From bb9230bbcd7b4f8152a4b2188285b4c1fdf3969f Mon Sep 17 00:00:00 2001
From: Todderod <christoffer.todderod@gmail.com>
Date: Wed, 8 Nov 2023 20:21:48 +0100
Subject: [PATCH] LibJS: Remove redundant Store op

If the property for GetByValue in Generator::load_from_reference
is a calculated value this would be stored in an allocated
register and returned from the function. Not all callers want
this information however, so now only give it out when asked for.

Reduced the instruction count for Kraken/ai-astar.js function
"neighbours" from 214 to 192.
---
 .../Libraries/LibJS/Bytecode/ASTCodegen.cpp   |  6 +++---
 .../Libraries/LibJS/Bytecode/Generator.cpp    | 21 ++++++++++++-------
 Userland/Libraries/LibJS/Bytecode/Generator.h |  6 +++++-
 3 files changed, 21 insertions(+), 12 deletions(-)

diff --git a/Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp b/Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp
index d4d97e52a4c..2e73b7303d8 100644
--- a/Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp
+++ b/Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp
@@ -525,7 +525,7 @@ Bytecode::CodeGenerationErrorOr<void> AssignmentExpression::generate_bytecode(By
     VERIFY(m_lhs.has<NonnullRefPtr<Expression const>>());
     auto& lhs = m_lhs.get<NonnullRefPtr<Expression const>>();
 
-    auto reference_registers = TRY(generator.emit_load_from_reference(lhs));
+    auto reference_registers = TRY(generator.emit_load_from_reference(lhs, Bytecode::Generator::CollectRegisters::Yes));
 
     Bytecode::BasicBlock* rhs_block_ptr { nullptr };
     Bytecode::BasicBlock* end_block_ptr { nullptr };
@@ -1057,7 +1057,7 @@ Bytecode::CodeGenerationErrorOr<void> ArrayExpression::generate_bytecode(Bytecod
 Bytecode::CodeGenerationErrorOr<void> MemberExpression::generate_bytecode(Bytecode::Generator& generator) const
 {
     Bytecode::Generator::SourceLocationScope scope(generator, *this);
-    (void)TRY(generator.emit_load_from_reference(*this));
+    (void)TRY(generator.emit_load_from_reference(*this, Bytecode::Generator::CollectRegisters::No));
     return {};
 }
 
@@ -2258,7 +2258,7 @@ Bytecode::CodeGenerationErrorOr<void> TaggedTemplateLiteral::generate_bytecode(B
 Bytecode::CodeGenerationErrorOr<void> UpdateExpression::generate_bytecode(Bytecode::Generator& generator) const
 {
     Bytecode::Generator::SourceLocationScope scope(generator, *this);
-    auto reference_registers = TRY(generator.emit_load_from_reference(*m_argument));
+    auto reference_registers = TRY(generator.emit_load_from_reference(*m_argument, Bytecode::Generator::CollectRegisters::Yes));
 
     Optional<Bytecode::Register> previous_value_for_postfix_reg;
     if (!m_prefixed) {
diff --git a/Userland/Libraries/LibJS/Bytecode/Generator.cpp b/Userland/Libraries/LibJS/Bytecode/Generator.cpp
index 56735e7f15f..678904f690b 100644
--- a/Userland/Libraries/LibJS/Bytecode/Generator.cpp
+++ b/Userland/Libraries/LibJS/Bytecode/Generator.cpp
@@ -205,7 +205,7 @@ CodeGenerationErrorOr<Generator::ReferenceRegisters> Generator::emit_super_refer
     };
 }
 
-CodeGenerationErrorOr<Optional<Generator::ReferenceRegisters>> Generator::emit_load_from_reference(JS::ASTNode const& node)
+CodeGenerationErrorOr<Optional<Generator::ReferenceRegisters>> Generator::emit_load_from_reference(JS::ASTNode const& node, CollectRegisters collect_registers)
 {
     if (is<Identifier>(node)) {
         auto& identifier = static_cast<Identifier const&>(node);
@@ -238,15 +238,20 @@ CodeGenerationErrorOr<Optional<Generator::ReferenceRegisters>> Generator::emit_l
                 emit<Bytecode::Op::Store>(object_reg);
 
                 TRY(expression.property().generate_bytecode(*this));
-                auto property_reg = allocate_register();
-                emit<Bytecode::Op::Store>(property_reg);
+                Optional<Register> property_reg {};
+                if (collect_registers == CollectRegisters::Yes) {
+                    property_reg = allocate_register();
+                    emit<Bytecode::Op::Store>(property_reg.value());
+                }
 
                 emit<Bytecode::Op::GetByValue>(object_reg);
-                return ReferenceRegisters {
-                    .base = object_reg,
-                    .referenced_name = property_reg,
-                    .this_value = object_reg,
-                };
+                if (collect_registers == CollectRegisters::Yes)
+                    return ReferenceRegisters {
+                        .base = object_reg,
+                        .referenced_name = property_reg.value(),
+                        .this_value = object_reg,
+                    };
+                return Optional<ReferenceRegisters> {};
             } else if (expression.property().is_identifier()) {
                 auto identifier_table_ref = intern_identifier(verify_cast<Identifier>(expression.property()).string());
                 emit_get_by_id(identifier_table_ref);
diff --git a/Userland/Libraries/LibJS/Bytecode/Generator.h b/Userland/Libraries/LibJS/Bytecode/Generator.h
index d549da998d0..4945259277a 100644
--- a/Userland/Libraries/LibJS/Bytecode/Generator.h
+++ b/Userland/Libraries/LibJS/Bytecode/Generator.h
@@ -98,7 +98,11 @@ public:
         Register this_value;                // [[ThisValue]]
     };
 
-    CodeGenerationErrorOr<Optional<ReferenceRegisters>> emit_load_from_reference(JS::ASTNode const&);
+    enum class CollectRegisters {
+        Yes,
+        No
+    };
+    CodeGenerationErrorOr<Optional<ReferenceRegisters>> emit_load_from_reference(JS::ASTNode const&, CollectRegisters);
     CodeGenerationErrorOr<void> emit_store_to_reference(JS::ASTNode const&);
     CodeGenerationErrorOr<void> emit_store_to_reference(ReferenceRegisters const&);
     CodeGenerationErrorOr<void> emit_delete_reference(JS::ASTNode const&);