[flang-commits] [flang] [Flang] Add FIR and LLVM lowering support for prefetch directive (PR #167272)

[Thirumalai Shaktivel via flang-commits]

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+! Test lowering of prefetch directive
+! RUN: %flang_fc1 -emit-hlfir -o - %s | FileCheck %s --check-prefixes=HLFIR
+
+module test_prefetch_mod
+  implicit none
+  type :: t
+    integer :: a(256, 256)
+  end type t
+end module test_prefetch_mod
+
+subroutine test_prefetch_01()
+  ! HLFIR: %[[H_A:.*]]:2 = hlfir.declare {{.*}} {uniq_name = "_QFtest_prefetch_01Ea"} : (!fir.ref<!fir.array<256xi32>>, !fir.shape<1>) -> (!fir.ref<!fir.array<256xi32>>, !fir.ref<!fir.array<256xi32>>)
+  ! HLFIR: %[[H_I:.*]]:2 = hlfir.declare {{.*}} {uniq_name = "_QFtest_prefetch_01Ei"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
+  ! HLFIR: %[[H_J:.*]]:2 = hlfir.declare {{.*}} {uniq_name = "_QFtest_prefetch_01Ej"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
+
+  integer :: i, j
+  integer :: a(256)
+
+  a = 23
+
+  ! HLFIR: fir.prefetch %[[H_A]]#0 {cacheType = 1 : i32, localityHint = 3 : i32, rw = 0 : i32} : !fir.ref<!fir.array<256xi32>>
+  !dir$ prefetch a
+  i = sum(a)
+
+  ! HLFIR: %[[H_LOAD:.*]] = fir.load %[[H_I]]#0 : !fir.ref<i32>
+  ! HLFIR: %[[H_C64:.*]] = arith.constant 64 : i32
+  ! HLFIR: %[[H_ADD:.*]] = arith.addi %[[H_LOAD]], %[[H_C64]] overflow<nsw> : i32
+  ! HLFIR: %[[H_CON:.*]] = fir.convert %[[H_ADD]] : (i32) -> i64
+  ! HLFIR: %[[H_DESIG:.*]] = hlfir.designate %[[H_A]]#0 (%[[H_CON]])  : (!fir.ref<!fir.array<256xi32>>, i64) -> !fir.ref<i32>
+
+  ! HLFIR: fir.prefetch %[[H_DESIG]] {cacheType = 1 : i32, localityHint = 3 : i32, rw = 0 : i32} : !fir.ref<i32>
+  ! HLFIR: fir.prefetch %[[H_J]]#0 {cacheType = 1 : i32, localityHint = 3 : i32, rw = 0 : i32} : !fir.ref<i32>
+
+  do i = 1, (256 - 64)
+    !dir$ prefetch a(i+64), j
+    a(i) = a(i-32) + a(i+32) + j
+  end do
+end subroutine test_prefetch_01
+
+subroutine test_prefetch_02(t1)
+  use test_prefetch_mod
+  ! HLFIR: %[[H_A:.*]]:2 = hlfir.declare {{.*}} {fortran_attrs = #fir.var_attrs<allocatable>, uniq_name = "_QFtest_prefetch_02Ea"}
+  ! HLFIR: %[[H_ARG0:.*]]:2 = hlfir.declare {{.*}} dummy_scope {{.*}} {fortran_attrs = #fir.var_attrs<intent_inout>, uniq_name = "_QFtest_prefetch_02Et1"}
+  type(t), intent(inout) :: t1
+  integer, allocatable :: a(:, :)
+
+  ! HLFIR: %[[H_DESIG_01:.*]] = hlfir.designate %[[H_ARG0]]#0{"a"}   shape {{.*}}
+  ! HLFIR: fir.prefetch %[[H_DESIG_01]] {cacheType = 1 : i32, localityHint = 3 : i32, rw = 0 : i32} : !fir.ref<!fir.array<256x256xi32>>
+  !dir$ prefetch t1%a
+  a = t1%a ** 2
+
+  do i = 1, 256
+    ! HLFIR: fir.prefetch %[[H_A]]#0 {cacheType = 1 : i32, localityHint = 3 : i32, rw = 0 : i32} : !fir.ref<!fir.box<!fir.heap<!fir.array<?x?xi32>>>>
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Thirumalai-Shaktivel wrote:

I took the following example:
```
program test
integer, allocatable :: x(:)

! allocate(x(3))
!dir$ prefetch x
x = x + 1

print *, x
end program
```

This works fine without any issues. There is no crash. But if you access the element in the assignment, it causes a segmentation fault, as the array is not allocated.

https://github.com/llvm/llvm-project/pull/167272