[flang-commits] [flang] [flang] Support fir.pack_array in FIR alias analysis. (PR #131946)

[Slava Zakharin via flang-commits]

https://github.com/vzakhari updated https://github.com/llvm/llvm-project/pull/131946

>From e125dcda783f9be5141c05c78e5572938ccd7d21 Mon Sep 17 00:00:00 2001
From: Slava Zakharin <szakharin at nvidia.com>
Date: Tue, 18 Mar 2025 17:56:42 -0700
Subject: [PATCH 1/2] [flang] Support fir.pack_array in FIR alias analysis.

`fir.pack_array` is just a pass-through op for the process
of finding the source in FIR alias analysis (as defined in #127147).
---
 .../lib/Optimizer/Analysis/AliasAnalysis.cpp  |  7 +++++++
 .../alias-analysis-pack-array.fir             | 21 +++++++++++++++++++
 2 files changed, 28 insertions(+)
 create mode 100644 flang/test/Analysis/AliasAnalysis/alias-analysis-pack-array.fir

diff --git a/flang/lib/Optimizer/Analysis/AliasAnalysis.cpp b/flang/lib/Optimizer/Analysis/AliasAnalysis.cpp
index 2ff8ec05782c1..e953f4472379d 100644
--- a/flang/lib/Optimizer/Analysis/AliasAnalysis.cpp
+++ b/flang/lib/Optimizer/Analysis/AliasAnalysis.cpp
@@ -542,6 +542,13 @@ AliasAnalysis::Source AliasAnalysis::getSource(mlir::Value v,
           v = op->getOperand(0);
           defOp = v.getDefiningOp();
         })
+        .Case<fir::PackArrayOp>([&](auto op) {
+          // The packed array is not distinguishable from the original
+          // array, so skip PackArrayOp and track further through
+          // the array operand.
+          v = op.getArray();
+          defOp = v.getDefiningOp();
+        })
         .Case<fir::BoxAddrOp>([&](auto op) {
           v = op->getOperand(0);
           defOp = v.getDefiningOp();
diff --git a/flang/test/Analysis/AliasAnalysis/alias-analysis-pack-array.fir b/flang/test/Analysis/AliasAnalysis/alias-analysis-pack-array.fir
new file mode 100644
index 0000000000000..8de4605928912
--- /dev/null
+++ b/flang/test/Analysis/AliasAnalysis/alias-analysis-pack-array.fir
@@ -0,0 +1,21 @@
+// Test alias analysis queries for dummy arguments wired
+// through fir.pack_array.
+// fir.pack_array is a pass-through operation for FIR alias analysis.
+// RUN: fir-opt %s --test-fir-alias-analysis -split-input-file --mlir-disable-threading 2>&1 | FileCheck %s
+
+// CHECK: test1_y(1)#0 <-> test1_x(1)#0: NoAlias
+func.func @_QFtest1(%arg0: !fir.box<!fir.array<?xf32>> {fir.bindc_name = "x"}, %arg1: !fir.box<!fir.array<?xf32>> {fir.bindc_name = "y"}) {
+  %c1 = arith.constant 1 : index
+  %0 = fir.dummy_scope : !fir.dscope
+  %1 = fir.pack_array %arg0 heap whole : (!fir.box<!fir.array<?xf32>>) -> !fir.box<!fir.array<?xf32>>
+  %2:2 = hlfir.declare %1 dummy_scope %0 {uniq_name = "_QFtest1Ex"} : (!fir.box<!fir.array<?xf32>>, !fir.dscope) -> (!fir.box<!fir.array<?xf32>>, !fir.box<!fir.array<?xf32>>)
+  %3 = fir.pack_array %arg1 heap whole : (!fir.box<!fir.array<?xf32>>) -> !fir.box<!fir.array<?xf32>>
+  %4:2 = hlfir.declare %3 dummy_scope %0 {uniq_name = "_QFtest1Ey"} : (!fir.box<!fir.array<?xf32>>, !fir.dscope) -> (!fir.box<!fir.array<?xf32>>, !fir.box<!fir.array<?xf32>>)
+  %5 = hlfir.designate %4#0 (%c1) {test.ptr = "test1_y(1)"} : (!fir.box<!fir.array<?xf32>>, index) -> !fir.ref<f32>
+  %6 = fir.load %5 : !fir.ref<f32>
+  %7 = hlfir.designate %2#0 (%c1) {test.ptr = "test1_x(1)"} : (!fir.box<!fir.array<?xf32>>, index) -> !fir.ref<f32>
+  hlfir.assign %6 to %7 : f32, !fir.ref<f32>
+  fir.unpack_array %3 to %arg1 heap : !fir.box<!fir.array<?xf32>>
+  fir.unpack_array %1 to %arg0 heap : !fir.box<!fir.array<?xf32>>
+  return
+}

>From 66ee2a2db71f60fdb42896c99e086914c683e424 Mon Sep 17 00:00:00 2001
From: Slava Zakharin <szakharin at nvidia.com>
Date: Wed, 19 Mar 2025 16:57:55 -0700
Subject: [PATCH 2/2] Setting `approximateSource` to true for `fir.pack_array`.

---
 .../lib/Optimizer/Analysis/AliasAnalysis.cpp  |  1 +
 .../alias-analysis-pack-array.fir             | 28 +++++++++++++++++--
 2 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/flang/lib/Optimizer/Analysis/AliasAnalysis.cpp b/flang/lib/Optimizer/Analysis/AliasAnalysis.cpp
index e953f4472379d..bda98871a1c7a 100644
--- a/flang/lib/Optimizer/Analysis/AliasAnalysis.cpp
+++ b/flang/lib/Optimizer/Analysis/AliasAnalysis.cpp
@@ -548,6 +548,7 @@ AliasAnalysis::Source AliasAnalysis::getSource(mlir::Value v,
           // the array operand.
           v = op.getArray();
           defOp = v.getDefiningOp();
+          approximateSource = true;
         })
         .Case<fir::BoxAddrOp>([&](auto op) {
           v = op->getOperand(0);
diff --git a/flang/test/Analysis/AliasAnalysis/alias-analysis-pack-array.fir b/flang/test/Analysis/AliasAnalysis/alias-analysis-pack-array.fir
index 8de4605928912..06d090407a26b 100644
--- a/flang/test/Analysis/AliasAnalysis/alias-analysis-pack-array.fir
+++ b/flang/test/Analysis/AliasAnalysis/alias-analysis-pack-array.fir
@@ -3,7 +3,25 @@
 // fir.pack_array is a pass-through operation for FIR alias analysis.
 // RUN: fir-opt %s --test-fir-alias-analysis -split-input-file --mlir-disable-threading 2>&1 | FileCheck %s
 
-// CHECK: test1_y(1)#0 <-> test1_x(1)#0: NoAlias
+// The two pointers referencing two different maybe repacked
+// versions of the original dummy arguments do not alias:
+// CHECK-DAG: test1_y_repack(1)#0 <-> test1_x_repack(1)#0: NoAlias
+// CHECK-DAG: test1_x_orig(1)#0 <-> test1_y_orig(1)#0: NoAlias
+
+// Repacked dummy does not alias with another original dummy:
+// CHECK-DAG: test1_y_repack(1)#0 <-> test1_x_orig(1)#0: NoAlias
+// CHECK-DAG: test1_x_repack(1)#0 <-> test1_y_orig(1)#0: NoAlias
+
+// Repacked dummy may alias with its original:
+// CHECK-DAG: test1_x_repack(1)#0 <-> test1_x_orig(1)#0: MayAlias
+// CHECK-DAG: test1_y_repack(1)#0 <-> test1_y_orig(1)#0: MayAlias
+
+// Ideally, these should report MustAlias, but MayAlias
+// may work as well:
+// CHECK-DAG: test1_y_repack(1)#0 <-> test1_y_repack2(1)#0: MayAlias
+// CHECK-DAG: test1_x_repack(1)#0 <-> test1_x_repack2(1)#0: MayAlias
+
+
 func.func @_QFtest1(%arg0: !fir.box<!fir.array<?xf32>> {fir.bindc_name = "x"}, %arg1: !fir.box<!fir.array<?xf32>> {fir.bindc_name = "y"}) {
   %c1 = arith.constant 1 : index
   %0 = fir.dummy_scope : !fir.dscope
@@ -11,11 +29,15 @@ func.func @_QFtest1(%arg0: !fir.box<!fir.array<?xf32>> {fir.bindc_name = "x"}, %
   %2:2 = hlfir.declare %1 dummy_scope %0 {uniq_name = "_QFtest1Ex"} : (!fir.box<!fir.array<?xf32>>, !fir.dscope) -> (!fir.box<!fir.array<?xf32>>, !fir.box<!fir.array<?xf32>>)
   %3 = fir.pack_array %arg1 heap whole : (!fir.box<!fir.array<?xf32>>) -> !fir.box<!fir.array<?xf32>>
   %4:2 = hlfir.declare %3 dummy_scope %0 {uniq_name = "_QFtest1Ey"} : (!fir.box<!fir.array<?xf32>>, !fir.dscope) -> (!fir.box<!fir.array<?xf32>>, !fir.box<!fir.array<?xf32>>)
-  %5 = hlfir.designate %4#0 (%c1) {test.ptr = "test1_y(1)"} : (!fir.box<!fir.array<?xf32>>, index) -> !fir.ref<f32>
+  %5 = fir.box_addr %4#0 {test.ptr = "test1_y_repack(1)"} : (!fir.box<!fir.array<?xf32>>) -> !fir.ref<f32>
+  %52 = fir.box_addr %4#0 {test.ptr = "test1_y_repack2(1)"} : (!fir.box<!fir.array<?xf32>>) -> !fir.ref<f32>
   %6 = fir.load %5 : !fir.ref<f32>
-  %7 = hlfir.designate %2#0 (%c1) {test.ptr = "test1_x(1)"} : (!fir.box<!fir.array<?xf32>>, index) -> !fir.ref<f32>
+  %7 = fir.box_addr %2#0 {test.ptr = "test1_x_repack(1)"} : (!fir.box<!fir.array<?xf32>>) -> !fir.ref<f32>
+  %72 = fir.box_addr %2#0 {test.ptr = "test1_x_repack2(1)"} : (!fir.box<!fir.array<?xf32>>) -> !fir.ref<f32>
   hlfir.assign %6 to %7 : f32, !fir.ref<f32>
   fir.unpack_array %3 to %arg1 heap : !fir.box<!fir.array<?xf32>>
   fir.unpack_array %1 to %arg0 heap : !fir.box<!fir.array<?xf32>>
+  %8 = fir.box_addr %arg0 {test.ptr = "test1_x_orig(1)"} : (!fir.box<!fir.array<?xf32>>) -> !fir.ref<f32>
+  %9 = fir.box_addr %arg1 {test.ptr = "test1_y_orig(1)"} : (!fir.box<!fir.array<?xf32>>) -> !fir.ref<f32>
   return
 }