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[LangRef] Drop misleading anecdote

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`shl nsw i8 1, i8 8` is poison, but `mul i8 1, i8 128` is not.

This was discussed previously here:
http://lists.llvm.org/pipermail/llvm-dev/2015-April/084195.html.  From
the discussion, it was not clear which semantics we want for `shl`, but
for now at least make the language reference more accurate.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@286785 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Sanjoy Das 2016-11-13 23:40:40 +00:00
parent 5b20442fc2
commit 00eb18da3b
1 changed files with 1 additions and 3 deletions
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@ -6430,9 +6430,7 @@ If the ``nuw`` keyword is present, then the shift produces a :ref:`poison
value <poisonvalues>` if it shifts out any non-zero bits. If the
``nsw`` keyword is present, then the shift produces a :ref:`poison
value <poisonvalues>` if it shifts out any bits that disagree with the
resultant sign bit. As such, NUW/NSW have the same semantics as they
would if the shift were expressed as a mul instruction with the same
nsw/nuw bits in (mul %op1, (shl 1, %op2)).
resultant sign bit.
Example:
""""""""