[llvm] [OpenMP] [IR Builder] Changes to Support Scan Operation (PR #136035)

[Michael Kruse via llvm-commits]

================
@@ -2639,6 +2725,46 @@ class OpenMPIRBuilder {
                                              FinalizeCallbackTy FiniCB,
                                              Value *Filter);
 
+  /// This function performs the scan reduction of the values updated in
+  /// the input phase. The reduction logic needs to be emitted between input
+  /// and scan loop returned by `CreateCanonicalScanLoops`. The following
+  /// is the code that is generated, `buffer` and `span` are expected to be
+  /// populated before executing the generated code.
+  ///
+  ///  for (int k = 0; k != ceil(log2(span)); ++k) {
+  ///    i=pow(2,k)
+  ///    for (size cnt = last_iter; cnt >= i; --cnt)
+  ///      buffer[cnt] op= buffer[cnt-i];
+  ///  }
+  /// \param Loc The insert and source location description.
+  /// \param ReductionInfos Array type containing the ReductionOps.
+  /// \param ScanRedInfo  Pointer to the ScanInfo objected created using
+  /// `ScanInfoInitialize`.
+  ///
+  /// \returns The insertion position *after* the masked.
+  InsertPointOrErrorTy emitScanReduction(
+      const LocationDescription &Loc,
+      ArrayRef<llvm::OpenMPIRBuilder::ReductionInfo> ReductionInfos,
+      ScanInfo *ScanRedInfo);
+
+  /// This directive split and directs the control flow to input phase
+  ///  blocks or scan phase blocks based on 1. whether input loop or scan loop
+  ///  is executed, 2. whether exclusive or inclusive scan is used.
+  ///
+  /// \param Loc The insert and source location description.
+  /// \param AllocaIP The IP where the temporary buffer for scan reduction
+  //                  needs to be allocated.
+  /// \param ScanVars Scan Variables.
+  /// \param IsInclusive Whether it is an inclusive or exclusive scan.
+  /// \param ScanRedInfo  Pointer to the ScanInfo objected created using
+  /// `ScanInfoInitialize`.
+  ///
+  /// \returns The insertion position *after* the scan.
+  InsertPointOrErrorTy createScan(const LocationDescription &Loc,
+                                  InsertPointTy AllocaIP,
+                                  ArrayRef<llvm::Value *> ScanVars,
+                                  ArrayRef<llvm::Type *> ScanVarsType,
+                                  bool IsInclusive, ScanInfo *ScanRedInfo);
   /// Generator for '#omp critical'
----------------
Meinersbur wrote:

```suggestion
                                  bool IsInclusive, ScanInfo *ScanRedInfo);
                                  
  /// Generator for '#omp critical'
```
[nit] whitespace

https://github.com/llvm/llvm-project/pull/136035