From 7865fbfe6d04a79a253a38eaec5c21c2bde110b5 Mon Sep 17 00:00:00 2001
From: samu698 <gpg@cerea.dev>
Date: Sat, 26 Oct 2024 15:18:47 +0200
Subject: [PATCH] LibJS: Don't generate useless jumps for if statement

If statements without an else clause generated jumps to the next
instruction, this commit fixes the if statement generation so that it
dosen't produce them anymore.

This is an example of JS code that generates the useless jumps
(a => if(a){}) ();
---
 .../Libraries/LibJS/Bytecode/ASTCodegen.cpp   | 23 ++++++++-----------
 1 file changed, 9 insertions(+), 14 deletions(-)

diff --git a/Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp b/Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp
index 242a225d3fd..5ed17e1e1dc 100644
--- a/Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp
+++ b/Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp
@@ -2330,7 +2330,8 @@ Bytecode::CodeGenerationErrorOr<Optional<ScopedOperand>> IfStatement::generate_b
 
     auto& true_block = generator.make_block();
     auto& false_block = generator.make_block();
-    auto& end_block = generator.make_block();
+    // NOTE: if there is no 'else' block the end block is the same as the false block
+    auto& end_block = m_alternate ? generator.make_block() : false_block;
 
     Optional<ScopedOperand> completion;
     if (generator.must_propagate_completion()) {
@@ -2347,25 +2348,19 @@ Bytecode::CodeGenerationErrorOr<Optional<ScopedOperand>> IfStatement::generate_b
     generator.switch_to_basic_block(true_block);
     auto consequent = TRY(m_consequent->generate_bytecode(generator, completion));
     if (!generator.is_current_block_terminated()) {
-        if (generator.must_propagate_completion()) {
-            if (consequent.has_value())
-                generator.emit<Bytecode::Op::Mov>(*completion, *consequent);
-        }
+        if (generator.must_propagate_completion() && consequent.has_value())
+            generator.emit<Bytecode::Op::Mov>(*completion, *consequent);
         generator.emit<Bytecode::Op::Jump>(Bytecode::Label { end_block });
     }
 
-    generator.switch_to_basic_block(false_block);
-
-    Optional<ScopedOperand> alternate;
     if (m_alternate) {
-        alternate = TRY(m_alternate->generate_bytecode(generator, completion));
-    }
-    if (!generator.is_current_block_terminated()) {
-        if (generator.must_propagate_completion()) {
-            if (alternate.has_value())
+        generator.switch_to_basic_block(false_block);
+        auto alternate = TRY(m_alternate->generate_bytecode(generator, completion));
+        if (!generator.is_current_block_terminated()) {
+            if (generator.must_propagate_completion() && alternate.has_value())
                 generator.emit<Bytecode::Op::Mov>(*completion, *alternate);
+            generator.emit<Bytecode::Op::Jump>(Bytecode::Label { end_block });
         }
-        generator.emit<Bytecode::Op::Jump>(Bytecode::Label { end_block });
     }
 
     generator.switch_to_basic_block(end_block);