MLIR passage 1: LLVM poison-flagged zero counts

// Inputs for the loom-llvm-arith-to-arith mechanical raising stage.
//
// Each sample is a module of llvm.func callables whose bodies mix LLVM
// leading/trailing zero-count intrinsics carrying either is_zero_poison
// setting with ordinary integer LLVM computations.  Operand and result
// types are exact standard numeric types (signless integers and
// fixed-shape vectors of them), so type exactness never by itself blocks
// the mechanical spelling.  Enclosing callables optionally state
// importer-owned passthrough function attributes.

start: {new NFUN = random.randint(1, 3); new F = 0}
       'module {\n' funcs '}\n';

funcs: (F < NFUN) func {F += 1} funcs
     | (F == NFUN) '';

func: {new TY = random.choice(['i32', 'i8', 'i16', 'i64', 'vector<4xi32>', 'vector<2xi64>']); new NOPS = random.randint(1, 4); new K = 0}
      'llvm.func @zero_counts_' fname '(%arg0: ' ty ')' fattrs ' {\n'
      body
      '  llvm.return\n}\n';

fname: [str(F)];

ty: [TY];

kidx: [str(K)];

fattrs: ''
      | ' attributes {passthrough = ["nounwind"]}'
      | ' attributes {passthrough = ["strictfp"]}'
      | ' attributes {passthrough = [["no-trapping-math", "true"]], target_cpu = "generic"}';

body: (K < NOPS) op {K += 1} body
    | (K == NOPS) '';

op: count_op
  | count_op_flagged
  | binary_op;

// Zero-count intrinsic with a freely sampled poison-on-zero contract.
count_op: '  %v' kidx ' = "llvm.intr.' zkind '"(%arg0) <{is_zero_poison = ' poison_flag '}> : (' ty ') -> ' ty '\n';

// Same construct, sampled so that the poison-flagged form stays frequent.
count_op_flagged: '  %v' kidx ' = "llvm.intr.' zkind '"(%arg0) <{is_zero_poison = true}> : (' ty ') -> ' ty '\n';

binary_op: '  %v' kidx ' = llvm.add %arg0, %arg0 : ' ty '\n'
         | '  %v' kidx ' = llvm.mul %arg0, %arg0 : ' ty '\n'
         | '  %v' kidx ' = llvm.and %arg0, %arg0 : ' ty '\n';

zkind: 'ctlz' | 'cttz';

poison_flag: 'true' | 'false';