CPU/CodeCache: Don't choke on indirect branches in delay slot

Fixes emulator crash/memory usage explosion in Shadow Master.

src/core/cpu_code_cache.cpp

@@ -527,6 +527,11 @@ bool CompileBlock(CodeBlock* block)
         Log_WarningPrintf("Conditional branch delay slot at %08X, skipping block", cbi.pc);
         return false;
       }
+      if (!IsDirectBranchInstruction(cbi.instruction))
+      {
+        Log_WarningPrintf("Indirect branch in delay slot at %08X, skipping block", cbi.pc);
+        return false;
+      }
 
       // change the pc for the second branch's delay slot, it comes from the first branch
       const CodeBlockInstruction& prev_cbi = block->instructions.back();

src/core/cpu_types.cpp

@@ -80,6 +80,24 @@ bool IsUnconditionalBranchInstruction(const Instruction& instruction)
   }
 }
 
+bool IsDirectBranchInstruction(const Instruction& instruction)
+{
+  switch (instruction.op)
+  {
+    case InstructionOp::j:
+    case InstructionOp::jal:
+    case InstructionOp::b:
+    case InstructionOp::beq:
+    case InstructionOp::bgtz:
+    case InstructionOp::blez:
+    case InstructionOp::bne:
+      return true;
+
+    default:
+      return false;
+  }
+}
+
 u32 GetBranchInstructionTarget(const Instruction& instruction, u32 instruction_pc)
 {
   switch (instruction.op)
@@ -96,6 +114,7 @@ u32 GetBranchInstructionTarget(const Instruction& instruction, u32 instruction_p
       return instruction_pc + 4 + (instruction.i.imm_sext32() << 2);
 
     default:
+      Panic("Trying to get branch target of indirect or invalid branch");
       return instruction_pc;
   }
 }

src/core/cpu_types.h

@@ -213,6 +213,7 @@ union Instruction
 // Instruction helpers.
 bool IsBranchInstruction(const Instruction& instruction);
 bool IsUnconditionalBranchInstruction(const Instruction& instruction);
+bool IsDirectBranchInstruction(const Instruction& instruction);
 u32 GetBranchInstructionTarget(const Instruction& instruction, u32 instruction_pc);
 bool IsMemoryLoadInstruction(const Instruction& instruction);
 bool IsMemoryStoreInstruction(const Instruction& instruction);