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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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16
lib/IR/Metadata.cpp
View File

@ -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);
}

40
unittests/IR/MetadataTest.cpp
View File

@ -123,6 +123,46 @@ TEST_F(MDNodeTest, Delete) {
delete I;
}
TEST_F(MDNodeTest, SelfReference) {
// !0 = metadata !{metadata !0}
// !1 = metadata !{metadata !0}
{
MDNode *Temp = MDNode::getTemporary(Context, None);
Value *Args[] = {Temp};
MDNode *Self = MDNode::get(Context, Args);
Self->replaceOperandWith(0, Self);
MDNode::deleteTemporary(Temp);
ASSERT_EQ(Self, Self->getOperand(0));
// Self-references should be distinct, so MDNode::get() should grab a
// uniqued node that references Self, not Self.
Args[0] = Self;
MDNode *Ref1 = MDNode::get(Context, Args);
MDNode *Ref2 = MDNode::get(Context, Args);
EXPECT_NE(Self, Ref1);
EXPECT_EQ(Ref1, Ref2);
}
// !0 = metadata !{metadata !0, metadata !{}}
// !1 = metadata !{metadata !0, metadata !{}}
{
MDNode *Temp = MDNode::getTemporary(Context, None);
Value *Args[] = {Temp, MDNode::get(Context, None)};
MDNode *Self = MDNode::get(Context, Args);
Self->replaceOperandWith(0, Self);
MDNode::deleteTemporary(Temp);
ASSERT_EQ(Self, Self->getOperand(0));
// Self-references should be distinct, so MDNode::get() should grab a
// uniqued node that references Self, not Self itself.
Args[0] = Self;
MDNode *Ref1 = MDNode::get(Context, Args);
MDNode *Ref2 = MDNode::get(Context, Args);
EXPECT_NE(Self, Ref1);
EXPECT_EQ(Ref1, Ref2);
}
}
TEST(NamedMDNodeTest, Search) {
LLVMContext Context;
Constant *C = ConstantInt::get(Type::getInt32Ty(Context), 1);