this breaks if we don't drop the ELSE region when cond==false

test_false_no_else.py

from xdsl.context import Context
from xdsl.dialects import scf, arith, func, builtin
from xdsl.dialects.builtin import ModuleOp
from xdsl.ir import Block, Region
from xdsl.transforms.canonicalization_patterns.scf import IfPropagateConstantCondition
from xdsl.pattern_rewriter import PatternRewriteWalker

ctx = Context()
ctx.load_dialect(scf.Scf)
ctx.load_dialect(arith.Arith)
ctx.load_dialect(func.Func)
ctx.load_dialect(builtin.Builtin)


false_val = arith.ConstantOp.from_int_and_width(0, 1)
val_1 = arith.ConstantOp.from_int_and_width(1, 32)

true_block = Block([val_1, scf.YieldOp(val_1)])
true_region = Region(true_block)
if_op = scf.IfOp(false_val, [], true_region) # no else region

func_body = Region(Block([false_val, if_op, func.ReturnOp()]))
func_op = func.FuncOp("test_false_no_else", ([], []), func_body)

module = ModuleOp([func_op])


print("\nbefore:\n")
print(module)

# builtin.module {
#   func.func @test_false_no_else() {
#     %0 = arith.constant false
#     scf.if %0 {
#       %1 = arith.constant 1 : i32
#     }
#     func.return
#   }
# }

walker = PatternRewriteWalker(IfPropagateConstantCondition()) # avoid DCE
walker.rewrite_module(module)

print("\nafter:\n")
print(module)

# builtin.module {
#   func.func @test_false_no_else() {
#     %0 = arith.constant false
#     func.return
#   }
# }