FA-11446 / Compiler transformation correctness / Open access

Dead-result elimination deletes a volatile read · case 01

Dead-result elimination deletes a volatile read.

Verified by executionVariant 1 · 7 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

Result liveness is treated as the only reason to retain an instruction.

VERIFIED REPAIR

Retain unused instructions with any modeled observable effect.

Unsuccessful approach: Retaining writes alone still removes volatile reads and trapping instructions.

Case contract

Return retained instruction IDs in order. Instructions have (id, live, effect), where effect is pure, write, volatile or trap; only unused pure operations may be removed.

Why this case matters

A deterministic miniature compiler-pass model; inputs are explicit IR facts, not a production compiler.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(ops):
    return [i for i, live, effect in ops if live]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('empty', solve([]), [])
check('dead pure', solve([(N,False,'pure')]), [])
check('live pure', solve([(N,True,'pure')]), [N])
check('write', solve([(N,False,'write')]), [N])
check('volatile', solve([(N,False,'volatile')]), [N])
check('trap', solve([(N,False,'trap')]), [N])
check('preserve order', solve([(N,False,'write'),(N+1,False,'pure'),(N+2,True,'pure')]), [N,N+2])
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
empty	`[]`	`[]`	Passed
dead pure	`[]`	`[]`	Passed
live pure	`[1]`	`[1]`	Passed
write	`[]`	`[1]`	Failed
volatile	`[]`	`[1]`	Failed
trap	`[]`	`[1]`	Failed
preserve order	`[3]`	`[1, 3]`	Failed

SHA-256 / 12ba8d22515b8d8bcd0ea135e98ece94363b6c25c0310a2216054e04ce6f8379

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(ops):
    return [i for i, live, effect in ops if live or effect == 'write']
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('empty', solve([]), [])
check('dead pure', solve([(N,False,'pure')]), [])
check('live pure', solve([(N,True,'pure')]), [N])
check('write', solve([(N,False,'write')]), [N])
check('volatile', solve([(N,False,'volatile')]), [N])
check('trap', solve([(N,False,'trap')]), [N])
check('preserve order', solve([(N,False,'write'),(N+1,False,'pure'),(N+2,True,'pure')]), [N,N+2])
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
empty	`[]`	`[]`	Passed
dead pure	`[]`	`[]`	Passed
live pure	`[1]`	`[1]`	Passed
write	`[1]`	`[1]`	Passed
volatile	`[]`	`[1]`	Failed
trap	`[]`	`[1]`	Failed
preserve order	`[1, 3]`	`[1, 3]`	Passed

SHA-256 / 318f6512259e87a43ed423e182e3d96c9d4603df2cee667e6aadae5b6969b4dd

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(ops):
    return [i for i, live, effect in ops if live or effect != 'pure']
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('empty', solve([]), [])
check('dead pure', solve([(N,False,'pure')]), [])
check('live pure', solve([(N,True,'pure')]), [N])
check('write', solve([(N,False,'write')]), [N])
check('volatile', solve([(N,False,'volatile')]), [N])
check('trap', solve([(N,False,'trap')]), [N])
check('preserve order', solve([(N,False,'write'),(N+1,False,'pure'),(N+2,True,'pure')]), [N,N+2])
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
empty	`[]`	`[]`	Passed
dead pure	`[]`	`[]`	Passed
live pure	`[1]`	`[1]`	Passed
write	`[1]`	`[1]`	Passed
volatile	`[1]`	`[1]`	Passed
trap	`[1]`	`[1]`	Passed
preserve order	`[1, 3]`	`[1, 3]`	Passed

SHA-256 / 30ec2de7270341d84e870433827d5f0b55a96098a27cd3ebdbd3df31b6823374

Verification & scope

This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:38:48.025717+00:00.

Case digest / 83e496caa01906478df7f3e9926a8b58a66caf359e0f49401f9c3ea8fd7a219d