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Stub out a new updating interface to AliasAnalysis, allowing stateful analyses to be informed when

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a pointer value has potentially become escaping.  Implementations can choose to either fall back to
conservative responses for that value, or may recompute their analysis to accomodate the change.

llvm-svn: 122777
This commit is contained in:
Owen Anderson 2011-01-03 21:38:41 +00:00
parent 658a5c2101
commit a52e5dbdfa
3 changed files with 40 additions and 1 deletions
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24
docs/AliasAnalysis.html
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@ -464,7 +464,7 @@ analysis results updated to reflect the changes made by these transformations.
</p>
<p>
The <tt>AliasAnalysis</tt> interface exposes three methods which are used to
The <tt>AliasAnalysis</tt> interface exposes four methods which are used to
communicate program changes from the clients to the analysis implementations.
Various alias analysis implementations should use these methods to ensure that
their internal data structures are kept up-to-date as the program changes (for
@ -505,6 +505,28 @@ value, then deleting the old value. This method cannot be overridden by alias
analysis implementations.
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">The <tt>addEscapingUse</tt> method</div>
<div class="doc_text">
<p>The <tt>addEscapingUse</tt> method is used when the uses of a pointer
value have changed in ways that may invalidate precomputed analysis information.
Implementations may either use this callback to provide conservative responses
for points whose uses have change since analysis time, or may recompute some
or all of their internal state to continue providing accurate responses.</p>
<p>In general, any new use of a pointer value is considered an escaping use,
and must be reported through this callback, <em>except</em> for the
uses below:</p>
<ul>
<li>A <tt>bitcast</tt> or <tt>getelementptr</tt> of the pointer</li>
<li>A <tt>store</tt> through the pointer (but not a <tt>store</tt>
<em>of</em> the pointer)</li>
<li>A <tt>load</tt> through the pointer</li>
</ul>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="implefficiency">Efficiency Issues</a>

11
include/llvm/Analysis/AliasAnalysis.h
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@ -469,6 +469,17 @@ public:
///
virtual void copyValue(Value *From, Value *To);
/// addEscapingUse - This method should be used whenever an escaping use is
/// added to a pointer value. Analysis implementations may either return
/// conservative responses for that value in the future, or may recompute
/// some or all internal state to continue providing precise responses.
///
/// Escaping uses are considered by anything _except_ the following:
/// - GEPs or bitcasts of the pointer
/// - Loads through the pointer
/// - Stores through (but not of) the pointer
virtual void addEscapingUse(Use &U);
/// replaceWithNewValue - This method is the obvious combination of the two
/// above, and it provided as a helper to simplify client code.
///

6
lib/Analysis/AliasAnalysis.cpp
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@ -65,6 +65,12 @@ void AliasAnalysis::copyValue(Value *From, Value *To) {
AA->copyValue(From, To);
}
void AliasAnalysis::addEscapingUse(Use &U) {
assert(AA && "AA didn't call InitializeAliasAnalysis in its run method!");
AA->addEscapingUse(U);
}
AliasAnalysis::ModRefResult
AliasAnalysis::getModRefInfo(ImmutableCallSite CS,
const Location &Loc) {