[llvm] r329065 - [LangRef] fix description and examples of fptrunc

[Sanjay Patel via llvm-commits]

Author: spatel
Date: Tue Apr  3 06:05:20 2018
New Revision: 329065

URL: http://llvm.org/viewvc/llvm-project?rev=329065&view=rev
Log:
[LangRef] fix description and examples of fptrunc

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.

Differential Revision: https://reviews.llvm.org/D45190

Modified:
    llvm/trunk/docs/LangRef.rst

Modified: llvm/trunk/docs/LangRef.rst
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/LangRef.rst?rev=329065&r1=329064&r2=329065&view=diff
==============================================================================
--- llvm/trunk/docs/LangRef.rst (original)
+++ llvm/trunk/docs/LangRef.rst Tue Apr  3 06:05:20 2018
@@ -8371,18 +8371,17 @@ Semantics:
 
 The '``fptrunc``' instruction casts a ``value`` from a larger
 :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
-destination type, ``ty2``, then the results are undefined. If the cast produces
-an inexact result, how rounding is performed (e.g. truncation, also known as
-round to zero) is undefined.
+<t_floating>` type.  
+This instruction is assumed to execute in the default :ref:`floating-point
+environment <floatenv>`.
 
 Example:
 """"""""
 
 .. code-block:: llvm
 
-      %X = fptrunc double 123.0 to float         ; yields float:123.0
-      %Y = fptrunc double 1.0E+300 to float      ; yields undefined
+      %X = fptrunc double 16777217.0 to float    ; yields float:16777216.0
+      %Y = fptrunc double 1.0E+300 to half       ; yields half:+infinity
 
 '``fpext .. to``' Instruction
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^