[clang] [flang] [llvm] [openmp] [Clang][OpenMP][LoopTransformations] Add support for "#pragma omp fuse" loop transformation directive and "looprange" clause (PR #139293)

[Alexey Bataev via llvm-commits]

================
@@ -15716,6 +15987,489 @@ StmtResult SemaOpenMP::ActOnOpenMPInterchangeDirective(
                                          buildPreInits(Context, PreInits));
 }
 
+StmtResult SemaOpenMP::ActOnOpenMPFuseDirective(ArrayRef<OMPClause *> Clauses,
+                                                Stmt *AStmt,
+                                                SourceLocation StartLoc,
+                                                SourceLocation EndLoc) {
+
+  ASTContext &Context = getASTContext();
+  DeclContext *CurrContext = SemaRef.CurContext;
+  Scope *CurScope = SemaRef.getCurScope();
+  CaptureVars CopyTransformer(SemaRef);
+
+  // Ensure the structured block is not empty
+  if (!AStmt)
+    return StmtError();
+
+  // Defer transformation in dependent contexts
+  // The NumLoopNests argument is set to a placeholder 1 (even though
+  // using looprange fuse could yield up to 3 top level loop nests)
+  // because a dependent context could prevent determining its true value
+  if (CurrContext->isDependentContext()) {
+    return OMPFuseDirective::Create(Context, StartLoc, EndLoc, Clauses,
+                                    /* NumLoops */ 1, /* LoopSeqSize */ 1,
+                                    AStmt, nullptr, nullptr);
+  }
+
+  // Validate that the potential loop sequence is transformable for fusion
+  // Also collect the HelperExprs, Loop Stmts, Inits, and Number of loops
+  LoopSequenceAnalysis SeqAnalysis;
+  if (!checkTransformableLoopSequence(OMPD_fuse, AStmt, SeqAnalysis, Context))
+    return StmtError();
+
+  // SeqAnalysis.LoopSeqSize exists mostly to handle dependent contexts,
+  // otherwise it must be the same as SeqAnalysis.Loops.size().
+  assert(SeqAnalysis.LoopSeqSize == SeqAnalysis.Loops.size());
+
+  // Handle clauses, which can be any of the following: [looprange, apply]
+  const OMPLoopRangeClause *LRC =
----------------
alexey-bataev wrote:

```suggestion
  const auto *LRC =
```

https://github.com/llvm/llvm-project/pull/139293