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Differential D45190

[LangRef] fix description and examples of fptrunc
ClosedPublic

Authored by spatel on Apr 2 2018, 3:49 PM.

Details

Reviewers
efriedma
scanon
nagisa
Commits
rGd96a363855f9: [LangRef] fix description and examples of fptrunc
rL329065: [LangRef] fix description and examples of fptrunc
Summary

As noted in PR36966:
https://bugs.llvm.org/show_bug.cgi?id=36966

The old description doesn't match what we do in code, so this just fixes the documentation to avoid confusion.

Diff Detail

Event Timeline

spatel created this revision.Apr 2 2018, 3:49 PM
Herald added a subscriber: mcrosier. · View Herald TranscriptApr 2 2018, 3:49 PM
efriedma accepted this revision.Apr 2 2018, 4:48 PM

LGTM

This revision is now accepted and ready to land.Apr 2 2018, 4:48 PM
Closed by commit rL329065: [LangRef] fix description and examples of fptrunc (authored by spatel). · Explain WhyApr 3 2018, 6:09 AM
This revision was automatically updated to reflect the committed changes.

Revision Contents

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docs/LangRef.rst

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The size of ``value`` must be larger than the size of ``ty2``. This The size of ``value`` must be larger than the size of ``ty2``. This
implies that ``fptrunc`` cannot be used to make a *no-op cast*. implies that ``fptrunc`` cannot be used to make a *no-op cast*.
Semantics: Semantics:
"""""""""" """"""""""
The '``fptrunc``' instruction casts a ``value`` from a larger The '``fptrunc``' instruction casts a ``value`` from a larger
:ref:`floating-point <t_floating>` type to a smaller :ref:`floating-point :ref:`floating-point <t_floating>` type to a smaller :ref:`floating-point
<t_floating>` type. If the value cannot fit (i.e. overflows) within the <t_floating>` type.
destination type, ``ty2``, then the results are undefined. If the cast produces This instruction is assumed to execute in the default :ref:`floating-point
an inexact result, how rounding is performed (e.g. truncation, also known as environment <floatenv>`.
round to zero) is undefined.
Example: Example:
"""""""" """"""""
.. code-block:: llvm .. code-block:: llvm
%X = fptrunc double 123.0 to float ; yields float:123.0 %X = fptrunc double 16777217.0 to float ; yields float:16777216.0
%Y = fptrunc double 1.0E+300 to float ; yields undefined %Y = fptrunc double 1.0E+300 to half ; yields half:+infinity
'``fpext .. to``' Instruction '``fpext .. to``' Instruction
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Syntax: Syntax:
""""""" """""""
:: ::
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