fix: prevent internal errors when for-loop bodies always exit (#269)

---------

- build tuple iteration in an order such that special case of not checking reachability is no longer required
- simplify tuple, indexable, and urange looping code
- improve tuple iteration code gen
- test all combinations of supported iteration types

examples/sizes.txt

@@ -11,21 +11,21 @@
   arc4_types/Arc4BoolType                          412        76    336        76      0 
   arc4_types/Arc4DynamicBytes                      389       190    199       190      0 
   arc4_types/Arc4DynamicStringArray                285       112    173       112      0 
-  arc4_types/Arc4MutableParams                     511       303    208       295      8 
+  arc4_types/Arc4MutableParams                     501       295    206       292      3 
   arc4_types/Arc4Mutation                         3260      1464   1796      1464      0 
   arc4_types/Arc4NumericTypes                      752       201    551       201      0 
   arc4_types/Arc4RefTypes                           94        47     47        47      0 
   arc4_types/Arc4StringTypes                       469        35    434        35      0 
   arc4_types/Arc4StructsFromAnotherModule           73        12     61        12      0 
-  arc4_types/Arc4StructsType                       323       247     76       247      0 
+  arc4_types/Arc4StructsType                       318       239     79       239      0 
   arc4_types/Arc4TuplesType                        886       138    748       138      0 
   arc_28/EventEmitter                              167       121     46       121      0 
   asset/Reference                                  269       261      8       261      0 
   auction/Auction                                  573       522     51       522      0 
   augmented_assignment/Augmented                   159       156      3       156      0 
   avm_types_in_abi/Test                            412       336     76       336      0 
   biguint_binary_ops/BiguintBinaryOps              154         8    146         8      0 
-  boolean_binary_ops/BooleanBinaryOps              361       305     56       305      0 
+  boolean_binary_ops/BooleanBinaryOps              350       292     58       292      0 
   box_storage/Box                                 1813      1442    371      1442      0 
   bytes_ops/BiguintBinaryOps                       139       139      0       139      0 
   calculator                                       349       317     32       315      2 
@@ -40,7 +40,7 @@
   control_op_simplification                         48        44      4        38      6 
   dup2_optimization_bug                             26        22      4        22      0 
   edverify/Verify                                   43        37      6        37      0 
-  enumeration/Enumeration                          562       501     61       501      0 
+  enumeration/Enumeration                          547       483     64       483      0 
   everything                                       498       448     50       448      0 
   global_state/AppState                            479       464     15       464      0 
   hello_world/HelloWorld                            24        22      2        22      0 
@@ -57,6 +57,9 @@
   inner_transactions/itxn_loop                     192       184      8       184      0 
   intrinsics/ImmediateVariants                     166       162      4       162      0 
   intrinsics/Overloaded                             68        48     20        48      0 
+  iteration/IndexableIterationTest                 772       711     61       711      0 
+  iteration/TupleIterationTest                     521       453     68       453      0 
+  iteration/URangeIterationTest                   1097       598    499       598      0 
   koopman                                           16         9      7         9      0 
   less_simple                                      173       148     25       148      0 
   literals/LiteralFolding                          318       149    169       149      0 
@@ -71,7 +74,6 @@
   nested_loops/Nested                              239       201     38       201      0 
   regression_118                                   148       100     48       100      0 
   reinterpret_cast                                 127       109     18       109      0 
-  reversed_iteration                               833       547    286       547      0 
   scratch_slots                                     71        67      4        67      0 
   scratch_slots/2                                   71        67      4        67      0 
   scratch_slots/MyOther                              8         8      0         8      0 
@@ -91,12 +93,12 @@
   template_variables/TemplateVariables             168       155     13       155      0 
   tictactoe/TicTacToe                              835       682    153       670     12 
   too_many_permutations                            112       106      6       106      0 
-  transaction/Transaction                          996       932     64       932      0 
+  transaction/Transaction                          973       906     67       906      0 
   tuple_support/TupleComparisons                   136        75     61        75      0 
-  tuple_support/TupleSupport                       651       413    238       413      0 
+  tuple_support/TupleSupport                       643       404    239       404      0 
   typed_abi_call/Greeter                          2861      2446    415      2446      0 
   typed_abi_call/Logger                            896       762    134       762      0 
-  unary/Unary                                      136        96     40        96      0 
+  unary/Unary                                      128        81     47        81      0 
   unassigned_expression/Unassigned                 133       115     18       115      0 
   undefined_phi_args/Baddie                        324       284     40       284      0 
   unssa/UnSSA                                      452       369     83       369      0 

src/puya/ir/_utils.py

@@ -0,0 +1,17 @@
+from collections import deque
+from collections.abc import Iterator
+
+from puya.ir import models
+
+
+def bfs_block_order(start: models.BasicBlock) -> Iterator[models.BasicBlock]:
+    q = deque[models.BasicBlock]()
+    q.append(start)
+    visited = {start}
+    while q:
+        block = q.popleft()
+        yield block
+        for succ in block.successors:
+            if succ not in visited:
+                q.append(succ)
+                visited.add(succ)

src/puya/ir/builder/blocks.py

@@ -112,13 +112,13 @@ def validate_block_predecessors(self) -> None:
                     non_entry_block.source_location,
                 )
 
-    def activate_block(self, block: BasicBlock, *, ignore_predecessor_check: bool = False) -> None:
+    def activate_block(self, block: BasicBlock) -> None:
         """Add a basic block and make it the active one (target of adds)"""
         if not self.active_block.terminated:
             raise InternalError(
                 "Attempted to activate a new block when current block has not been terminated"
             )
-        if not block.predecessors and not ignore_predecessor_check:
+        if not block.predecessors:
             raise InternalError("Attempted to add a (non-entry) block with no predecessors")
         block.id = len(self._blocks)
         self._blocks.append(block)
@@ -128,6 +128,13 @@ def goto_and_activate(self, block: BasicBlock) -> None:
         self.goto(block)
         self.activate_block(block)
 
+    def try_goto_and_activate(self, block: BasicBlock) -> bool:
+        self.goto(block)
+        if block.predecessors:
+            self.activate_block(block)
+            return True
+        return False
+
     def maybe_add_implicit_subroutine_return(self, params: Sequence[Parameter]) -> None:
         if not self._blocks[-1].terminated:
             self.terminate(