[ThinLTO] Scan all variants of vague symbol for reachability.

Summary:
Alias can make one (but not all) live, we still need to scan all others if this symbol is reachable
from somewhere else.

Reviewers: tejohnson, grimar

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

Differential Revision: https://reviews.llvm.org/D56117

llvm-svn: 350269

llvm/lib/Transforms/IPO/FunctionImport.cpp

@@ -777,9 +777,14 @@ void llvm::computeDeadSymbols(
     VI = updateValueInfoForIndirectCalls(Index, VI);
     if (!VI)
       return;
-    for (auto &S : VI.getSummaryList())
-      if (S->isLive())
-        return;
+
+    // We need to make sure all variants of the symbol are scanned, alias can
+    // make one (but not all) alive.
+    if (llvm::all_of(VI.getSummaryList(),
+                     [](const std::unique_ptr<llvm::GlobalValueSummary> &S) {
+                       return S->isLive();
+                     }))
+      return;
 
     // We only keep live symbols that are known to be non-prevailing if any are
     // available_externally, linkonceodr, weakodr. Those symbols are discarded

llvm/test/ThinLTO/X86/Inputs/deadstrip.ll

@@ -20,3 +20,8 @@ define void @another_dead_func() {
     call void @dead_func()
     ret void
 }
+
+define linkonce_odr void @linkonceodrfuncwithalias() {
+entry:
+  ret void
+}

llvm/test/ThinLTO/X86/deadstrip.ll

@@ -20,10 +20,14 @@
 ; RUN:   -r %t1.bc,_live_available_externally_func,l \
 ; RUN:   -r %t1.bc,_live_linkonce_odr_func,l \
 ; RUN:   -r %t1.bc,_live_weak_odr_func,l \
+; RUN:   -r %t1.bc,_linkonceodralias,pl \
+; RUN:   -r %t1.bc,_linkonceodrfuncwithalias,l \
+; RUN:   -r %t1.bc,_linkonceodrfuncwithalias_caller,pl \
 ; RUN:   -r %t2.bc,_baz,pl \
 ; RUN:   -r %t2.bc,_boo,pl \
 ; RUN:   -r %t2.bc,_dead_func,l \
 ; RUN:   -r %t2.bc,_another_dead_func,pl \
+; RUN:   -r %t2.bc,_linkonceodrfuncwithalias,pl \
 ; RUN:   -thinlto-threads=1 \
 ; RUN:	 -debug-only=function-import 2>&1 | FileCheck %s --check-prefix=DEBUG --check-prefix=STATS
 ; RUN: llvm-dis < %t.out.1.3.import.bc | FileCheck %s --check-prefix=LTO2
@@ -71,6 +75,11 @@
 ; llvm.global_ctors
 ; CHECK2: define void @boo()
 ; LTO2-CHECK2: define dso_local void @boo()
+
+; Make sure we keep @linkonceodrfuncwithalias in Input/deadstrip.ll alive as it
+; is reachable from @main.
+; LTO2-CHECK2: define weak_odr dso_local void @linkonceodrfuncwithalias() {
+
 ; We should have eventually removed @baz since it was internalized and unused
 ; CHECK2-NM-NOT: _baz
 
@@ -105,10 +114,14 @@
 ; RUN:   -r %t1.bc,_live_available_externally_func,l \
 ; RUN:   -r %t1.bc,_live_linkonce_odr_func,l \
 ; RUN:   -r %t1.bc,_live_weak_odr_func,l \
+; RUN:   -r %t1.bc,_linkonceodralias,pl \
+; RUN:   -r %t1.bc,_linkonceodrfuncwithalias,l \
+; RUN:   -r %t1.bc,_linkonceodrfuncwithalias_caller,pl \
 ; RUN:   -r %t3.bc,_baz,pl \
 ; RUN:   -r %t3.bc,_boo,pl \
 ; RUN:   -r %t3.bc,_dead_func,l \
-; RUN:   -r %t3.bc,_another_dead_func,pl
+; RUN:   -r %t3.bc,_another_dead_func,pl \
+; RUN:   -r %t3.bc,_linkonceodrfuncwithalias,pl
 ; RUN: llvm-dis < %t4.out.1.3.import.bc | FileCheck %s --check-prefix=CHECK-NOTDEAD
 ; RUN: llvm-nm %t4.out.0 | FileCheck %s --check-prefix=CHECK-NM-NOTDEAD
 
@@ -163,11 +176,31 @@ define available_externally void @live_available_externally_func() {
     ret void
 }
 
+; This alias will set its base object in this file (linkonceodrfuncwithalias)
+; alive.
+; We want to make sure the @linkonceodrfuncwithalias copy in Input/deadstrip.ll
+; is also scanned when computing reachability.
+@linkonceodralias = linkonce_odr alias void (), void ()* @linkonceodrfuncwithalias
+
+define linkonce_odr void @linkonceodrfuncwithalias() {
+entry:
+  ret void
+}
+
+define void @linkonceodrfuncwithalias_caller() {
+entry:
+  call void @linkonceodrfuncwithalias()
+  ret void
+}
+
+
 define void @main() {
     call void @bar()
     call void @bar_internal()
     call void @live_linkonce_odr_func()
     call void @live_weak_odr_func()
     call void @live_available_externally_func()
+    call void @linkonceodrfuncwithalias_caller()
+    call void @linkonceodralias()
     ret void
 }