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Backport LLVM apfloat commit to rustc_apfloat

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Backports LLVM commit: e34bd1e0b0

Fixes #69532
This commit is contained in:
est31 2020-09-30 17:46:18 +02:00
parent c6e4db620a
commit 7f5008c829
3 changed files with 45 additions and 0 deletions
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12
compiler/rustc_apfloat/src/ieee.rs
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@ -1511,6 +1511,18 @@ impl<S: Semantics, T: Semantics> FloatConvert<IeeeFloat<T>> for IeeeFloat<S> {
sig::set_bit(&mut r.sig, T::PRECISION - 1);
}
// If we are truncating NaN, it is possible that we shifted out all of the
// set bits in a signalling NaN payload. But NaN must remain NaN, so some
// bit in the significand must be set (otherwise it is Inf).
// This can only happen with sNaN. Set the 1st bit after the quiet bit,
// so that we still have an sNaN.
if r.sig[0] == 0 {
assert!(shift < 0, "Should not lose NaN payload on extend");
assert!(T::PRECISION >= 3, "Unexpectedly narrow significand");
assert!(*loses_info, "Missing payload should have set lost info");
sig::set_bit(&mut r.sig, T::PRECISION - 3);
}
// gcc forces the Quiet bit on, which means (float)(double)(float_sNan)
// does not give you back the same bits. This is dubious, and we
// don't currently do it. You're really supposed to get