From 48bc21f08d87fd27bed13818ef73c44cd501e6c7 Mon Sep 17 00:00:00 2001
From: Matthew Stanley <1379tech@gmail.com>
Date: Sun, 23 Aug 2026 13:20:50 -0700
Subject: [PATCH] recompiler: tail-transfer image-edge fallthroughs

---
 recompiler/src/code_generator.cpp | 35 +++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/recompiler/src/code_generator.cpp b/recompiler/src/code_generator.cpp
index c7bd9b48..68a0c5fe 100644
--- a/recompiler/src/code_generator.cpp
+++ b/recompiler/src/code_generator.cpp
@@ -2788,6 +2788,24 @@ GeneratedFunction CodeGenerator::generate_function(
                                        fallthrough_name);
             }
         }
+    } else if (!cfg.block_order.empty()) {
+        // No in-image fallthrough function exists (region/image boundary): a
+        // reachable final block that runs off the end must publish its
+        // continuation PC. Falling off the C body would return with the
+        // entry-switch's consumed cpu->pc == 0, which the top-level trampoline
+        // reads as "program ended".
+        const BasicBlock& last_block = cfg.blocks.at(cfg.block_order.back());
+        bool runs_off_end =
+            last_block.exit_instr.type == ControlFlowType::None ||
+            ((last_block.exit_instr.type == ControlFlowType::Branch ||
+              last_block.exit_instr.type == ControlFlowType::Jump) &&
+             last_block.successors.empty());
+        bool is_reachable = last_block.is_entry || !last_block.predecessors.empty();
+        if (runs_off_end && is_reachable) {
+            body_ss << fmt::format(
+                "    cpu->pc = 0x{:08X}u; return;  /* image-edge fallthrough: tail-transfer */\n",
+                last_block.end_addr + 4u);
+        }
     }
     body_ss << "    ;  /* label compatibility: C requires a statement after the last label */\n";
     body_ss << "}\n";
@@ -3017,6 +3035,23 @@ std::vector<GeneratedFunction> CodeGenerator::generate_alias_group(
             body << fmt::format("    {}(cpu);  /* fallthrough to next function */\n",
                                 fallthrough_name);
         }
+    } else if (!cfg.block_order.empty() &&
+               live_blocks.count(cfg.block_order.back())) {
+        // Image-edge fallthrough (mirrors generate_function): no in-image next
+        // function exists, so a live final block that runs off the end must
+        // tail-transfer to its continuation PC instead of falling off the C
+        // body with cpu->pc still consumed to 0.
+        const BasicBlock& last_block = cfg.blocks.at(cfg.block_order.back());
+        bool runs_off_end =
+            (last_block.exit_instr.type == ControlFlowType::None) ||
+            ((last_block.exit_instr.type == ControlFlowType::Branch ||
+              last_block.exit_instr.type == ControlFlowType::Jump) &&
+             last_block.successors.empty());
+        if (runs_off_end) {
+            body << fmt::format(
+                "    cpu->pc = 0x{:08X}u; return;  /* image-edge fallthrough: tail-transfer */\n",
+                last_block.end_addr + 4u);
+        }
     }
     body << "    ;  /* label compatibility */\n";
     body << "}\n";