[flang] Treat hlfir.associate as Allocate for FIR alias analysis.

Early HLFIR optimizations may experience problems with values
produced by hlfir.associate. In most cases this is a unique
local memory allocation, but it can also reuse some other
hlfir.expr memory sometimes. It seems to be safe to assume
unique allocation for trivial types, since we always
allocate new memory for them.

Author: vzakhari

flang/lib/Optimizer/Analysis/AliasAnalysis.cpp

@@ -540,6 +540,20 @@ AliasAnalysis::Source AliasAnalysis::getSource(mlir::Value v,
           v = op.getVar();
           defOp = v.getDefiningOp();
         })
+        .Case<hlfir::AssociateOp>([&](auto op) {
+          mlir::Value source = op.getSource();
+          if (fir::isa_trivial(source.getType())) {
+            // Trivial values will always use distinct temp memory,
+            // so we can classify this as Allocate and stop.
+            type = SourceKind::Allocate;
+            breakFromLoop = true;
+          } else {
+            // AssociateOp may reuse the expression storage,
+            // so we have to trace further.
+            v = source;
+            defOp = v.getDefiningOp();
+          }
+        })
         .Case<fir::AllocaOp, fir::AllocMemOp>([&](auto op) {
           // Unique memory allocation.
           type = SourceKind::Allocate;

flang/test/HLFIR/opt-bufferization-eval_in_mem-with-associate.fir

@@ -0,0 +1,30 @@
+// RUN: fir-opt --opt-bufferization %s | FileCheck %s
+
+// Verify that hlfir.eval_in_mem uses the LHS array instead
+// of allocating a temporary.
+func.func @_QPtest() {
+  %cst = arith.constant 1.000000e+00 : f32
+  %c10 = arith.constant 10 : index
+  %0 = fir.dummy_scope : !fir.dscope
+  %1 = fir.alloca !fir.array<10xf32> {bindc_name = "x", uniq_name = "_QFtestEx"}
+  %2 = fir.shape %c10 : (index) -> !fir.shape<1>
+  %3:2 = hlfir.declare %1(%2) {uniq_name = "_QFtestEx"} : (!fir.ref<!fir.array<10xf32>>, !fir.shape<1>) -> (!fir.ref<!fir.array<10xf32>>, !fir.ref<!fir.array<10xf32>>)
+  %4:3 = hlfir.associate %cst {adapt.valuebyref} : (f32) -> (!fir.ref<f32>, !fir.ref<f32>, i1)
+  %5 = hlfir.eval_in_mem shape %2 : (!fir.shape<1>) -> !hlfir.expr<10xf32> {
+  ^bb0(%arg0: !fir.ref<!fir.array<10xf32>>):
+    %6 = fir.call @_QParray_func(%4#0) fastmath<contract> : (!fir.ref<f32>) -> !fir.array<10xf32>
+    fir.save_result %6 to %arg0(%2) : !fir.array<10xf32>, !fir.ref<!fir.array<10xf32>>, !fir.shape<1>
+  }
+  hlfir.assign %5 to %3#0 : !hlfir.expr<10xf32>, !fir.ref<!fir.array<10xf32>>
+  hlfir.end_associate %4#1, %4#2 : !fir.ref<f32>, i1
+  hlfir.destroy %5 : !hlfir.expr<10xf32>
+  return
+}
+// CHECK-LABEL:   func.func @_QPtest() {
+// CHECK:           %[[VAL_0:.*]] = arith.constant 1.000000e+00 : f32
+// CHECK:           %[[VAL_3:.*]] = fir.alloca !fir.array<10xf32> {bindc_name = "x", uniq_name = "_QFtestEx"}
+// CHECK:           %[[VAL_5:.*]]:2 = hlfir.declare %[[VAL_3]](%[[VAL_4:.*]]) {uniq_name = "_QFtestEx"} : (!fir.ref<!fir.array<10xf32>>, !fir.shape<1>) -> (!fir.ref<!fir.array<10xf32>>, !fir.ref<!fir.array<10xf32>>)
+// CHECK:           %[[VAL_6:.*]]:3 = hlfir.associate %[[VAL_0]] {adapt.valuebyref} : (f32) -> (!fir.ref<f32>, !fir.ref<f32>, i1)
+// CHECK:           %[[VAL_7:.*]] = fir.call @_QParray_func(%[[VAL_6]]#0) fastmath<contract> : (!fir.ref<f32>) -> !fir.array<10xf32>
+// CHECK:           fir.save_result %[[VAL_7]] to %[[VAL_5]]#0(%[[VAL_4]]) : !fir.array<10xf32>, !fir.ref<!fir.array<10xf32>>, !fir.shape<1>
+// CHECK:           hlfir.end_associate %[[VAL_6]]#1, %[[VAL_6]]#2 : !fir.ref<f32>, i1