[ThinLTO] Convert dead alias to declarations

Summary:
This complements the fixes in r323633 and r324075 which drop the
definitions of dead functions and variables, respectively.

Fixes PR36208.

Reviewers: grimar, rafael

Subscribers: mehdi_amini, llvm-commits, inglorion

Differential Revision: https://reviews.llvm.org/D42856

llvm-svn: 324242

1 files changed, 43 insertions, 0 deletions

diff --git a/llvm/test/LTO/Resolution/X86/not-prevailing-alias.ll b/llvm/test/LTO/Resolution/X86/not-prevailing-alias.ll
new file mode 100644
index 00000000000..79770c5cf4c
--- /dev/null
+++ b/llvm/test/LTO/Resolution/X86/not-prevailing-alias.ll
@@ -0,0 +1,43 @@
+; Test to ensure that dead alias are dropped by converting to a declaration
+; RUN: opt -module-summary %s -o %t1.bc
+; RUN: llvm-lto2 run %t1.bc -r %t1.bc,barAlias,x \
+; RUN:   -r %t1.bc,bar,x -r %t1.bc,zed,px \
+; RUN:   -r %t1.bc,var,x -r %t1.bc,varAlias,x \
+; RUN:   -o %t2.o -save-temps
+
+; Check that bar and barAlias were dropped to declarations
+; RUN: llvm-dis %t2.o.1.1.promote.bc -o - | FileCheck %s --check-prefix=DROP
+; DROP-DAG: declare void @bar()
+; DROP-DAG: declare void @barAlias()
+; DROP-DAG: @var = external global i32
+; DROP-DAG: @varAlias = external global i32
+
+; Check that 'barAlias' and 'varAlias' were not inlined.
+; RUN: llvm-objdump -d %t2.o.1 | FileCheck %s
+; CHECK:      zed:
+; CHECK-NEXT:  {{.*}}  pushq
+; CHECK-NEXT:  {{.*}}  callq   0
+; CHECK-NEXT:   movq  (%rip), %rax
+
+; Check that 'barAlias' and 'varAlias' produced as undefined.
+; RUN: llvm-readelf --symbols %t2.o.1 | FileCheck %s --check-prefix=SYMBOLS
+; SYMBOLS: NOTYPE  GLOBAL DEFAULT  UND barAlias
+; SYMBOLS: NOTYPE  GLOBAL DEFAULT  UND varAlias
+; SYMBOLS: FUNC    GLOBAL DEFAULT    2 zed
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+@barAlias = alias void(), void()* @bar
+define void @bar() {
+  ret void
+}
+
+@var = global i32 99
+@varAlias = alias i32, i32* @var
+
+define i32 @zed() {
+  call void @barAlias()
+  %1 = load i32, i32* @varAlias, align 4
+  ret i32 %1
+}