6f9e688203
Replaces https://github.com/llvm/llvm-project/pull/121886 Fixes https://github.com/llvm/llvm-project/issues/120254 (hopefully 🤞) ## Problem Consider the following example: ```fortran program test real :: x(1) integer :: i !$omp parallel do reduction(+:x) do i = 1,1 x = 1 end do !$omp end parallel do end program ``` The HLFIR+OMP IR for this example looks like this: ```mlir func.func @_QQmain() { ... omp.parallel { %5 = fir.embox %4#0(%3) : (!fir.ref<!fir.array<1xf32>>, !fir.shape<1>) -> !fir.box<!fir.array<1xf32>> %6 = fir.alloca !fir.box<!fir.array<1xf32>> ... omp.wsloop private(@_QFEi_private_ref_i32 %1#0 -> %arg0 : !fir.ref<i32>) reduction(byref @add_reduction_byref_box_1xf32 %6 -> %arg1 : !fir.ref<!fir.box<!fir.array<1xf32>>>) { omp.loop_nest (%arg2) : i32 = (%c1_i32) to (%c1_i32_0) inclusive step (%c1_i32_1) { ... omp.yield } } omp.terminator } return } ``` The problem addressed by this PR is related to: the `alloca` in the `omp.parallel` region + the related `reduction` clause on the `omp.wsloop` op. When we try translate the reduction from MLIR to LLVM, we have to choose an `alloca` insertion point. This happens in `convertOmpWsloop` where at entry to that function, this is what the LLVM module looks like: ```llvm define void @_QQmain() { %tid.addr = alloca i32, align 4 ... entry: %omp_global_thread_num = call i32 @__kmpc_global_thread_num(ptr @1) br label %omp.par.entry omp.par.entry: %tid.addr.local = alloca i32, align 4 ... br label %omp.par.region omp.par.region: br label %omp.par.region1 omp.par.region1: ... %5 = alloca { ptr, i64, i32, i8, i8, i8, i8, [1 x [3 x i64]] }, align 8 ``` Now, when we choose an `alloca` insertion point for the reduction, this is the chosen block `omp.par.entry` (without the changes in this PR). The problem is that the allocation needed for the reduction needs to reference the `%5` SSA value. This results in inserting allocations in `omp.par.entry` that reference allocations in a later block `omp.par.region1` which causes the `Instruction does not dominate all uses!` error. ## Possible solution - take 2: This PR contains a more localized solution than https://github.com/llvm/llvm-project/pull/121886. It makes sure that on entry to `initReductionVars`, the IR builder is at a point where we can starting inserting initialization region; to make things cleaner, we still split the builder insertion point to a dedicated `omp.reduction.init`. This way we avoid splitting after the latest allocation block; which is what causing the issue.
Flang Integration Tests
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