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

[Anchu Rajendran S via llvm-commits]

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@@ -3774,6 +3900,84 @@ class CanonicalLoopInfo {
   LLVM_ABI void invalidate();
 };
 
+/// ScanInfo holds the information to assist in lowering of Scan reduction.
+/// Before lowering, body of the for loop specifying scan reduction is expected
+/// to have the following structure
+///     Loop Body Entry
+///        |
+///     Code before the scan directive
+///        |
+///     Scan Directive
+///        |
+///     Code after the scan directive
+///        |
+///     Loop Body Exit
+/// When `createCanonicalScanLoops` is executed, the bodyGen callback of it
+/// transforms the body to:
+///
+///     Loop Body Entry
+///        |
+///     OMPScanDispatch
+///
+///     OMPBeforeScanBlock
+///        |
+///     OMPScanLoopExit
+///        |
+///     Loop Body Exit
+///
+/// The insert point is updated to the first insert point of OMPBeforeScanBlock.
+/// It dominates the control flow of code generated until
+/// scan directive is encountered and OMPAfterScanBlock dominates the
+/// control flow of code generated after scan is encountered. The successor
+/// of OMPScanDispatch can be OMPBeforeScanBlock or OMPAfterScanBlock based
+/// on 1.whether it is in Input phase or Scan Phase , 2. whether it is an
+/// exclusive or inclusive scan. This jump is added when `createScan` is
+/// executed. If input loop is being generated, if it is inclusive scan,
+/// `OMPAfterScanBlock` succeeds `OMPScanDispatch` , if exclusive,
+/// `OMPBeforeScanBlock` succeeds `OMPDispatch` and vice versa for scan loop. At
+/// the end of the input loop, temporary buffer is populated and at the
+/// beginning of the scan loop, temporary buffer is read. After scan directive
+/// is encountered, insertion point is updated to `OMPAfterScanBlock` as it is
+/// expected to dominate the code after the scan directive. Both Before and
+/// After scan blocks are succeeded by `OMPScanLoopExit`.
+/// Temporary buffer allocations are done in `ScanLoopInit` block before the
+/// lowering of for-loop. The results are copied back to reduction variable in
+/// `ScanLoopFinish` block.
+
+class ScanInfo {
+public:
+  /// Dominates the body of the loop before scan directive
+  llvm::BasicBlock *OMPBeforeScanBlock = nullptr;
+  /// Dominates the body of the loop before scan directive
+  llvm::BasicBlock *OMPAfterScanBlock = nullptr;
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anchuraj wrote:

Updated

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