[OpenMP][OMPIRBuilder] Fix LLVM IR codegen for collapsed device loop (#78708)

When we generate the loop body function, we need to be sure, that all
original loop counters are replaced by the new counter.

We need to save all items which use the original loop counter and then
perform replacement of the original loop counter. If we don't do it,
there is a risk that some values are not updated.

Author: DominikAdamski

llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp

@@ -2876,9 +2876,10 @@ OpenMPIRBuilder::applyWorkshareLoopTarget(DebugLoc DL, CanonicalLoopInfo *CLI,
   // We need to model loop body region as the function f(cnt, loop_arg).
   // That's why we replace loop induction variable by the new counter
   // which will be one of loop body function argument
-  for (auto Use = CLI->getIndVar()->user_begin();
-       Use != CLI->getIndVar()->user_end(); ++Use) {
-    if (Instruction *Inst = dyn_cast<Instruction>(*Use)) {
+  SmallVector<User *> Users(CLI->getIndVar()->user_begin(),
+                            CLI->getIndVar()->user_end());
+  for (auto Use : Users) {
+    if (Instruction *Inst = dyn_cast<Instruction>(Use)) {
       if (ParallelRegionBlockSet.count(Inst->getParent())) {
         Inst->replaceUsesOfWith(CLI->getIndVar(), NewLoopCntLoad);
       }

mlir/test/Target/LLVMIR/omptarget-wsloop-collapsed.mlir

@@ -0,0 +1,39 @@
+// RUN: mlir-translate -mlir-to-llvmir %s | FileCheck %s
+
+// The aim of the test is to check the GPU LLVM IR codegen
+// for nested omp do loop with collapse clause inside omp target region
+
+module attributes {dlti.dl_spec = #dlti.dl_spec<#dlti.dl_entry<"dlti.alloca_memory_space", 5 : ui32>>, llvm.data_layout = "e-p:64:64-p1:64:64-p2:32:32-p3:32:32-p4:64:64-p5:32:32-p6:32:32-p7:160:256:256:32-p8:128:128-i64:64-v16:16-v24:32-v32:32-v48:64-v96:128-v192:256-v256:256-v512:512-v1024:1024-v2048:2048-n32:64-S32-A5-G1-ni:7:8", llvm.target_triple = "amdgcn-amd-amdhsa", omp.is_gpu = true, omp.is_target_device = true } {
+  llvm.func @target_collapsed_wsloop(%arg0: !llvm.ptr) {
+    %loop_ub = llvm.mlir.constant(99 : i32) : i32
+    %loop_lb = llvm.mlir.constant(0 : i32) : i32
+    %loop_step = llvm.mlir.constant(1 : index) : i32
+    omp.wsloop for  (%arg1, %arg2) : i32 = (%loop_lb, %loop_lb) to (%loop_ub, %loop_ub) inclusive step (%loop_step, %loop_step) {
+      %1 = llvm.add %arg1, %arg2  : i32
+      %2 = llvm.mul %arg2, %loop_ub overflow<nsw>  : i32
+      %3 = llvm.add %arg1, %2 :i32
+      %4 = llvm.getelementptr %arg0[%3] : (!llvm.ptr, i32) -> !llvm.ptr, i32
+      llvm.store %1, %4 : i32, !llvm.ptr
+      omp.yield
+    }
+    llvm.return
+  }
+}
+
+// CHECK: define void @[[FUNC_COLLAPSED_WSLOOP:.*]](ptr %[[ARG0:.*]])
+// CHECK:   call void @__kmpc_for_static_loop_4u(ptr addrspacecast (ptr addrspace(1) @[[GLOB2:[0-9]+]] to ptr),
+// CHECK-SAME: ptr @[[COLLAPSED_WSLOOP_BODY_FN:.*]], ptr %[[STRUCT_ARG:.*]], i32 10000,
+// CHECK-SAME: i32 %[[NUM_THREADS:.*]], i32 0)
+
+// CHECK: define internal void @[[COLLAPSED_WSLOOP_BODY_FN]](i32 %[[LOOP_CNT:.*]], ptr %[[LOOP_BODY_ARG:.*]])
+// CHECK:   %[[TMP0:.*]] = urem i32 %[[LOOP_CNT]], 100
+// CHECK:   %[[TMP1:.*]] = udiv i32 %[[LOOP_CNT]], 100
+// CHECK:   %[[TMP2:.*]] = mul i32 %[[TMP1]], 1
+// CHECK:   %[[TMP3:.*]] = add i32 %[[TMP2]], 0
+// CHECK:   %[[TMP4:.*]] = mul i32 %[[TMP0]], 1
+// CHECK:   %[[TMP5:.*]] = add i32 %[[TMP4]], 0
+// CHECK:   %[[TMP6:.*]] = add i32 %[[TMP3]], %[[TMP5]]
+// CHECK:   %[[TMP7:.*]] = mul nsw i32 %[[TMP5]], 99
+// CHECK:   %[[TMP8:.*]] = add i32 %[[TMP3]], %[[TMP7]]
+// CHECK:   %[[TMP9:.*]] = getelementptr i32, ptr %[[ARRAY:.*]], i32 %[[TMP8]]
+// CHECK:   store i32 %[[TMP6]], ptr %[[TMP9]], align 4

openmp/libomptarget/test/offloading/fortran/target-parallel-do-collapse.f90

@@ -0,0 +1,44 @@
+! Basic offloading test with a target region
+! REQUIRES: flang
+! UNSUPPORTED: nvptx64-nvidia-cuda-LTO
+! UNSUPPORTED: aarch64-unknown-linux-gnu
+! UNSUPPORTED: aarch64-unknown-linux-gnu-LTO
+! UNSUPPORTED: x86_64-pc-linux-gnu
+! UNSUPPORTED: x86_64-pc-linux-gnu-LTO
+
+! RUN: %libomptarget-compile-fortran-generic
+! RUN: env LIBOMPTARGET_INFO=16 %libomptarget-run-generic 2>&1 | %fcheck-generic
+program main
+   use omp_lib
+   implicit none
+   integer :: i,j
+   integer :: array(10,10), errors = 0
+   do i = 1, 10
+      do j = 1, 10
+         array(j, i) = 0
+      end do
+   end do
+
+   !$omp target parallel do map(from:array) collapse(2)
+   do i = 1, 10
+      do j = 1, 10
+         array( j, i) = i + j
+      end do
+    end do
+    !$omp end target parallel do
+
+    do i = 1, 10
+       do j = 1, 10
+          if ( array( j, i) .ne. (i + j) ) then
+             errors = errors + 1
+          end if
+       end do
+   end do
+
+   print *,"number of errors: ", errors
+
+end program main
+
+! CHECK:  "PluginInterface" device {{[0-9]+}} info: Launching kernel {{.*}}
+! CHECK:  number of errors: 0
+