Add immediate addressing mode for short branches and BRK to support some ugly tricks

docs/lang/assembly.md

@@ -13,6 +13,9 @@ There are two ways to include raw assembly code in your Millfork programs:
 Millfork inline assembly uses the same three-letter opcodes as most other 6502 assemblers.
 Indexing syntax is also the same. Only instructions available on the current CPU architecture are available.
 
+The short branching instructions and the `BRK` instruction support the immediate addressing mode,
+for more control over code generation.
+
 The `BBRn/BBSn/SMBn/RMBn` instructions cannot parameterize the tested bit. The syntax is as follows:
 
     BBR1 $10,label

src/main/scala/millfork/assembly/mos/opt/CoarseFlowAnalyzer.scala

@@ -136,6 +136,10 @@ object CoarseFlowAnalyzer {
           case AssemblyLine0(op, Implied, _) if FlowAnalyzerForImplied.hasDefinition(op) =>
             currentStatus = FlowAnalyzerForImplied.get(op)(currentStatus)
 
+          case AssemblyLine0(op, Immediate, _) if OpcodeClasses.ShortBranching(op) =>
+            // don't even both optimizing functions with weird jumps, it's futile
+            return cache.put(code, List.fill[CpuStatus](code.length)(initialStatus))
+
           case AssemblyLine0(op, Immediate | WordImmediate, NumericConstant(nn, _)) if FlowAnalyzerForImmediate.hasDefinition(op) =>
             currentStatus = FlowAnalyzerForImmediate.get(op)(nn.toInt, currentStatus)
 

src/main/scala/millfork/assembly/mos/opt/ReverseFlowAnalyzer.scala

@@ -172,6 +172,8 @@ object ReverseFlowAnalyzer {
               case _ => false
             }
             currentImportance = if (labelIndex < 0) finalImportance else importanceArray(labelIndex) ~ currentImportance
+          case AssemblyLine0(opcode, Immediate, _) if OpcodeClasses.ShortConditionalBranching(opcode) =>
+            currentImportance = finalImportance
           case AssemblyLine0(opcode, ZeroPageWithRelative, StructureConstant(_, List(_, MemoryAddressConstant(Label(l))))) if OpcodeClasses.SingleBitBranch(opcode) =>
             val L = l
             val labelIndex = codeArray.indexWhere {

src/main/scala/millfork/output/MosAssembler.scala

@@ -397,6 +397,7 @@ object MosAssembler {
   op(BEQ, Relative, 0xF0)
 
   op(BRK, Implied, 0)
+  op(BRK, Immediate, 0)
 
   op(CMP, Immediate, 0xC9)
   op(CMP, ZeroPage, 0xC5)