Revert "[OpenMP][OpenMPIRBuilder] Implement loop unrolling."

Breaks build with -DBUILD_SHARED_LIBS=ON
```
CMake Error: The inter-target dependency graph contains the following strongly connected component (cycle):
  "LLVMFrontendOpenMP" of type SHARED_LIBRARY
    depends on "LLVMPasses" (weak)
  "LLVMipo" of type SHARED_LIBRARY
    depends on "LLVMFrontendOpenMP" (weak)
  "LLVMCoroutines" of type SHARED_LIBRARY
    depends on "LLVMipo" (weak)
  "LLVMPasses" of type SHARED_LIBRARY
    depends on "LLVMCoroutines" (weak)
    depends on "LLVMipo" (weak)
At least one of these targets is not a STATIC_LIBRARY.  Cyclic dependencies are allowed only among static libraries.
CMake Generate step failed.  Build files cannot be regenerated correctly.
```

This reverts commit 707ce34b06190e275572c3c46843036db1bab6d1.

Author: LebedevRI

clang/include/clang/Sema/Sema.h

@@ -10572,11 +10572,6 @@ class Sema final {
   /// an OpenMP loop directive.
   StmtResult ActOnOpenMPCanonicalLoop(Stmt *AStmt);
 
-  /// Process a canonical OpenMP loop nest that can either be a canonical
-  /// literal loop (ForStmt or CXXForRangeStmt), or the generated loop of an
-  /// OpenMP loop transformation construct.
-  StmtResult ActOnOpenMPLoopnest(Stmt *AStmt);
-
   /// End of OpenMP region.
   ///
   /// \param S Statement associated with the current OpenMP region.

clang/lib/CodeGen/CGStmtOpenMP.cpp

@@ -1951,27 +1951,11 @@ llvm::CanonicalLoopInfo *
 CodeGenFunction::EmitOMPCollapsedCanonicalLoopNest(const Stmt *S, int Depth) {
   assert(Depth == 1 && "Nested loops with OpenMPIRBuilder not yet implemented");
 
-  // The caller is processing the loop-associated directive processing the \p
-  // Depth loops nested in \p S. Put the previous pending loop-associated
-  // directive to the stack. If the current loop-associated directive is a loop
-  // transformation directive, it will push its generated loops onto the stack
-  // such that together with the loops left here they form the combined loop
-  // nest for the parent loop-associated directive.
-  int ParentExpectedOMPLoopDepth = ExpectedOMPLoopDepth;
-  ExpectedOMPLoopDepth = Depth;
-
   EmitStmt(S);
   assert(OMPLoopNestStack.size() >= (size_t)Depth && "Found too few loops");
 
   // The last added loop is the outermost one.
-  llvm::CanonicalLoopInfo *Result = OMPLoopNestStack.back();
-
-  // Pop the \p Depth loops requested by the call from that stack and restore
-  // the previous context.
-  OMPLoopNestStack.set_size(OMPLoopNestStack.size() - Depth);
-  ExpectedOMPLoopDepth = ParentExpectedOMPLoopDepth;
-
-  return Result;
+  return OMPLoopNestStack.back();
 }
 
 void CodeGenFunction::EmitOMPCanonicalLoop(const OMPCanonicalLoop *S) {
@@ -2601,46 +2585,6 @@ void CodeGenFunction::EmitOMPTileDirective(const OMPTileDirective &S) {
 }
 
 void CodeGenFunction::EmitOMPUnrollDirective(const OMPUnrollDirective &S) {
-  bool UseOMPIRBuilder = CGM.getLangOpts().OpenMPIRBuilder;
-
-  if (UseOMPIRBuilder) {
-    auto DL = SourceLocToDebugLoc(S.getBeginLoc());
-    const Stmt *Inner = S.getRawStmt();
-
-    // Consume nested loop. Clear the entire remaining loop stack because a
-    // fully unrolled loop is non-transformable. For partial unrolling the
-    // generated outer loop is pushed back to the stack.
-    llvm::CanonicalLoopInfo *CLI = EmitOMPCollapsedCanonicalLoopNest(Inner, 1);
-    OMPLoopNestStack.clear();
-
-    llvm::OpenMPIRBuilder &OMPBuilder = CGM.getOpenMPRuntime().getOMPBuilder();
-
-    bool NeedsUnrolledCLI = ExpectedOMPLoopDepth >= 1;
-    llvm::CanonicalLoopInfo *UnrolledCLI = nullptr;
-
-    if (S.hasClausesOfKind<OMPFullClause>()) {
-      assert(ExpectedOMPLoopDepth == 0);
-      OMPBuilder.unrollLoopFull(DL, CLI);
-    } else if (auto *PartialClause = S.getSingleClause<OMPPartialClause>()) {
-      uint64_t Factor = 0;
-      if (Expr *FactorExpr = PartialClause->getFactor()) {
-        Factor = FactorExpr->EvaluateKnownConstInt(getContext()).getZExtValue();
-        assert(Factor >= 1 && "Only positive factors are valid");
-      }
-      OMPBuilder.unrollLoopPartial(DL, CLI, Factor,
-                                   NeedsUnrolledCLI ? &UnrolledCLI : nullptr);
-    } else {
-      OMPBuilder.unrollLoopHeuristic(DL, CLI);
-    }
-
-    assert((!NeedsUnrolledCLI || UnrolledCLI) &&
-           "NeedsUnrolledCLI implies UnrolledCLI to be set");
-    if (UnrolledCLI)
-      OMPLoopNestStack.push_back(UnrolledCLI);
-
-    return;
-  }
-
   // This function is only called if the unrolled loop is not consumed by any
   // other loop-associated construct. Such a loop-associated construct will have
   // used the transformed AST.

clang/lib/CodeGen/CodeGenFunction.h

@@ -291,10 +291,6 @@ class CodeGenFunction : public CodeGenTypeCache {
   /// nest would extend.
   SmallVector<llvm::CanonicalLoopInfo *, 4> OMPLoopNestStack;
 
-  /// Number of nested loop to be consumed by the last surrounding
-  /// loop-associated directive.
-  int ExpectedOMPLoopDepth = 0;
-
   // CodeGen lambda for loops and support for ordered clause
   typedef llvm::function_ref<void(CodeGenFunction &, const OMPLoopDirective &,
                                   JumpDest)>

clang/lib/Parse/ParseOpenMP.cpp

@@ -2562,7 +2562,8 @@ Parser::ParseOpenMPDeclarativeOrExecutableDirective(ParsedStmtContext StmtCtx) {
 
         if (AssociatedStmt.isUsable() && isOpenMPLoopDirective(DKind) &&
             getLangOpts().OpenMPIRBuilder)
-          AssociatedStmt = Actions.ActOnOpenMPLoopnest(AssociatedStmt.get());
+          AssociatedStmt =
+              Actions.ActOnOpenMPCanonicalLoop(AssociatedStmt.get());
       }
       AssociatedStmt = Actions.ActOnOpenMPRegionEnd(AssociatedStmt, Clauses);
     } else if (DKind == OMPD_target_update || DKind == OMPD_target_enter_data ||

clang/lib/Sema/SemaOpenMP.cpp

@@ -5573,19 +5573,6 @@ StmtResult Sema::ActOnOpenMPCanonicalLoop(Stmt *AStmt) {
                                   LoopVarFunc, LVRef);
 }
 
-StmtResult Sema::ActOnOpenMPLoopnest(Stmt *AStmt) {
-  // Handle a literal loop.
-  if (isa<ForStmt>(AStmt) || isa<CXXForRangeStmt>(AStmt))
-    return ActOnOpenMPCanonicalLoop(AStmt);
-
-  // If not a literal loop, it must be the result of a loop transformation.
-  OMPExecutableDirective *LoopTransform = cast<OMPExecutableDirective>(AStmt);
-  assert(
-      isOpenMPLoopTransformationDirective(LoopTransform->getDirectiveKind()) &&
-      "Loop transformation directive expected");
-  return LoopTransform;
-}
-
 static ExprResult buildUserDefinedMapperRef(Sema &SemaRef, Scope *S,
                                             CXXScopeSpec &MapperIdScopeSpec,
                                             const DeclarationNameInfo &MapperId,