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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

Repository
rL LLVM

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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llvm/
trunk/
docs/
11 lines

Diff 140768

llvm/trunk/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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