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IR: Drop uniquing for self-referencing MDNodes

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It doesn't make sense to unique self-referencing nodes.  Drop uniquing
for them.

Note that `MDNode::intersect()` occasionally returns self-referencing
nodes.  Previously these would be returned by `MDNode::get()`.  I'm not
convinced this was intended behaviour -- to me it seems it should return
a node whose only operand is the self-reference -- but I don't know much
about alias scopes so I'm preserving it for now.

This is part of PR21532.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223618 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Duncan P. N. Exon Smith
2014-12-07 19:52:06 +00:00
parent 6bb158dd34
commit 7280d8ccce
2 changed files with 55 additions and 1 deletions
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lib/IR/Metadata.cpp
+15 -1
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@@ -353,7 +353,9 @@ void MDNode::replaceOperand(MDNodeOperand *Op, Value *To) {
// anymore. This commonly occurs during destruction, and uniquing these
// brings little reuse. Also, this means we don't need to include
// isFunctionLocal bits in the hash for MDNodes.
if (!To) {
//
// Also drop uniquing if this has a reference to itself.
if (!To || To == this) {
setIsNotUniqued();
return;
}
@@ -406,6 +408,18 @@ MDNode *MDNode::intersect(MDNode *A, MDNode *B) {
}
}
// Handle alias scope self-references specially.
//
// FIXME: This preserves long-standing behaviour, but is it really the right
// behaviour? Or was that an unintended side-effect of node uniquing?
if (!Vals.empty())
if (MDNode *N = dyn_cast_or_null<MDNode>(Vals[0]))
if (N->getNumOperands() == Vals.size() && N == N->getOperand(0)) {
for (unsigned I = 1, E = Vals.size(); I != E; ++I)
if (Vals[I] != N->getOperand(I))
return MDNode::get(A->getContext(), Vals);
return N;
}
return MDNode::get(A->getContext(), Vals);
}