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[Miscompile] Tuple == / != repeats, skips and reorders side effects in its operands #3797
Description
Kind: Miscompile in the shared pipeline: every QIR profile that accepts the program returns a wrong value.
Affects: every profile
Found in: vs_sim.min_tuple_eq_call_twice.c33264e422, vs_sim.min_tuple_eq_short_circuit.1349fb306c
Bump(q) == (One, 5) should call Bump once. The lowered comparison compares element by
element and evaluates Bump(q) once per element, so X is applied twice and the qubit ends in
Zero.
Q#
operation Bump(q : Qubit) : (Result, Int) {
X(q);
(M(q), 5)
}
operation Main() : Result {
use q = Qubit();
let _ = Bump(q) == (One, 5);
MResetZ(q)
}Outputs
10 shots each. The simulator runs the Q# program directly; each profile compiles it to QIR, which is run with qir-runner.
| Run | Output | Correct? |
|---|---|---|
| Simulator | 1 |
yes |
| Base | rejected (Qdk.Qsc.CapabilitiesCk.UseOfDynamicBool) |
n/a |
| Adaptive_RI | 0 |
no |
| Adaptive_RIF | 0 |
no |
| Adaptive | 0 |
no |
| Correct output | 1 |
Correct output
Bump runs once, so the qubit is flipped once and measures One.
Other shapes
The element-wise comparison also short-circuits. Here the first elements differ, so
MResetZ(b) is never evaluated and b stays One. The simulator returns 0 and every
profile returns 1:
operation Main() : Result {
use a = Qubit();
use b = Qubit();
X(b);
let _ = (MResetZ(a), MResetZ(b)) == (One, Zero);
MResetZ(b)
}Probable cause
tuple_compare_lower rewrites lhs == rhs into a chain of element comparisons joined with
and (or for !=) (qsc_fir_transforms/src/tuple_compare_lower.rs:158-243). An operand
that isn't a tuple literal is accessed once per element (extract_or_field), so it is evaluated
once per element, and the and/or chain short-circuits elements that should all be evaluated.
Operands with side effects need to be bound to temporaries first.
Reproduce
"""Tuple `==` / `!=` repeats, skips and reorders side effects in its operands
Compiles the Q# program below to QIR for each target profile, runs that QIR with
qir-runner, and runs the same program in the Q# simulator for comparison.
Exits 0 while the bug reproduces: Base, Adaptive_RI, Adaptive_RIF and Adaptive return something other than 1.
Requires: pip install qdk qirrunner
"""
import os
import re
import sys
import tempfile
import qirrunner
from qdk import Context, TargetProfile
SOURCE = """
operation Bump(q : Qubit) : (Result, Int) {
X(q);
(M(q), 5)
}
operation Main() : Result {
use q = Qubit();
let _ = Bump(q) == (One, 5);
MResetZ(q)
}
"""
ENTRY = "Main()"
EXPECTED = "1" # the correct output
AFFECTED = ['Base', 'Adaptive_RI', 'Adaptive_RIF', 'Adaptive'] # runs that show the bug
SHOTS = 10
PROFILES = ["Base", "Adaptive_RI", "Adaptive_RIF", "Adaptive"]
def fmt(value):
"""Formats a simulator value the same way as qir-runner output below."""
if value is None:
return "()"
if type(value).__name__ == "Result":
return "1" if str(value).endswith("One") else "0"
if isinstance(value, bool):
return str(value).lower()
if isinstance(value, float):
return repr(value)
if isinstance(value, (tuple, list)):
inner = ", ".join(fmt(v) for v in value)
return f"({inner})" if isinstance(value, tuple) else f"[{inner}]"
return str(value)
def parse_shots(text):
"""Turns qir-runner's output records into one formatted value per shot."""
shots, records = [], None
for line in text.splitlines():
fields = line.split("\t")
if fields[0] == "START":
records = []
elif fields[0] == "OUTPUT" and records is not None:
records.append((fields[1], fields[2]))
elif fields[0] == "END" and records is not None:
shots.append(to_text(iter(records)) if records else "()")
if fields[1] != "0":
shots[-1] = f"exit code {fields[1]}"
records = None
return shots
def to_text(records):
kind, value = next(records)
if kind in ("TUPLE", "ARRAY"):
inner = ", ".join(to_text(records) for _ in range(int(value)))
return f"({inner})" if kind == "TUPLE" else f"[{inner}]"
if kind == "DOUBLE":
return repr(float(value))
if kind == "BOOL":
return value.lower()
return value
def run_qir(qir):
with tempfile.NamedTemporaryFile("w", suffix=".ll", delete=False) as file:
file.write(qir)
handler = qirrunner.OutputHandler()
try:
qirrunner.run(file.name, shots=SHOTS, rng_seed=1, output_fn=handler.handle)
except Exception as error: # qir-runner rejects the module
message = str(error).strip().splitlines()[0]
if message.startswith("Failed to link"): # valid QIR calling functions qir-runner lacks
return {"qir-runner can't link: " + message.split(": ", 1)[-1]}
return {"invalid QIR: " + re.sub(r"^\S+\.ll:\d+:\d+: (error: )?", "", message)}
finally:
os.unlink(file.name)
return set(parse_shots(handler.get_output()))
def outputs():
rows = {}
ctx = Context(target_profile=TargetProfile.Unrestricted)
ctx.eval(SOURCE)
rows["simulator"] = {fmt(v) for v in ctx.run(ENTRY, SHOTS, seed=1)}
for profile in PROFILES:
ctx = Context(target_profile=getattr(TargetProfile, profile))
try:
ctx.eval(SOURCE)
qir = str(ctx.compile(ENTRY))
except Exception as error: # the profile rejects the program
rows[profile] = {"does not compile: " + str(error).strip().splitlines()[0]}
continue
rows[profile] = run_qir(qir)
return rows
def main():
rows = outputs()
width = max(map(len, rows)) + 2
for name, values in rows.items():
print(f"{name:<{width}}{' | '.join(sorted(values))}")
print(f"{'expected':<{width}}{EXPECTED}")
wrong = [name for name in AFFECTED if name in rows and rows[name] != {EXPECTED}]
if wrong:
print(f"REPRODUCED: {', '.join(wrong)} differ from {EXPECTED}")
return 0
print("NOT REPRODUCED")
return 1
if __name__ == "__main__":
sys.exit(main())
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