[Flang][Alias analysis] Fix alias analysis for omp private

Flang alias analysis crashes for omp private allocatable
item. The issue is described here: #116954
The corrsponding MLIR code for omp private allocatable object contains
omp.yield without any results. We should not implicitly assume
that all omp.yield operations for omp.private contain results.

Author: DominikAdamski

flang/lib/Optimizer/Analysis/AliasAnalysis.cpp

@@ -517,6 +517,8 @@ static Value getPrivateArg(omp::BlockArgOpenMPOpInterface &argIface,
           SymbolTable::lookupNearestSymbolFrom<omp::PrivateClauseOp>(
               op, cast<SymbolRefAttr>(opSym));
       privateOp.walk([&](omp::YieldOp yieldOp) {
+        if (!yieldOp.getResults().size())
+          return;
         // TODO Extend alias analysis if omp.yield points to
         // block argument value
         if (!yieldOp.getResults()[0].getDefiningOp())

flang/test/Analysis/AliasAnalysis/alias-analysis-omp-private-allocatable.mlir

@@ -0,0 +1,50 @@
+// Use --mlir-disable-threading so that the AA queries are serialized
+// as well as its diagnostic output.
+// RUN: fir-opt %s -pass-pipeline='builtin.module(func.func(test-fir-alias-analysis))' -split-input-file --mlir-disable-threading 2>&1 | FileCheck %s
+
+// Fortran code before simplification:
+// SUBROUTINE mysub(ns,ne)
+//      INTEGER  :: n
+//      REAL(KIND=8), DIMENSION(:), allocatable     :: ar1
+//      real(kind=8), dimension(20) :: ar2
+//      REAL(KIND=8), DIMENSION(20) :: d
+//
+//!$OMP parallel PRIVATE(ar1)
+//         d(1:1) = (/(DOT_PRODUCT(ar1(1:n), ar2(1:n)),n=1, 1)/)
+//!$OMP END parallel
+//   END SUBROUTINE
+
+// CHECK-LABEL: Testing : "testPrivateAllocatable"
+// CHECK: ar2#0 <-> ar1#0: NoAlias
+// CHECK: ar2#1 <-> ar1#0: NoAlias
+// CHECK: ar2#0 <-> ar1#1: NoAlias
+// CHECK: ar2#1 <-> ar1#1: NoAlias
+
+omp.private {type = private} @_QFmysubEar1_private_ref_box_heap_Uxf64 : !fir.ref<!fir.box<!fir.heap<!fir.array<?xf64>>>> alloc {
+^bb0(%arg0: !fir.ref<!fir.box<!fir.heap<!fir.array<?xf64>>>>):
+  %0 = fir.alloca !fir.box<!fir.heap<!fir.array<?xf64>>> {bindc_name = "ar1", pinned, uniq_name = "_QFmysubEar1"}
+  %5:2 = hlfir.declare %0 {fortran_attrs = #fir.var_attrs<allocatable>, uniq_name = "_QFmysubEar1"} : (!fir.ref<!fir.box<!fir.heap<!fir.array<?xf64>>>>) -> (!fir.ref<!fir.box<!fir.heap<!fir.array<?xf64>>>>, !fir.ref<!fir.box<!fir.heap<!fir.array<?xf64>>>>)
+  omp.yield(%5#0 : !fir.ref<!fir.box<!fir.heap<!fir.array<?xf64>>>>)
+} dealloc {
+^bb0(%arg0: !fir.ref<!fir.box<!fir.heap<!fir.array<?xf64>>>>):
+  omp.yield
+}
+func.func @testPrivateAllocatable(%arg0: !fir.ref<i32> {fir.bindc_name = "ns"}, %arg1: !fir.ref<i32> {fir.bindc_name = "ne"}) {
+  %0 = fir.dummy_scope : !fir.dscope
+  %1 = fir.alloca !fir.box<!fir.heap<!fir.array<?xf64>>> {bindc_name = "ar1", uniq_name = "_QFmysubEar1"}
+  %2 = fir.zero_bits !fir.heap<!fir.array<?xf64>>
+  %c0 = arith.constant 0 : index
+  %3 = fir.shape %c0 : (index) -> !fir.shape<1>
+  %4 = fir.embox %2(%3) : (!fir.heap<!fir.array<?xf64>>, !fir.shape<1>) -> !fir.box<!fir.heap<!fir.array<?xf64>>>
+  fir.store %4 to %1 : !fir.ref<!fir.box<!fir.heap<!fir.array<?xf64>>>>
+  %5:2 = hlfir.declare %1 {fortran_attrs = #fir.var_attrs<allocatable>, uniq_name = "_QFmysubEar1"} : (!fir.ref<!fir.box<!fir.heap<!fir.array<?xf64>>>>) -> (!fir.ref<!fir.box<!fir.heap<!fir.array<?xf64>>>>, !fir.ref<!fir.box<!fir.heap<!fir.array<?xf64>>>>)
+  %c20 = arith.constant 20 : index
+  %6 = fir.alloca !fir.array<20xf64> {bindc_name = "ar2", uniq_name = "_QFmysubEar2"}
+  %7 = fir.shape %c20 : (index) -> !fir.shape<1>
+  %8:2 = hlfir.declare %6(%7) {uniq_name = "_QFmysubEar2", test.ptr="ar2" } : (!fir.ref<!fir.array<20xf64>>, !fir.shape<1>) -> (!fir.ref<!fir.array<20xf64>>, !fir.ref<!fir.array<20xf64>>)
+  omp.parallel private(@_QFmysubEar1_private_ref_box_heap_Uxf64 %5#0 -> %arg2 : !fir.ref<!fir.box<!fir.heap<!fir.array<?xf64>>>>) {
+    %20:2 = hlfir.declare %arg2 {fortran_attrs = #fir.var_attrs<allocatable>, uniq_name = "_QFmysubEar1", test.ptr = "ar1"} : (!fir.ref<!fir.box<!fir.heap<!fir.array<?xf64>>>>) -> (!fir.ref<!fir.box<!fir.heap<!fir.array<?xf64>>>>, !fir.ref<!fir.box<!fir.heap<!fir.array<?xf64>>>>)
+    omp.terminator
+  }
+  return
+}