[flang-commits] [PATCH] D154418: [flang][hlfir] avoid useless LHS temporaries inside WHERE

[Jean Perier via Phabricator via flang-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rGe52a6d7784ad: [flang][hlfir] avoid useless LHS temporaries inside WHERE (authored by jeanPerier).

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D154418/new/

https://reviews.llvm.org/D154418

Files:
  flang/lib/Optimizer/HLFIR/Transforms/ScheduleOrderedAssignments.cpp
  flang/test/HLFIR/order_assignments/where-scheduling.f90


Index: flang/test/HLFIR/order_assignments/where-scheduling.f90
===================================================================
--- flang/test/HLFIR/order_assignments/where-scheduling.f90
+++ flang/test/HLFIR/order_assignments/where-scheduling.f90
@@ -82,6 +82,27 @@
   end forall
 end subroutine
 
+subroutine no_need_to_make_lhs_temp(x, y, i, j)
+  integer :: j, i, x(:, :), y(:, :)
+  call internal
+contains
+subroutine internal
+  ! The internal procedure context currently gives a hard time to
+  ! FIR alias analysis that flags the read of i,j and y as conflicting
+  ! with the write to x. But this is not a reason to create a temporary
+  ! storage for the LHS: the address is anyway fully computed in
+  ! a descriptor (fir.box) before assigning any element of x.
+
+  ! Note that the where mask is also saved while there is no real
+  ! need to: it is addressing x elements in the same order as they
+  ! are being assigned. But this will require more work in the
+  ! conflict analysis to prove that the lowered DAG of `x(:, y(i, j))`
+  ! are the same and that the access to this designator is done in the
+  ! same ordered inside the mask and LHS.
+  where (x(:, y(i, j)) == y(i, j))  x(:, y(i, j)) = 42
+end subroutine
+end subroutine
+
 !CHECK-LABEL: ------------ scheduling where in _QPno_conflict ------------
 !CHECK-NEXT: run 1 evaluate: where/region_assign1
 !CHECK-LABEL: ------------ scheduling where in _QPfake_conflict ------------
@@ -126,3 +147,7 @@
 !CHECK-NEXT: conflict: R/W: <block argument> of type '!fir.box<!fir.array<?x?xf32>>' at index: 0 W:<block argument> of type '!fir.box<!fir.array<?x?xf32>>' at index: 0
 !CHECK-NEXT: run 1 save    : forall/where1/region_assign1/rhs
 !CHECK-NEXT: run 2 evaluate: forall/where1/region_assign1
+!CHECK-LABEL: ------------ scheduling where in _QFno_need_to_make_lhs_tempPinternal ------------
+!CHECK-NEXT: conflict: R/W: %7 = fir.load %6 : !fir.llvm_ptr<!fir.ref<i32>> W:%13 = fir.load %12 : !fir.ref<!fir.box<!fir.array<?x?xi32>>>
+!CHECK-NEXT: run 1 save    : where/mask
+!CHECK-NEXT: run 2 evaluate: where/region_assign1
Index: flang/lib/Optimizer/HLFIR/Transforms/ScheduleOrderedAssignments.cpp
===================================================================
--- flang/lib/Optimizer/HLFIR/Transforms/ScheduleOrderedAssignments.cpp
+++ flang/lib/Optimizer/HLFIR/Transforms/ScheduleOrderedAssignments.cpp
@@ -544,9 +544,15 @@
     scheduler.startIndependentEvaluationGroup();
     scheduler.saveEvaluationIfConflict(assign.getRhsRegion(),
                                        leafRegionsMayOnlyRead);
-    scheduler.saveEvaluationIfConflict(assign.getLhsRegion(),
-                                       leafRegionsMayOnlyRead,
-                                       /*yieldIsImplicitRead=*/false);
+    // There is no point to save the LHS outside of Forall and assignment to a
+    // vector subscripted LHS because the LHS is already fully evaluated and
+    // saved in the resulting SSA address value (that may be a descriptor or
+    // descriptor address).
+    if (mlir::isa<hlfir::ForallOp>(root.getOperation()) ||
+        mlir::isa<hlfir::ElementalAddrOp>(assign.getLhsRegion().back().back()))
+      scheduler.saveEvaluationIfConflict(assign.getLhsRegion(),
+                                         leafRegionsMayOnlyRead,
+                                         /*yieldIsImplicitRead=*/false);
     scheduler.finishIndependentEvaluationGroup();
     scheduler.finishSchedulingAssignment(assign);
   }


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