Fix double-promotion in rsqrt for reduced-precision types

[perheld]

Keep the bfloat16/fp16 rsqrt helper in float precision so Zephyr’s -Wdouble-promotion (treated as an error) no longer fires when ExecuTorch is built for Cortex-M targets.

Signed-off-by: per.held@arm.com
Change-Id: I8fbcc99d8aebac67c4164f2ad502e9b3081386b4

cc @freddan80 @per @zingo @oscarandersson8218 @digantdesai

[pytorch-bot]

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❌ 3 New Failures, 4 Unrelated Failures

As of commit 128e2a8 with merge base cdc2701 ():

NEW FAILURES - The following jobs have failed:

• check-c10-sync / check-c10-sync (gh)
  Process completed with exit code 1.
• pull / unittest-arm-backend-with-no-fvp (test_pytest_ops) / linux-job (gh)
  RuntimeError: Command docker exec -t faa9800e4aa16e096862ac56d144e3cee5c1e96d8ef2574ec0456490b1ade839 /exec failed with exit code 1
• trunk / test-arm-backend (test_pytest_ops_ethosu_fvp) / linux-job (gh)
  RuntimeError: Command docker exec -t f42dabc9d20b96eb29efb6fafcf7386362f47bb1aaaad3ad24e036c20993dfc3 /exec failed with exit code 1

BROKEN TRUNK - The following jobs failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• pull / test-binary-size-linux-gcc / linux-job (gh) (trunk failure)
  ##[error]The operation was canceled.
• pull / test-openvino-linux / linux-job (gh) (trunk failure)
  ##[error]The operation was canceled.
• pull / test-setup-linux-gcc / linux-job (gh) (trunk failure)
  ##[error]The operation was canceled.

UNSTABLE - The following job is marked as unstable, possibly due to flakiness on trunk:

• pull / android / run-emulator (gh) (#16137)
  Timeout waiting for emulator to boot.

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[perheld]

@digantdesai is c10 something that is copied from pytorch and needs fixing upstream there if there is a needed change?

[zingo]

Hi @SS-JIA / @swolchok is this something we want to do or if from PyTorch maybe we rather not touch it?

And if fixed maybe this can be removed from the file:

C10_CLANG_DIAGNOSTIC_PUSH()
#if C10_CLANG_HAS_WARNING("-Wimplicit-float-conversion")
C10_CLANG_DIAGNOSTIC_IGNORE("-Wimplicit-float-conversion")
#endif