[llvm-branch-commits] [clang] [flang] [llvm] [openmp] [Clang][OpenMP] Add reverse and interchange directives (PR #92030)

[Alexey Bataev via llvm-branch-commits]

================
@@ -15745,6 +15760,388 @@ StmtResult SemaOpenMP::ActOnOpenMPUnrollDirective(ArrayRef<OMPClause *> Clauses,
                                     buildPreInits(Context, PreInits));
 }
 
+StmtResult
+SemaOpenMP::ActOnOpenMPReverseDirective(ArrayRef<OMPClause *> Clauses,
+                                        Stmt *AStmt, SourceLocation StartLoc,
+                                        SourceLocation EndLoc) {
+  ASTContext &Context = getASTContext();
+  Scope *CurScope = SemaRef.getCurScope();
+  assert(Clauses.empty() && "reverse directive does not accept any clauses; "
+                            "must have beed checked before");
+
+  // Empty statement should only be possible if there already was an error.
+  if (!AStmt)
+    return StmtError();
+
+  constexpr unsigned NumLoops = 1;
+  Stmt *Body = nullptr;
+  SmallVector<OMPLoopBasedDirective::HelperExprs, NumLoops> LoopHelpers(
+      NumLoops);
+  SmallVector<SmallVector<Stmt *, 0>, NumLoops + 1> OriginalInits;
+  if (!checkTransformableLoopNest(OMPD_reverse, AStmt, NumLoops, LoopHelpers,
+                                  Body, OriginalInits))
+    return StmtError();
+
+  // Delay applying the transformation to when template is completely
+  // instantiated.
+  if (SemaRef.CurContext->isDependentContext())
+    return OMPReverseDirective::Create(Context, StartLoc, EndLoc, Clauses,
+                                       AStmt, nullptr, nullptr);
+
+  assert(LoopHelpers.size() == NumLoops &&
+         "Expecting a single-dimensional loop iteration space");
+  assert(OriginalInits.size() == NumLoops &&
+         "Expecting a single-dimensional loop iteration space");
+  OMPLoopBasedDirective::HelperExprs &LoopHelper = LoopHelpers.front();
+
+  // Find the loop statement.
+  Stmt *LoopStmt = nullptr;
+  collectLoopStmts(AStmt, {LoopStmt});
+
+  // Determine the PreInit declarations.
+  SmallVector<Stmt *> PreInits;
+  addLoopPreInits(Context, LoopHelper, LoopStmt, OriginalInits[0], PreInits);
+
+  auto *IterationVarRef = cast<DeclRefExpr>(LoopHelper.IterationVarRef);
+  QualType IVTy = IterationVarRef->getType();
+  uint64_t IVWidth = Context.getTypeSize(IVTy);
+  auto *OrigVar = cast<DeclRefExpr>(LoopHelper.Counters.front());
+
+  // Iteration variable SourceLocations.
+  SourceLocation OrigVarLoc = OrigVar->getExprLoc();
+  SourceLocation OrigVarLocBegin = OrigVar->getBeginLoc();
+  SourceLocation OrigVarLocEnd = OrigVar->getEndLoc();
+
+  // Locations pointing to the transformation.
+  SourceLocation TransformLoc = StartLoc;
+  SourceLocation TransformLocBegin = StartLoc;
+  SourceLocation TransformLocEnd = EndLoc;
+
+  // Internal variable names.
+  std::string OrigVarName = OrigVar->getNameInfo().getAsString();
+  std::string TripCountName = (Twine(".tripcount.") + OrigVarName).str();
+  std::string ForwardIVName = (Twine(".forward.iv.") + OrigVarName).str();
+  std::string ReversedIVName = (Twine(".reversed.iv.") + OrigVarName).str();
+
+  // LoopHelper.Updates will read the logical iteration number from
+  // LoopHelper.IterationVarRef, compute the value of the user loop counter of
+  // that logical iteration from it, then assign it to the user loop counter
+  // variable. We cannot directly use LoopHelper.IterationVarRef as the
+  // induction variable of the generated loop because it may cause an underflow:
+  // \code
+  //   for (unsigned i = 0; i < n; ++i)
+  //     body(i);
+  // \endcode
+  //
+  // Naive reversal:
+  // \code
+  //   for (unsigned i = n-1; i >= 0; ++i)
----------------
alexey-bataev wrote:

```suggestion
  //   for (unsigned i = n-1; i >= 0; --i)
```


https://github.com/llvm/llvm-project/pull/92030