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[flang] Do not re-localize loop ivs when nested inside blocks (#153350)

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Consider the following example:
```fortran
  implicit none
  integer :: i, j

  do concurrent (i=1:10) local(j)
    block
      do j=1,20
      end do
    end block
  end do
```

Without the fix introduced in this PR, the compiler would "re-localize"
the `j` variable inside the `fir.do_concurrent` loop:
```mlir
    fir.do_concurrent {
      %7 = fir.alloca i32 {bindc_name = "j"}
      %8:2 = hlfir.declare %7 {uniq_name = "_QFloop_in_nested_blockEj"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
      ...
      fir.do_concurrent.loop (%arg0) = (%5) to (%6) step (%c1) local(@_QFloop_in_nested_blockEj_private_i32 %4#0 -> %arg1 : !fir.ref<i32>) {
        %12:2 = hlfir.declare %arg1 {uniq_name = "_QFloop_in_nested_blockEj"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
        ...
        %17:2 = fir.do_loop %arg2 = %14 to %15 step %c1_1 iter_args(%arg3 = %16) -> (index, i32) {
          fir.store %arg3 to %8#0 : !fir.ref<i32>
          ...
        }
      }
    }
```

This happened because we did a shallow look-up of `j` and since the loop
is nested inside a `block`, the look-up failed and we re-created a local
allocation for `j` inside the parent `fir.do_concurrent` loop. This
means that we ended up not using the actual localized symbol which is
passed as a region argument to the `fir.do_concurrent.loop` op.

In case of `j`, we do not need to do a shallow look-up. The shallow
look-up is only needed if a symbol is an OpenMP private one or an
iteration variable of a `do concurrent` loop. Neither of which applies
to `j`.

With the fix, `j` is properly resolved to the `local` region argument:
```mlir
    fir.do_concurrent {
      ...
      fir.do_concurrent.loop (%arg0) = (%5) to (%6) step (%c1) local(@_QFloop_in_nested_blockEj_private_i32 %4#0 -> %arg1 : !fir.ref<i32>) {
        ...
        %10:2 = hlfir.declare %arg1 {uniq_name = "_QFloop_in_nested_blockEj"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
        ...
        %15:2 = fir.do_loop %arg2 = %12 to %13 step %c1_1 iter_args(%arg3 = %14) -> (index, i32) {
          fir.store %arg3 to %10#0 : !fir.ref<i32>
          ...
        }
      }
    }
```
This commit is contained in:
Kareem Ergawy 2025-08-15 08:45:02 +02:00 committed by GitHub
parent e2eaea412a
commit b9e33fd493
No known key found for this signature in database
GPG Key ID: B5690EEEBB952194
2 changed files with 43 additions and 15 deletions
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32
flang/lib/Lower/Bridge.cpp
View File

@ -1400,21 +1400,23 @@ private:
mlir::Value genLoopVariableAddress(mlir::Location loc,
const Fortran::semantics::Symbol &sym,
bool isUnordered) {
if (isUnordered || sym.has<Fortran::semantics::HostAssocDetails>() ||
sym.has<Fortran::semantics::UseDetails>()) {
if (!shallowLookupSymbol(sym) &&
!GetSymbolDSA(sym).test(
Fortran::semantics::Symbol::Flag::OmpShared)) {
// Do concurrent loop variables are not mapped yet since they are local
// to the Do concurrent scope (same for OpenMP loops).
mlir::OpBuilder::InsertPoint insPt = builder->saveInsertionPoint();
builder->setInsertionPointToStart(builder->getAllocaBlock());
mlir::Type tempTy = genType(sym);
mlir::Value temp =
builder->createTemporaryAlloc(loc, tempTy, toStringRef(sym.name()));
bindIfNewSymbol(sym, temp);
builder->restoreInsertionPoint(insPt);
}
if (!shallowLookupSymbol(sym) &&
(isUnordered ||
GetSymbolDSA(sym).test(Fortran::semantics::Symbol::Flag::OmpPrivate) ||
GetSymbolDSA(sym).test(
Fortran::semantics::Symbol::Flag::OmpFirstPrivate) ||
GetSymbolDSA(sym).test(
Fortran::semantics::Symbol::Flag::OmpLastPrivate) ||
GetSymbolDSA(sym).test(Fortran::semantics::Symbol::Flag::OmpLinear))) {
// Do concurrent loop variables are not mapped yet since they are
// local to the Do concurrent scope (same for OpenMP loops).
mlir::OpBuilder::InsertPoint insPt = builder->saveInsertionPoint();
builder->setInsertionPointToStart(builder->getAllocaBlock());
mlir::Type tempTy = genType(sym);
mlir::Value temp =
builder->createTemporaryAlloc(loc, tempTy, toStringRef(sym.name()));
bindIfNewSymbol(sym, temp);
builder->restoreInsertionPoint(insPt);
}
auto entry = lookupSymbol(sym);
(void)entry;

26
flang/test/Lower/do_concurrent_loop_in_nested_block.f90 Normal file
View File

@ -0,0 +1,26 @@
! RUN: %flang_fc1 -emit-hlfir -mmlir --enable-delayed-privatization-staging=true -o - %s | FileCheck %s
subroutine loop_in_nested_block
implicit none
integer :: i, j
do concurrent (i=1:10) local(j)
block
do j=1,20
end do
end block
end do
end subroutine
! CHECK-LABEL: func.func @_QPloop_in_nested_block() {
! CHECK: %[[OUTER_J_DECL:.*]]:2 = hlfir.declare %{{.*}} {uniq_name = "{{.*}}Ej"}
! CHECK: fir.do_concurrent {
! CHECK: fir.do_concurrent.loop {{.*}} local(@{{.*}} %[[OUTER_J_DECL]]#0 -> %[[LOCAL_J_ARG:.*]] : !fir.ref<i32>) {
! CHECK: %[[LOCAL_J_DECL:.*]]:2 = hlfir.declare %[[LOCAL_J_ARG]]
! CHECK: fir.do_loop {{.*}} iter_args(%[[NESTED_LOOP_ARG:.*]] = {{.*}}) {
! CHECK: fir.store %[[NESTED_LOOP_ARG]] to %[[LOCAL_J_DECL]]#0
! CHECK: }
! CHECK: }
! CHECK: }
! CHECK: }