[llvm-branch-commits] [flang] [Flang][OpenMP] Allow host evaluation of loop bounds for distribute (PR #127822)

[Sergio Afonso via llvm-branch-commits]

https://github.com/skatrak updated https://github.com/llvm/llvm-project/pull/127822

>From 25e308a580946e40e4d74aae7f04d570723bb267 Mon Sep 17 00:00:00 2001
From: Sergio Afonso <safonsof at amd.com>
Date: Wed, 19 Feb 2025 15:15:01 +0000
Subject: [PATCH] [Flang][OpenMP] Allow host evaluation of loop bounds for
 distribute

This patch adds `target teams distribute [simd]` and equivalent construct nests
to the list of cases where loop bounds can be evaluated in the host, as they
represent Generic-SPMD kernels for which the trip count must also be evaluated
in advance to the kernel call.
---
 flang/lib/Lower/OpenMP/OpenMP.cpp     |  12 +--
 flang/test/Lower/OpenMP/host-eval.f90 | 103 ++++++++++++++++++++++++++
 2 files changed, 110 insertions(+), 5 deletions(-)

diff --git a/flang/lib/Lower/OpenMP/OpenMP.cpp b/flang/lib/Lower/OpenMP/OpenMP.cpp
index bd794033cdf11..8c80453610473 100644
--- a/flang/lib/Lower/OpenMP/OpenMP.cpp
+++ b/flang/lib/Lower/OpenMP/OpenMP.cpp
@@ -562,8 +562,11 @@ static void processHostEvalClauses(lower::AbstractConverter &converter,
       [[fallthrough]];
     case OMPD_distribute_parallel_do:
     case OMPD_distribute_parallel_do_simd:
-      cp.processCollapse(loc, eval, hostInfo.ops, hostInfo.iv);
       cp.processNumThreads(stmtCtx, hostInfo.ops);
+      [[fallthrough]];
+    case OMPD_distribute:
+    case OMPD_distribute_simd:
+      cp.processCollapse(loc, eval, hostInfo.ops, hostInfo.iv);
       break;
 
     // Cases where 'teams' clauses might be present, and target SPMD is
@@ -573,10 +576,8 @@ static void processHostEvalClauses(lower::AbstractConverter &converter,
       [[fallthrough]];
     case OMPD_target_teams:
       cp.processNumTeams(stmtCtx, hostInfo.ops);
-      processSingleNestedIf([](Directive nestedDir) {
-        return nestedDir == OMPD_distribute_parallel_do ||
-               nestedDir == OMPD_distribute_parallel_do_simd;
-      });
+      processSingleNestedIf(
+          [](Directive nestedDir) { return topDistributeSet.test(nestedDir); });
       break;
 
     // Cases where only 'teams' host-evaluated clauses might be present.
@@ -586,6 +587,7 @@ static void processHostEvalClauses(lower::AbstractConverter &converter,
       [[fallthrough]];
     case OMPD_target_teams_distribute:
     case OMPD_target_teams_distribute_simd:
+      cp.processCollapse(loc, eval, hostInfo.ops, hostInfo.iv);
       cp.processNumTeams(stmtCtx, hostInfo.ops);
       break;
 
diff --git a/flang/test/Lower/OpenMP/host-eval.f90 b/flang/test/Lower/OpenMP/host-eval.f90
index 32c52462b86a7..65258c91e5daf 100644
--- a/flang/test/Lower/OpenMP/host-eval.f90
+++ b/flang/test/Lower/OpenMP/host-eval.f90
@@ -155,3 +155,106 @@ subroutine distribute_parallel_do_simd()
   !$omp end distribute parallel do simd
   !$omp end teams
 end subroutine distribute_parallel_do_simd
+
+! BOTH-LABEL: func.func @_QPdistribute
+subroutine distribute()
+  ! BOTH: omp.target
+  
+  ! HOST-SAME: host_eval(%{{.*}} -> %[[LB:.*]], %{{.*}} -> %[[UB:.*]], %{{.*}} -> %[[STEP:.*]] : i32, i32, i32)
+  
+  ! DEVICE-NOT: host_eval({{.*}})
+  ! DEVICE-SAME: {
+
+  ! BOTH: omp.teams
+  !$omp target teams
+
+  ! BOTH: omp.distribute
+  ! BOTH-NEXT: omp.loop_nest
+
+  ! HOST-SAME: (%{{.*}}) : i32 = (%[[LB]]) to (%[[UB]]) inclusive step (%[[STEP]])
+  !$omp distribute
+  do i=1,10
+    call foo()
+  end do
+  !$omp end distribute
+  !$omp end target teams
+
+  ! BOTH: omp.target
+  ! BOTH-NOT: host_eval({{.*}})
+  ! BOTH-SAME: {
+  ! BOTH: omp.teams
+  !$omp target teams
+  call foo() !< Prevents this from being Generic-SPMD.
+
+  ! BOTH: omp.distribute
+  !$omp distribute
+  do i=1,10
+    call foo()
+  end do
+  !$omp end distribute
+  !$omp end target teams
+
+  ! BOTH: omp.teams
+  !$omp teams
+
+  ! BOTH: omp.distribute
+  !$omp distribute
+  do i=1,10
+    call foo()
+  end do
+  !$omp end distribute
+  !$omp end teams
+end subroutine distribute
+
+! BOTH-LABEL: func.func @_QPdistribute_simd
+subroutine distribute_simd()
+  ! BOTH: omp.target
+  
+  ! HOST-SAME: host_eval(%{{.*}} -> %[[LB:.*]], %{{.*}} -> %[[UB:.*]], %{{.*}} -> %[[STEP:.*]] : i32, i32, i32)
+  
+  ! DEVICE-NOT: host_eval({{.*}})
+  ! DEVICE-SAME: {
+
+  ! BOTH: omp.teams
+  !$omp target teams
+
+  ! BOTH: omp.distribute
+  ! BOTH-NEXT: omp.simd
+  ! BOTH-NEXT: omp.loop_nest
+
+  ! HOST-SAME: (%{{.*}}) : i32 = (%[[LB]]) to (%[[UB]]) inclusive step (%[[STEP]])
+  !$omp distribute simd
+  do i=1,10
+    call foo()
+  end do
+  !$omp end distribute simd
+  !$omp end target teams
+
+  ! BOTH: omp.target
+  ! BOTH-NOT: host_eval({{.*}})
+  ! BOTH-SAME: {
+  ! BOTH: omp.teams
+  !$omp target teams
+  call foo() !< Prevents this from being Generic-SPMD.
+
+  ! BOTH: omp.distribute
+  ! BOTH-NEXT: omp.simd
+  !$omp distribute simd
+  do i=1,10
+    call foo()
+  end do
+  !$omp end distribute simd
+  !$omp end target teams
+
+  ! BOTH: omp.teams
+  !$omp teams
+
+  ! BOTH: omp.distribute
+  ! BOTH-NEXT: omp.simd
+  !$omp distribute simd
+  do i=1,10
+    call foo()
+  end do
+  !$omp end distribute simd
+  !$omp end teams
+end subroutine distribute_simd