[LTO] Drop non-prevailing definitions only if linkage is not local or appending

Summary:
This fixes PR 37422

In ELF, non-weak symbols can also be non-prevailing.  In this particular
PR, the __llvm_profile_* symbols are non-prevailing but weren't getting
dropped - causing multiply-defined errors with lld.

Also add a test, strong_non_prevailing.ll, to ensure that multiple
copies of a strong symbol are dropped.

To fix the test regressions exposed by this fix,
- do not mark prevailing copies for symbols with 'appending' linkage.
There's no one prevailing copy for such symbols.
- fix the prevailing version in dead-strip-fulllto.ll
- explicitly pass exported symbols to llvm-lto in fumcimport.ll and
funcimport_var.ll

Reviewers: tejohnson, pcc

Subscribers: mehdi_amini, inglorion, eraman, steven_wu, dexonsmith,
dang, srhines, llvm-commits

Differential Revision: https://reviews.llvm.org/D54125

llvm-svn: 346436

1 files changed, 1 insertions, 1 deletions

diff --git a/llvm/test/Transforms/FunctionImport/funcimport_var.ll b/llvm/test/Transforms/FunctionImport/funcimport_var.ll
index a93cabba69a..edd874e6297 100644
--- a/llvm/test/Transforms/FunctionImport/funcimport_var.ll
+++ b/llvm/test/Transforms/FunctionImport/funcimport_var.ll
@@ -4,7 +4,7 @@
 ; RUN: opt -module-summary %p/Inputs/funcimport_var2.ll -o %t2.bc
 ; RUN: llvm-lto -thinlto -thinlto-action=thinlink -o %t3 %t.bc %t2.bc
 ; RUN: llvm-lto -thinlto -thinlto-action=import -thinlto-index=%t3 %t.bc %t2.bc
-; RUN: llvm-lto -thinlto -thinlto-action=run %t.bc %t2.bc
+; RUN: llvm-lto -thinlto -thinlto-action=run %t.bc %t2.bc -exported-symbol=_Z4LinkPKcS0_
 ; RUN: llvm-nm %t.bc.thinlto.o | FileCheck %s
 ; RUN: llvm-lto2 run %t.bc %t2.bc -o %t.out \
 ; RUN:   -r %t.bc,_Z4LinkPKcS0_,plx \