[ThinLTO] Keep available_externally symbols live
Summary:
This change fixes PR36483. The bug was originally introduced by a change
that marked non-prevailing symbols dead. This broke LowerTypeTests
handling of available_externally functions, which are non-prevailing.
LowerTypeTests uses liveness information to avoid emitting thunks for
unused functions.
Marking available_externally functions dead is incorrect, the functions
are used though the function definitions are not. This change keeps them
live, and lets the EliminateAvailableExternally/GlobalDCE passes remove
them later instead.
I've also enabled EliminateAvailableExternally for all optimization
levels, I believe it being disabled for O1 was an oversight.
Reviewers: pcc, tejohnson
Reviewed By: tejohnson
Subscribers: grimar, mehdi_amini, inglorion, eraman, llvm-commits
Differential Revision: https://reviews.llvm.org/D43690
llvm-svn: 327041
diff --git a/llvm/lib/Transforms/IPO/FunctionImport.cpp b/llvm/lib/Transforms/IPO/FunctionImport.cpp
index b68058c..c106f11 100644
--- a/llvm/lib/Transforms/IPO/FunctionImport.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionImport.cpp
@@ -544,9 +544,25 @@
if (S->isLive())
return;
- // We do not keep live symbols that are known to be non-prevailing.
- if (isPrevailing(VI.getGUID()) == PrevailingType::No)
- return;
+ // We only keep live symbols that are known to be non-prevailing if any are
+ // available_externally. Those symbols are discarded later in the
+ // EliminateAvailableExternally pass and setting them to not-live breaks
+ // downstreams users of liveness information (PR36483).
+ if (isPrevailing(VI.getGUID()) == PrevailingType::No) {
+ bool AvailableExternally = false;
+ for (auto &S : VI.getSummaryList())
+ if (S->linkage() == GlobalValue::AvailableExternallyLinkage)
+ AvailableExternally = true;
+
+ if (!AvailableExternally)
+ return;
+
+#ifndef NDEBUG
+ for (auto &S : VI.getSummaryList())
+ assert(!GlobalValue::isInterposableLinkage(S->linkage()) &&
+ "Symbol with interposable and available_externally linkages");
+#endif
+ }
for (auto &S : VI.getSummaryList())
S->setLive(true);