Include CPU ISA hash in Warp kernel cache key

.github/workflows/ci.yml

@@ -121,6 +121,10 @@ jobs:
         uses: actions/setup-python@a309ff8b426b58ec0e2a45f0f869d46889d02405  # v6.2.0
         with:
           python-version-file: ".python-version"
+      - name: Detect CPU ISA features for cache key
+        id: cpu-id
+        shell: bash
+        run: echo "cpu-hash=$(python3 scripts/ci/cpu_isa_hash.py)" >> "$GITHUB_OUTPUT"
       - name: Restore Warp kernel cache
         if: github.event_name != 'merge_group'
         uses: actions/cache@668228422ae6a00e4ad889ee87cd7109ec5666a7  # v5.0.4
@@ -129,9 +133,9 @@ jobs:
             ~/.cache/warp
             ~/Library/Caches/warp
             ~\AppData\Local\NVIDIA\warp\Cache
-          key: warp-kernels-${{ runner.os }}-${{ runner.arch }}-${{ hashFiles('uv.lock', 'newton/**/*.py') }}
+          key: warp-kernels-${{ runner.os }}-${{ runner.arch }}-${{ steps.cpu-id.outputs.cpu-hash }}-${{ hashFiles('uv.lock', 'newton/**/*.py') }}
           restore-keys: |
-            warp-kernels-${{ runner.os }}-${{ runner.arch }}-
+            warp-kernels-${{ runner.os }}-${{ runner.arch }}-${{ steps.cpu-id.outputs.cpu-hash }}-
       - name: Run Tests
         run: uv run --extra dev -m newton.tests --no-cache-clear --junit-report-xml rspec.xml --coverage --coverage-xml coverage.xml
       - name: Test Summary

scripts/ci/cpu_isa_hash.py

@@ -0,0 +1,114 @@
+#!/usr/bin/env python3
+# SPDX-FileCopyrightText: Copyright (c) 2026 The Newton Developers
+# SPDX-License-Identifier: Apache-2.0
+
+"""Print a short hash of the host CPU's ISA feature set.
+
+Warp 1.13+ compiles CPU kernels with ``-march=native``, so cached object
+files are only safe to reuse on a CPU with the same instruction set.
+This script detects the ISA features and prints a 16-character hex hash
+suitable for use in a CI cache key.
+
+Supported platforms:
+  - x86_64 Linux / macOS / Windows (via system C compiler)
+  - AArch64 Linux (via /proc/cpuinfo)
+  - AArch64 macOS (via sysctl)
+"""
+
+import hashlib
+import platform
+import subprocess
+import sys
+
+# ISA-related macro keywords emitted by ``cc -march=native -dM -E``.
+# These correspond to the instruction set extensions that affect codegen.
+_X86_ISA_KEYWORDS = (
+    "ADX",
+    "AES",
+    "AVX",
+    "BMI",
+    "CLFLUSH",
+    "F16C",
+    "FMA",
+    "LZCNT",
+    "MMX",
+    "MOVBE",
+    "PCLMUL",
+    "POPCNT",
+    "RDRAND",
+    "RDSEED",
+    "SHA",
+    "SSE",
+    "VAES",
+    "VPCLMUL",
+)
+
+
+def _x86_features() -> str:
+    """Query ISA features by asking the system C compiler what -march=native enables."""
+    for cc in ("cc", "gcc", "clang"):
+        try:
+            out = subprocess.check_output(
+                [cc, "-march=native", "-dM", "-E", "-x", "c", "-"],
+                input="",
+                text=True,
+                stderr=subprocess.DEVNULL,
+            )
+        except (FileNotFoundError, subprocess.CalledProcessError):
+            continue
+
+        macros = sorted(
+            line.split()[1]
+            for line in out.splitlines()
+            if line.startswith("#define __") and any(k in line for k in _X86_ISA_KEYWORDS)
+        )
+        if macros:
+            return " ".join(macros)
+
+    return ""
+
+
+def _aarch64_features() -> str:
+    """Query ISA features from /proc/cpuinfo (Linux) or sysctl (macOS)."""
+    # Linux: kernel exposes HWCAP flags in /proc/cpuinfo.
+    try:
+        with open("/proc/cpuinfo") as f:
+            for line in f:
+                if line.startswith("Features"):
+                    return " ".join(sorted(line.split(":")[1].split()))
+    except FileNotFoundError:
+        pass
+
+    # macOS: sysctl exposes CPU features.
+    try:
+        out = subprocess.check_output(
+            ["sysctl", "-n", "machdep.cpu.features"],
+            text=True,
+            stderr=subprocess.DEVNULL,
+        )
+        if out.strip():
+            return " ".join(sorted(out.strip().split()))
+    except (FileNotFoundError, subprocess.CalledProcessError):
+        pass
+
+    return ""
+
+
+def get_features() -> str:
+    machine = platform.machine().lower()
+    if machine in ("x86_64", "amd64", "x86", "i686"):
+        return _x86_features()
+    if machine in ("aarch64", "arm64"):
+        return _aarch64_features()
+    return ""
+
+
+def main() -> None:
+    features = get_features() or platform.processor()
+    h = hashlib.sha256(features.encode()).hexdigest()[:16]
+    print(f"features: {features}", file=sys.stderr)
+    print(h)
+
+
+if __name__ == "__main__":
+    main()