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Make it possible to indicate relaxed floating point requirements at the IR level

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through the use of 'fpmath' metadata.  Currently this only provides a 'fpaccuracy'
value, which may be a number in ULPs or the keyword 'fast', however the intent is
that this will be extended with additional information about NaN's, infinities
etc later.  No optimizations have been hooked up to this so far.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@154822 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Duncan Sands
2012-04-16 16:28:59 +00:00
parent 9e67db4af1
commit 8883c43ddc
10 changed files with 282 additions and 86 deletions
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19
docs/LangRef.html
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@@ -3006,10 +3006,12 @@ call void @llvm.dbg.value(metadata !24, i64 0, metadata !25)
<div>
<p><tt>fpmath</tt> metadata may be attached to any instruction of floating point
type. It can be used to express the maximum acceptable relative error in the
result of that instruction, in ULPs, thus potentially allowing the compiler
to use a more efficient but less accurate method of computing it.
ULP is defined as follows:</p>
type. It can be used to express the maximum acceptable error in the result of
that instruction, in ULPs, thus potentially allowing the compiler to use a
more efficient but less accurate method of computing it. The number of ULPs
may also be the string <tt>"fast"</tt>, which tells the compiler that speed
matters more than accuracy, so any fairly accurate method of computation is
fine as long as it is quick. ULP is defined as follows:</p>
<blockquote>
@@ -3021,13 +3023,14 @@ call void @llvm.dbg.value(metadata !24, i64 0, metadata !25)
</blockquote>
<p>The metadata node shall consist of a single non-negative floating
point number representing the maximum relative error. For example,
2.5 ULP:</p>
<p>The metadata node shall consist of a single positive floating point number
representing the maximum relative error, or the string <tt>"fast"</tt>.
For example:</p>
<div class="doc_code">
<pre>
!0 = metadata !{ float 2.5 }
!0 = metadata !{ float 2.5 } ; maximum acceptable inaccuracy is 2.5 ULPs
!1 = metadata !{ !metadata !"fast" } ; potentially unbounded inaccuracy
</pre>
</div>