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Linker: Fix references to uniqued nodes after r243883

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r243883 started moving 'distinct' nodes instead of duplicated them in
lib/Linker.  This had the side-effect of sometimes not cloning uniqued
nodes that reference them.  I missed a corner case:

    !named = !{!0}
    !0 = !{!1}
    !1 = distinct !{!0}

!0 is the entry point for "remapping", and a temporary clone (say,
!0-temp) is created and mapped in case we need to model a uniquing
cycle.

    Recursive descent into !1.  !1 is distinct, so we leave it alone,
    but update its operand to !0-temp.

Pop back out to !0.  Its only operand, !1, hasn't changed, so we don't
need to use !0-temp.  !0-temp goes out of scope, and we're finished
remapping, but we're left with:

    !named = !{!0}
    !0 = !{!1}
    !1 = distinct !{null} ; uh oh...

Previously, if !0 and !0-temp ended up with identical operands, then
!0-temp couldn't have been referenced at all.  Now that distinct nodes
don't get duplicated, that assumption is invalid.  We need to
!0-temp->replaceAllUsesWith(!0) before freeing !0-temp.

I found this while running an internal `-flto -g` bootstrap.  Strangely,
there was no case of this in the open source bootstrap I'd done before
commit...

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@243961 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Duncan P. N. Exon Smith 2015-08-04 06:42:31 +00:00
parent 44cb0f3803
commit 81032088a7
2 changed files with 17 additions and 1 deletions
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4
lib/Transforms/Utils/ValueMapper.cpp
View File

@ -258,9 +258,11 @@ static Metadata *mapUniquedNode(const MDNode *Node,
// Create a temporary node upfront in case we have a metadata cycle.
auto ClonedMD = Node->clone();
if (!remap(Node, ClonedMD.get(), Cycles, VM, Flags, TypeMapper, Materializer))
if (!remap(Node, ClonedMD.get(), Cycles, VM, Flags, TypeMapper, Materializer)) {
// No operands changed, so use the identity mapping.
ClonedMD->replaceAllUsesWith(const_cast<MDNode *>(Node));
return mapToSelf(VM, Node);
}
// At least one operand has changed, so uniquify the cloned node.
return mapToMetadata(VM, Node,

14
test/Linker/uniqued-distinct-cycles.ll Normal file
View File

@ -0,0 +1,14 @@
; RUN: llvm-link -o - %s | llvm-dis | FileCheck %s
; CHECK: !named = !{!0, !2}
!named = !{!0, !2}
; CHECK: !0 = !{!1}
; CHECK-NEXT: !1 = distinct !{!0}
!0 = !{!1}
!1 = distinct !{!0}
; CHECK-NEXT: !2 = distinct !{!3}
; CHECK-NEXT: !3 = !{!2}
!2 = distinct !{!3}
!3 = !{!2}