Return vector for output alias

CHANGELOG.md

@@ -3,6 +3,12 @@
 Full documentation for MIGraphX is available at
 [https://rocmdocs.amd.com/projects/AMDMIGraphX/en/latest/](https://rocmdocs.amd.com/projects/AMDMIGraphX/en/latest/).
 
+## Develop Branch
+
+### Changed
+
+* Refactored instruction output alias to return a vector of aliases (#4540).
+
 ## MIGraphX 2.15 for ROCm 7.2.0
 
 ### Added

src/adjust_allocation.cpp

@@ -1,7 +1,7 @@
 /*
  * The MIT License (MIT)
  *
- * Copyright (c) 2015-2022 Advanced Micro Devices, Inc. All rights reserved.
+ * Copyright (c) 2015-2026 Advanced Micro Devices, Inc. All rights reserved.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -43,7 +43,10 @@ void adjust_allocation::apply(module& m) const
         if(ins->get_operator().is_context_free())
             continue;
 
-        auto alias_ins = instruction::get_output_alias(ins, true);
+        auto aliases = instruction::get_output_alias(ins, true);
+        if(aliases.size() != 1)
+            continue;
+        auto alias_ins = aliases.front();
         if(alias_ins->name() != model.name() and alias_ins->name() != "@param")
             continue;
         // shape allocated is different from actual shape

src/api/api.cpp

@@ -1,7 +1,7 @@
 /*
  * The MIT License (MIT)
  *
- * Copyright (c) 2015-2025 Advanced Micro Devices, Inc. All rights reserved.
+ * Copyright (c) 2015-2026 Advanced Micro Devices, Inc. All rights reserved.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -377,19 +377,9 @@ struct custom_operation
         return op.compute(std::move(ctx), std::move(output_shape), std::move(inputs));
     }
 
-    std::ptrdiff_t output_alias(std::vector<shape> inputs) const
+    std::vector<std::size_t> output_alias(std::vector<shape> inputs) const
     {
-        auto alias_vec = op.output_alias(std::move(inputs));
-        // TODO: For now, only support one output alias
-        if(alias_vec.empty())
-        {
-            return -1;
-        }
-        if(alias_vec.size() > 1)
-        {
-            MIGRAPHX_THROW("Currently, CustomOps in MIGraphX only supports one output_alias");
-        }
-        return alias_vec.front();
+        return op.output_alias(std::move(inputs));
     }
 
     bool runs_on_offload_target() const { return op.runs_on_offload_target(); }

src/driver/perf.cpp

@@ -1,7 +1,7 @@
 /*
  * The MIT License (MIT)
  *
- * Copyright (c) 2015-2025 Advanced Micro Devices, Inc. All rights reserved.
+ * Copyright (c) 2015-2026 Advanced Micro Devices, Inc. All rights reserved.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -118,19 +118,23 @@ bool is_offload_copy_set(const program& p)
     {
         if(i.name() == "hip::copy_to_gpu")
         {
-            auto copy_arg = instruction::get_output_alias(i.inputs().front(), true);
-            param_ins.erase(copy_arg);
+            auto copy_args = instruction::get_output_alias(i.inputs().front(), true);
+            for(auto copy_arg : copy_args)
+                param_ins.erase(copy_arg);
         }
         else if(i.name() == "@return")
         {
             auto return_args = i.inputs();
-            for(const auto& j : return_args)
-            {
-                auto alias_ins = instruction::get_output_alias(j, true);
-                if((alias_ins->name() == "@param" and param_ins.erase(alias_ins) == 0) or
-                   (alias_ins->name() != "hip::copy_from_gpu"))
+            return std::all_of(return_args.begin(), return_args.end(), [&](const auto& j) {
+                auto aliases = instruction::get_output_alias(j, true);
+                return std::all_of(aliases.begin(), aliases.end(), [&](instruction_ref alias_ins) {
+                    if(alias_ins->name() == "hip::copy_from_gpu")
+                        return true;
+                    if(alias_ins->name() == "@param")
+                        return not contains(param_ins, alias_ins);
                     return false;
-            }
+                });
+            });
         }
     }
     return param_ins.empty();

src/driver/trim.cpp

@@ -1,7 +1,7 @@
 /*
  * The MIT License (MIT)
  *
- * Copyright (c) 2015-2025 Advanced Micro Devices, Inc. All rights reserved.
+ * Copyright (c) 2015-2026 Advanced Micro Devices, Inc. All rights reserved.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -37,11 +37,11 @@ inline namespace MIGRAPHX_INLINE_NS {
 
 static instruction_ref capture_arg(std::unordered_set<instruction_ref>& s, instruction_ref ins)
 {
-    auto alias = instruction::get_output_alias(ins, true);
-    if(alias != ins)
+    auto aliases = instruction::get_output_alias(ins, true);
+    if(aliases.size() == 1 and aliases.front() != ins)
     {
         s.insert(ins);
-        return capture_arg(s, alias);
+        return capture_arg(s, aliases.front());
     }
     if(contains({"reshape", "contiguous"}, ins->name()))
     {

src/eliminate_concat.cpp

@@ -1,7 +1,7 @@
 /*
  * The MIT License (MIT)
  *
- * Copyright (c) 2015-2024 Advanced Micro Devices, Inc. All rights reserved.
+ * Copyright (c) 2015-2026 Advanced Micro Devices, Inc. All rights reserved.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -70,11 +70,14 @@ void eliminate_concat::apply(module& m) const
             // Where are the allocations for the tensors to be concatenated?
             std::vector<instruction_ref> allocations;
 
-            std::transform(
-                ins->inputs().begin(),
-                std::prev(ins->inputs().end()),
-                std::back_inserter(allocations),
-                [&](instruction_ref x) { return instruction::get_output_alias(x, true); });
+            std::transform(ins->inputs().begin(),
+                           std::prev(ins->inputs().end()),
+                           std::back_inserter(allocations),
+                           [&](instruction_ref x) {
+                               auto aliases = instruction::get_output_alias(x, true);
+                               // cppcheck-suppress returnDanglingLifetime
+                               return aliases.front();
+                           });
 
             if(std::any_of(allocations.begin(), allocations.end(), [&](auto x) {
                    return x->name() != concat_opt.allocate();

src/graphviz.cpp

@@ -1,7 +1,7 @@
 /*
  * The MIT License (MIT)
  *
- * Copyright (c) 2015-2025 Advanced Micro Devices, Inc. All rights reserved.
+ * Copyright (c) 2015-2026 Advanced Micro Devices, Inc. All rights reserved.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -114,7 +114,7 @@ std::string get_graph_color(const instruction_ref& ins)
     const auto& attr = op.attributes();
 
     bool context_free = is_context_free(op);
-    bool alias        = op.output_alias(to_shapes(ins->inputs())) >= 0;
+    bool alias        = not op.output_alias(to_shapes(ins->inputs())).empty();
 
     if(ins->can_eval())
     {

src/include/migraphx/instruction.hpp

@@ -1,7 +1,7 @@
 /*
  * The MIT License (MIT)
  *
- * Copyright (c) 2015-2025 Advanced Micro Devices, Inc. All rights reserved.
+ * Copyright (c) 2015-2026 Advanced Micro Devices, Inc. All rights reserved.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -140,7 +140,7 @@ struct MIGRAPHX_EXPORT instruction
 
     void finalize(context& ctx);
 
-    static instruction_ref get_output_alias(instruction_ref ins, bool shallow = false);
+    static std::vector<instruction_ref> get_output_alias(instruction_ref ins, bool shallow = false);
 
     void set_normalized(bool value = true);
     bool is_normalized() const;

src/include/migraphx/liveness.hpp

@@ -1,7 +1,7 @@
 /*
  * The MIT License (MIT)
  *
- * Copyright (c) 2015-2024 Advanced Micro Devices, Inc. All rights reserved.
+ * Copyright (c) 2015-2026 Advanced Micro Devices, Inc. All rights reserved.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -53,11 +53,12 @@ void liveness(const module& m, F f)
         auto add_live_variables = [&](const auto& inputs) {
             for(auto input : inputs)
             {
-                auto i = instruction::get_output_alias(input);
+                auto aliases = instruction::get_output_alias(input);
                 // Skip if variable comes from parent
-                if(not m.has_instruction(i))
-                    continue;
-                live_set.insert(i);
+                std::copy_if(aliases.begin(),
+                             aliases.end(),
+                             std::inserter(live_set, live_set.end()),
+                             [&](auto i) { return m.has_instruction(i); });
             }
         };
         add_live_variables(ins->inputs());

src/include/migraphx/op/as_shape.hpp

@@ -1,7 +1,7 @@
 /*
  * The MIT License (MIT)
  *
- * Copyright (c) 2015-2022 Advanced Micro Devices, Inc. All rights reserved.
+ * Copyright (c) 2015-2026 Advanced Micro Devices, Inc. All rights reserved.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -53,7 +53,7 @@ struct as_shape
     {
         return args.front().reshape(output_shape);
     }
-    std::ptrdiff_t output_alias(const std::vector<shape>&) const { return 0; }
+    std::vector<std::size_t> output_alias(const std::vector<shape>&) const { return {0}; }
 };
 
 } // namespace op

src/include/migraphx/op/broadcast.hpp

@@ -1,7 +1,7 @@
 /*
  * The MIT License (MIT)
  *
- * Copyright (c) 2015-2025 Advanced Micro Devices, Inc. All rights reserved.
+ * Copyright (c) 2015-2026 Advanced Micro Devices, Inc. All rights reserved.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -148,7 +148,7 @@ struct broadcast
     {
         return args[0].reshape(dyn_out.computed_shape);
     }
-    std::ptrdiff_t output_alias(const std::vector<shape>&) const { return 0; }
+    std::vector<std::size_t> output_alias(const std::vector<shape>&) const { return {0}; }
 
     value attributes() const { return {{"fillcolor", "#9ACD32" /* yellowgreen */}}; }
 };

src/include/migraphx/op/broadcast_for_dot.hpp

@@ -1,7 +1,7 @@
 /*
  * The MIT License (MIT)
  *
- * Copyright (c) 2015-2025 Advanced Micro Devices, Inc. All rights reserved.
+ * Copyright (c) 2015-2026 Advanced Micro Devices, Inc. All rights reserved.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -83,7 +83,7 @@ struct broadcast_for_dot
         return args[0].reshape(dyn_out.computed_shape);
     }
 
-    std::ptrdiff_t output_alias(const std::vector<shape>&) const { return 0; }
+    std::vector<std::size_t> output_alias(const std::vector<shape>&) const { return {0}; }
 
     value attributes() const { return {{"fillcolor", "#9ACD32" /* yellowgreen */}}; }
 };

src/include/migraphx/op/capture.hpp

@@ -1,7 +1,7 @@
 /*
  * The MIT License (MIT)
  *
- * Copyright (c) 2015-2022 Advanced Micro Devices, Inc. All rights reserved.
+ * Copyright (c) 2015-2026 Advanced Micro Devices, Inc. All rights reserved.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -66,7 +66,7 @@ struct capture
         return args.front();
     }
 
-    std::ptrdiff_t output_alias(const std::vector<shape>&) const { return 0; }
+    std::vector<std::size_t> output_alias(const std::vector<shape>&) const { return {0}; }
 };
 
 } // namespace op

src/include/migraphx/op/fill.hpp

@@ -1,7 +1,7 @@
 /*
  * The MIT License (MIT)
  *
- * Copyright (c) 2015-2023 Advanced Micro Devices, Inc. All rights reserved.
+ * Copyright (c) 2015-2026 Advanced Micro Devices, Inc. All rights reserved.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -60,7 +60,7 @@ struct fill
         return args[1];
     }
 
-    std::ptrdiff_t output_alias(const std::vector<shape>&) const { return 1; }
+    std::vector<std::size_t> output_alias(const std::vector<shape>&) const { return {1}; }
 };
 
 } // namespace op

src/include/migraphx/op/get_tuple_elem.hpp

@@ -1,7 +1,7 @@
 /*
  * The MIT License (MIT)
  *
- * Copyright (c) 2015-2022 Advanced Micro Devices, Inc. All rights reserved.
+ * Copyright (c) 2015-2026 Advanced Micro Devices, Inc. All rights reserved.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -67,7 +67,7 @@ struct get_tuple_elem
         return vec_args.at(index);
     }
 
-    std::ptrdiff_t output_alias(const std::vector<shape>&) const { return 0; }
+    std::vector<std::size_t> output_alias(const std::vector<shape>&) const { return {0}; }
 };
 
 } // namespace op

src/include/migraphx/op/identity.hpp

@@ -1,7 +1,7 @@
 /*
  * The MIT License (MIT)
  *
- * Copyright (c) 2015-2024 Advanced Micro Devices, Inc. All rights reserved.
+ * Copyright (c) 2015-2026 Advanced Micro Devices, Inc. All rights reserved.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -39,7 +39,7 @@ struct identity
 
     value attributes() const { return {{"pointwise", true}, {"point_op", "${0}"}}; }
 
-    std::ptrdiff_t output_alias(const std::vector<shape>&) const { return 0; }
+    std::vector<std::size_t> output_alias(const std::vector<shape>&) const { return {0}; }
 };
 
 } // namespace op

src/include/migraphx/op/load.hpp

@@ -1,7 +1,7 @@
 /*
  * The MIT License (MIT)
  *
- * Copyright (c) 2015-2022 Advanced Micro Devices, Inc. All rights reserved.
+ * Copyright (c) 2015-2026 Advanced Micro Devices, Inc. All rights reserved.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -58,7 +58,7 @@ struct load
         return argument{s, args[0].data() + offset};
     }
     lifetime get_lifetime() const { return lifetime::borrow; }
-    std::ptrdiff_t output_alias(const std::vector<shape>&) const { return 0; }
+    std::vector<std::size_t> output_alias(const std::vector<shape>&) const { return {0}; }
 
     friend std::ostream& operator<<(std::ostream& os, const load& op)
     {

src/include/migraphx/op/multibroadcast.hpp

@@ -1,7 +1,7 @@
 /*
  * The MIT License (MIT)
  *
- * Copyright (c) 2015-2025 Advanced Micro Devices, Inc. All rights reserved.
+ * Copyright (c) 2015-2026 Advanced Micro Devices, Inc. All rights reserved.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -115,7 +115,7 @@ struct multibroadcast
     {
         return args[0].reshape(dyn_out.computed_shape);
     }
-    std::ptrdiff_t output_alias(const std::vector<shape>&) const { return 0; }
+    std::vector<std::size_t> output_alias(const std::vector<shape>&) const { return {0}; }
 };
 
 } // namespace op