATE COMPARE. [1]
+- A logical variable is an allowed form of the condition even if its value is not computed within the ATOMIC UPDATE COMPARE construct [1].
+- `expr equalop x` is an allowed condition in ATOMIC UPDATE COMPARE. [1]
+
+[1] Code generation for ATOMIC UPDATE COMPARE is not implemented yet.

flang/examples/FeatureList/FeatureList.cpp

@@ -445,13 +445,6 @@ struct NodeVisitor {
   READ_FEATURE(ObjectDecl)
   READ_FEATURE(OldParameterStmt)
   READ_FEATURE(OmpAlignedClause)
-  READ_FEATURE(OmpAtomic)
-  READ_FEATURE(OmpAtomicCapture)
-  READ_FEATURE(OmpAtomicCapture::Stmt1)
-  READ_FEATURE(OmpAtomicCapture::Stmt2)
-  READ_FEATURE(OmpAtomicRead)
-  READ_FEATURE(OmpAtomicUpdate)
-  READ_FEATURE(OmpAtomicWrite)
   READ_FEATURE(OmpBeginBlockDirective)
   READ_FEATURE(OmpBeginLoopDirective)
   READ_FEATURE(OmpBeginSectionsDirective)
@@ -480,7 +473,6 @@ struct NodeVisitor {
   READ_FEATURE(OmpIterationOffset)
   READ_FEATURE(OmpIterationVector)
   READ_FEATURE(OmpEndAllocators)
-  READ_FEATURE(OmpEndAtomic)
   READ_FEATURE(OmpEndBlockDirective)
   READ_FEATURE(OmpEndCriticalDirective)
   READ_FEATURE(OmpEndLoopDirective)
@@ -566,8 +558,6 @@ struct NodeVisitor {
   READ_FEATURE(OpenMPDeclareTargetConstruct)
   READ_FEATURE(OmpMemoryOrderType)
   READ_FEATURE(OmpMemoryOrderClause)
-  READ_FEATURE(OmpAtomicClause)
-  READ_FEATURE(OmpAtomicClauseList)
   READ_FEATURE(OmpAtomicDefaultMemOrderClause)
   READ_FEATURE(OpenMPFlushConstruct)
   READ_FEATURE(OpenMPLoopConstruct)

flang/examples/FlangOmpReport/FlangOmpReportVisitor.cpp

@@ -74,25 +74,19 @@ SourcePosition OpenMPCounterVisitor::getLocation(const OpenMPConstruct &c) {
           // the directive field.
           [&](const auto &c) -> SourcePosition {
             const CharBlock &source{std::get<0>(c.t).source};
-            return (parsing->allCooked().GetSourcePositionRange(source))->first;
+            return parsing->allCooked().GetSourcePositionRange(source)->first;
           },
           [&](const OpenMPAtomicConstruct &c) -> SourcePosition {
-            return std::visit(
-                [&](const auto &o) -> SourcePosition {
-                  const CharBlock &source{std::get<Verbatim>(o.t).source};
-                  return parsing->allCooked()
-                      .GetSourcePositionRange(source)
-                      ->first;
-                },
-                c.u);
+            const CharBlock &source{c.source};
+            return parsing->allCooked().GetSourcePositionRange(source)->first;
           },
           [&](const OpenMPSectionConstruct &c) -> SourcePosition {
             const CharBlock &source{c.source};
-            return (parsing->allCooked().GetSourcePositionRange(source))->first;
+            return parsing->allCooked().GetSourcePositionRange(source)->first;
           },
           [&](const OpenMPUtilityConstruct &c) -> SourcePosition {
             const CharBlock &source{c.source};
-            return (parsing->allCooked().GetSourcePositionRange(source))->first;
+            return parsing->allCooked().GetSourcePositionRange(source)->first;
           },
       },
       c.u);
@@ -157,14 +151,9 @@ std::string OpenMPCounterVisitor::getName(const OpenMPConstruct &c) {
             return normalize_construct_name(source.ToString());
           },
           [&](const OpenMPAtomicConstruct &c) -> std::string {
-            return std::visit(
-                [&](const auto &c) {
-                  // Get source from the verbatim fields
-                  const CharBlock &source{std::get<Verbatim>(c.t).source};
-                  return "atomic-" +
-                      normalize_construct_name(source.ToString());
-                },
-                c.u);
+            auto &dirSpec = std::get<OmpDirectiveSpecification>(c.t);
+            auto &dirName = std::get<OmpDirectiveName>(dirSpec.t);
+            return normalize_construct_name(dirName.source.ToString());
           },
           [&](const OpenMPUtilityConstruct &c) -> std::string {
             const CharBlock &source{c.source};

flang/include/flang/Parser/dump-parse-tree.h

@@ -532,15 +532,6 @@ class ParseTreeDumper {
   NODE(parser, OmpAtClause)
   NODE_ENUM(OmpAtClause, ActionTime)
   NODE_ENUM(OmpSeverityClause, Severity)
-  NODE(parser, OmpAtomic)
-  NODE(parser, OmpAtomicCapture)
-  NODE(OmpAtomicCapture, Stmt1)
-  NODE(OmpAtomicCapture, Stmt2)
-  NODE(parser, OmpAtomicCompare)
-  NODE(parser, OmpAtomicCompareIfStmt)
-  NODE(parser, OmpAtomicRead)
-  NODE(parser, OmpAtomicUpdate)
-  NODE(parser, OmpAtomicWrite)
   NODE(parser, OmpBeginBlockDirective)
   NODE(parser, OmpBeginLoopDirective)
   NODE(parser, OmpBeginSectionsDirective)
@@ -587,7 +578,6 @@ class ParseTreeDumper {
   NODE(parser, OmpDoacrossClause)
   NODE(parser, OmpDestroyClause)
   NODE(parser, OmpEndAllocators)
-  NODE(parser, OmpEndAtomic)
   NODE(parser, OmpEndBlockDirective)
   NODE(parser, OmpEndCriticalDirective)
   NODE(parser, OmpEndLoopDirective)
@@ -716,8 +706,6 @@ class ParseTreeDumper {
   NODE(parser, OpenMPDeclareMapperConstruct)
   NODE_ENUM(common, OmpMemoryOrderType)
   NODE(parser, OmpMemoryOrderClause)
-  NODE(parser, OmpAtomicClause)
-  NODE(parser, OmpAtomicClauseList)
   NODE(parser, OmpAtomicDefaultMemOrderClause)
   NODE(parser, OpenMPDepobjConstruct)
   NODE(parser, OpenMPUtilityConstruct)

flang/include/flang/Parser/parse-tree.h

@@ -4857,94 +4857,37 @@ struct OmpMemoryOrderClause {
   CharBlock source;
 };
 
-// 2.17.7 Atomic construct
-//        atomic-clause -> memory-order-clause | HINT(hint-expression) |
-//        FAIL(memory-order)
-struct OmpAtomicClause {
-  UNION_CLASS_BOILERPLATE(OmpAtomicClause);
-  CharBlock source;
-  std::variant<OmpMemoryOrderClause, OmpFailClause, OmpHintClause> u;
-};
-
-// atomic-clause-list -> [atomic-clause, [atomic-clause], ...]
-struct OmpAtomicClauseList {
-  WRAPPER_CLASS_BOILERPLATE(OmpAtomicClauseList, std::list<OmpAtomicClause>);
-  CharBlock source;
-};
-
-// END ATOMIC
-EMPTY_CLASS(OmpEndAtomic);
-
-// ATOMIC READ
-struct OmpAtomicRead {
-  TUPLE_CLASS_BOILERPLATE(OmpAtomicRead);
-  CharBlock source;
-  std::tuple<OmpAtomicClauseList, Verbatim, OmpAtomicClauseList,
-      Statement<AssignmentStmt>, std::optional<OmpEndAtomic>>
-      t;
-};
-
-// ATOMIC WRITE
-struct OmpAtomicWrite {
-  TUPLE_CLASS_BOILERPLATE(OmpAtomicWrite);
-  CharBlock source;
-  std::tuple<OmpAtomicClauseList, Verbatim, OmpAtomicClauseList,
-      Statement<AssignmentStmt>, std::optional<OmpEndAtomic>>
-      t;
-};
-
-// ATOMIC UPDATE
-struct OmpAtomicUpdate {
-  TUPLE_CLASS_BOILERPLATE(OmpAtomicUpdate);
-  CharBlock source;
-  std::tuple<OmpAtomicClauseList, Verbatim, OmpAtomicClauseList,
-      Statement<AssignmentStmt>, std::optional<OmpEndAtomic>>
-      t;
-};
-
-// ATOMIC CAPTURE
-struct OmpAtomicCapture {
-  TUPLE_CLASS_BOILERPLATE(OmpAtomicCapture);
-  CharBlock source;
-  WRAPPER_CLASS(Stmt1, Statement<AssignmentStmt>);
-  WRAPPER_CLASS(Stmt2, Statement<AssignmentStmt>);
-  std::tuple<OmpAtomicClauseList, Verbatim, OmpAtomicClauseList, Stmt1, Stmt2,
-      OmpEndAtomic>
-      t;
-};
-
-struct OmpAtomicCompareIfStmt {
-  UNION_CLASS_BOILERPLATE(OmpAtomicCompareIfStmt);
-  std::variant<common::Indirection<IfStmt>, common::Indirection<IfConstruct>> u;
-};
-
-// ATOMIC COMPARE (OpenMP 5.1, OPenMP 5.2 spec: 15.8.4)
-struct OmpAtomicCompare {
-  TUPLE_CLASS_BOILERPLATE(OmpAtomicCompare);
+struct OpenMPAtomicConstruct {
+  llvm::omp::Clause GetKind() const;
+  bool IsCapture() const;
+  bool IsCompare() const;
+  TUPLE_CLASS_BOILERPLATE(OpenMPAtomicConstruct);
   CharBlock source;
-  std::tuple<OmpAtomicClauseList, Verbatim, OmpAtomicClauseList,
-      OmpAtomicCompareIfStmt, std::optional<OmpEndAtomic>>
+  std::tuple<OmpDirectiveSpecification, Block,
+      std::optional<OmpDirectiveSpecification>>
       t;
-};
 
-// ATOMIC
-struct OmpAtomic {
-  TUPLE_CLASS_BOILERPLATE(OmpAtomic);
-  CharBlock source;
-  std::tuple<Verbatim, OmpAtomicClauseList, Statement<AssignmentStmt>,
-      std::optional<OmpEndAtomic>>
-      t;
-};
+  // Information filled out during semantic checks to avoid duplication
+  // of analyses.
+  struct Analysis {
+    static constexpr int None = 0;
+    static constexpr int Read = 1;
+    static constexpr int Write = 2;
+    static constexpr int Update = Read | Write;
+    static constexpr int Action = 3; // Bitmask for None, Read, Write, Update
+    static constexpr int IfTrue = 4;
+    static constexpr int IfFalse = 8;
+    static constexpr int Condition = 12; // Bitmask for IfTrue, IfFalse
+
+    struct Op {
+      int what;
+      AssignmentStmt::TypedAssignment assign;
+    };
+    TypedExpr atom, cond;
+    Op op0, op1;
+  };
 
-// 2.17.7 atomic ->
-//        ATOMIC [atomic-clause-list] atomic-construct [atomic-clause-list] |
-//        ATOMIC [atomic-clause-list]
-//        atomic-construct -> READ | WRITE | UPDATE | CAPTURE | COMPARE
-struct OpenMPAtomicConstruct {
-  UNION_CLASS_BOILERPLATE(OpenMPAtomicConstruct);
-  std::variant<OmpAtomicRead, OmpAtomicWrite, OmpAtomicCapture, OmpAtomicUpdate,
-      OmpAtomicCompare, OmpAtomic>
-      u;
+  mutable Analysis analysis;
 };
 
 // OpenMP directives that associate with loop(s)