Fix nothrow modeling of have_fma #43785
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oscardssmith
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Jan 12, 2022
vtjnash
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Jan 13, 2022
Allows functions that make use of fma to be considered ConstAPI (so long has both have_fma branches return the same constant).
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aviatesk
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Jan 13, 2022
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| intrinsic_effect_free_if_nothrow(f) = f === Intrinsics.pointerref || | ||
| f === Intrinsics.have_fma || is_pure_intrinsic_infer(f) |
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| intrinsic_effect_free_if_nothrow(f) = f === Intrinsics.pointerref || | |
| f === Intrinsics.have_fma || is_pure_intrinsic_infer(f) | |
| intrinsic_effect_free_if_nothrow(f) = | |
| f === Intrinsics.pointerref || | |
| # in order to allow FMA multiversioning, we exclude `have_fma` from `is_pure_intrinsic_infer` | |
| # because it shouldn't be constant folded at inference time, but we still mark it here | |
| # so that we allow a call with `have_fma` to use the constant calling convention | |
| # when both branches have the same constant value. | |
| f === Intrinsics.have_fma || | |
| is_pure_intrinsic_infer(f) |
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Multiversioning is one of the issues, but it's not exclusive. Everything here that reads implicit runtime state needs to be excluded. If it is not guaranteed to always return bitwise egal output given bitwise egal input, it must be excluded from is_pure_intrinsic_infer. I'm working on a PR to make the effect free code a little more principled, so I'll fold the documentation comment in there.
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Allows functions that make use of fma to be considered ConstAPI (so long has both have_fma branches return the same constant).
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Allows functions that make use of fma to be considered ConstAPI (so long has both have_fma branches return the same constant).
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Allows functions that make use of fma to be considered ConstAPI (so long has both have_fma branches return the same constant).
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Allows functions that make use of fma to be considered ConstAPI (so long has both have_fma branches return the same constant).
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Allows functions that make use of fma to be considered ConstAPI
(so long has both have_fma branches return the same constant).
cc @ianatol