transforms.cfg_simplifier: handle phi and branch_if properly.

artiq/compiler/transforms/cfg_simplifier.py

@@ -18,5 +18,15 @@ class CFGSimplifier:
             if len(block.instructions) == 1 and \
                     isinstance(block.terminator(), ir.Branch):
                 successor, = block.successors()
+
+                for insn in set(block.uses):
+                    if isinstance(insn, ir.BranchIf) and \
+                            ((insn.if_true() == block and insn.if_false() == successor) or
+                             (insn.if_true() == successor and insn.if_false() == block)):
+                        # Our IR doesn't tolerate branch_if %c, %b, %b
+                        insn.replace_with(ir.Branch(successor))
+                    elif isinstance(insn, ir.Phi):
+                        insn.remove_incoming_block(block)
+
                 block.replace_all_uses_with(successor)
                 block.erase()