[OpenMP] Fixed a crash when offloading to x86_64 with target nowait

PR#49334 reports a crash when offloading to x86_64 with `target nowait`,
which is caused by referencing a nullptr. The root cause of the issue is, when
pushing a hidden helper task in `__kmp_push_task`, it also maps the gtid to its
shadow gtid, which is wrong.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D97329

(cherry picked from commit e5da63d5a9ede1fb6d8aa18cfd44533ead128738)

2 files changed, 150 insertions, 1 deletions

diff --git a/openmp/libomptarget/test/offloading/bug49334.cpp b/openmp/libomptarget/test/offloading/bug49334.cpp
new file mode 100644
index 0000000..b26cd7b
--- /dev/null
+++ b/openmp/libomptarget/test/offloading/bug49334.cpp
@@ -0,0 +1,148 @@
+// RUN: %libomptarget-compilexx-run-and-check-aarch64-unknown-linux-gnu
+// RUN: %libomptarget-compilexx-run-and-check-powerpc64-ibm-linux-gnu
+// RUN: %libomptarget-compilexx-run-and-check-powerpc64le-ibm-linux-gnu
+// RUN: %libomptarget-compilexx-run-and-check-x86_64-pc-linux-gnu
+// RUN: %libomptarget-compilexx-run-and-check-nvptx64-nvidia-cuda
+
+#include <cassert>
+#include <iostream>
+#include <memory>
+#include <vector>
+
+class BlockMatrix {
+private:
+  const int rowsPerBlock;
+  const int colsPerBlock;
+  const long nRows;
+  const long nCols;
+  const int nBlocksPerRow;
+  const int nBlocksPerCol;
+  std::vector<std::vector<std::unique_ptr<float[]>>> Blocks;
+
+public:
+  BlockMatrix(const int _rowsPerBlock, const int _colsPerBlock,
+              const long _nRows, const long _nCols)
+      : rowsPerBlock(_rowsPerBlock), colsPerBlock(_colsPerBlock), nRows(_nRows),
+        nCols(_nCols), nBlocksPerRow(_nRows / _rowsPerBlock),
+        nBlocksPerCol(_nCols / _colsPerBlock), Blocks(nBlocksPerCol) {
+    for (int i = 0; i < nBlocksPerCol; i++) {
+      for (int j = 0; j < nBlocksPerRow; j++) {
+        Blocks[i].emplace_back(new float[_rowsPerBlock * _colsPerBlock]);
+      }
+    }
+  };
+
+  // Initialize the BlockMatrix from 2D arrays
+  void Initialize(const std::vector<float> &matrix) {
+    for (int i = 0; i < nBlocksPerCol; i++)
+      for (int j = 0; j < nBlocksPerRow; j++) {
+        float *CurrBlock = GetBlock(i, j);
+        for (int ii = 0; ii < colsPerBlock; ++ii)
+          for (int jj = 0; jj < rowsPerBlock; ++jj) {
+            int curri = i * colsPerBlock + ii;
+            int currj = j * rowsPerBlock + jj;
+            CurrBlock[ii + jj * colsPerBlock] = matrix[curri + currj * nCols];
+          }
+      }
+  }
+
+  long Compare(const std::vector<float> &matrix) const {
+    long fail = 0;
+    for (int i = 0; i < nBlocksPerCol; i++)
+      for (int j = 0; j < nBlocksPerRow; j++) {
+        float *CurrBlock = GetBlock(i, j);
+        for (int ii = 0; ii < colsPerBlock; ++ii)
+          for (int jj = 0; jj < rowsPerBlock; ++jj) {
+            int curri = i * colsPerBlock + ii;
+            int currj = j * rowsPerBlock + jj;
+            float m_value = matrix[curri + currj * nCols];
+            float bm_value = CurrBlock[ii + jj * colsPerBlock];
+            if (bm_value != m_value) {
+              fail++;
+            }
+          }
+      }
+    return fail;
+  }
+
+  float *GetBlock(int i, int j) const {
+    assert(i < nBlocksPerCol && j < nBlocksPerRow && "Accessing outside block");
+    return Blocks[i][j].get();
+  }
+};
+
+constexpr const int BS = 256;
+constexpr const int N = 1024;
+
+int BlockMatMul_TargetNowait(BlockMatrix &A, BlockMatrix &B, BlockMatrix &C) {
+#pragma omp parallel
+#pragma omp master
+  for (int i = 0; i < N / BS; ++i)
+    for (int j = 0; j < N / BS; ++j) {
+      float *BlockC = C.GetBlock(i, j);
+      for (int k = 0; k < N / BS; ++k) {
+        float *BlockA = A.GetBlock(i, k);
+        float *BlockB = B.GetBlock(k, j);
+// clang-format off
+#pragma omp target depend(in: BlockA[0], BlockB[0]) depend(inout: BlockC[0])   \
+            map(to: BlockA[:BS * BS], BlockB[:BS * BS])                        \
+            map(tofrom: BlockC[:BS * BS]) nowait
+// clang-format on
+#pragma omp parallel for
+        for (int ii = 0; ii < BS; ii++)
+          for (int jj = 0; jj < BS; jj++) {
+            for (int kk = 0; kk < BS; ++kk)
+              BlockC[ii + jj * BS] +=
+                  BlockA[ii + kk * BS] * BlockB[kk + jj * BS];
+          }
+      }
+    }
+  return 0;
+}
+
+void Matmul(const std::vector<float> &a, const std::vector<float> &b,
+            std::vector<float> &c) {
+  for (int i = 0; i < N; ++i) {
+    for (int j = 0; j < N; ++j) {
+      float sum = 0.0;
+      for (int k = 0; k < N; ++k) {
+        sum = sum + a[i * N + k] * b[k * N + j];
+      }
+      c[i * N + j] = sum;
+    }
+  }
+}
+
+int main(int argc, char *argv[]) {
+  std::vector<float> a(N * N);
+  std::vector<float> b(N * N);
+  std::vector<float> c(N * N, 0.0);
+
+  for (int i = 0; i < N; ++i) {
+    for (int j = 0; j < N; ++j) {
+      a[i * N + j] = b[i * N + j] = i + j % 100;
+    }
+  }
+
+  auto BlockedA = BlockMatrix(BS, BS, N, N);
+  BlockedA.Initialize(a);
+  BlockedA.Compare(a);
+  auto BlockedB = BlockMatrix(BS, BS, N, N);
+  BlockedB.Initialize(b);
+  BlockedB.Compare(b);
+
+  Matmul(a, b, c);
+
+  auto BlockedC = BlockMatrix(BS, BS, N, N);
+  BlockMatMul_TargetNowait(BlockedA, BlockedB, BlockedC);
+
+  if (BlockedC.Compare(c) > 0) {
+    return 1;
+  }
+
+  std::cout << "PASS\n";
+
+  return 0;
+}
+
+// CHECK: PASS
diff --git a/openmp/runtime/src/kmp_tasking.cpp b/openmp/runtime/src/kmp_tasking.cpp
index 3d70211..4bcd119 100644
--- a/openmp/runtime/src/kmp_tasking.cpp
+++ b/openmp/runtime/src/kmp_tasking.cpp
@@ -326,7 +326,8 @@ static kmp_int32 __kmp_push_task(kmp_int32 gtid, kmp_task_t *task) {
   kmp_info_t *thread = __kmp_threads[gtid];
   kmp_taskdata_t *taskdata = KMP_TASK_TO_TASKDATA(task);
 
-  if (taskdata->td_flags.hidden_helper) {
+  // We don't need to map to shadow gtid if it is already hidden helper thread
+  if (taskdata->td_flags.hidden_helper && !KMP_HIDDEN_HELPER_THREAD(gtid)) {
     gtid = KMP_GTID_TO_SHADOW_GTID(gtid);
     thread = __kmp_threads[gtid];
   }