From dba1b32ded75994d99d9ecaf30447da8977017fe Mon Sep 17 00:00:00 2001
From: George Rimar <grimar@accesssoftek.com>
Date: Fri, 2 Feb 2018 12:17:33 +0000
Subject: [PATCH] [ThinLTO] - Fix for "ThinLTO inlines variables that should be
 discarded".

This fixes PR36187.

Patch teaches ThinLTO to drop non-prevailing variables,
just like we recently did for functions (in r323633).

Differential revision: https://reviews.llvm.org/D42798

llvm-svn: 324075
---
 lib/LTO/LTOBackend.cpp                        | 18 ++++++----
 .../X86/not-prevailing-variables.ll           | 35 +++++++++++++++++++
 test/tools/gold/X86/global_with_section.ll    |  4 ++-
 3 files changed, 50 insertions(+), 7 deletions(-)
 create mode 100644 test/LTO/Resolution/X86/not-prevailing-variables.ll

diff --git a/lib/LTO/LTOBackend.cpp b/lib/LTO/LTOBackend.cpp
index 1898d4bb25c..4595ea84b1e 100644
--- a/lib/LTO/LTOBackend.cpp
+++ b/lib/LTO/LTOBackend.cpp
@@ -401,13 +401,19 @@ Error lto::backend(Config &C, AddStreamFn AddStream,
 
 static void dropDeadSymbols(Module &Mod, const GVSummaryMapTy &DefinedGlobals,
                             const ModuleSummaryIndex &Index) {
-  for (auto &GV : Mod) {
+  auto MaybeDrop = [&](GlobalValue &GV) {
     auto It = DefinedGlobals.find(GV.getGUID());
-    if (It == DefinedGlobals.end())
-      continue;
-    if (!Index.isGlobalValueLive(It->second))
-      convertToDeclaration(GV);
-  }
+    if (It != DefinedGlobals.end())
+      if (!Index.isGlobalValueLive(It->second))
+        convertToDeclaration(GV);
+  };
+
+  // Process functions and global now.
+  // FIXME: add support for aliases (needs support in convertToDeclaration).
+  for (auto &GV : Mod)
+    MaybeDrop(GV);
+  for (auto &GV : Mod.globals())
+    MaybeDrop(GV);
 }
 
 Error lto::thinBackend(Config &Conf, unsigned Task, AddStreamFn AddStream,
diff --git a/test/LTO/Resolution/X86/not-prevailing-variables.ll b/test/LTO/Resolution/X86/not-prevailing-variables.ll
new file mode 100644
index 00000000000..2b6073ab154
--- /dev/null
+++ b/test/LTO/Resolution/X86/not-prevailing-variables.ll
@@ -0,0 +1,35 @@
+; RUN: opt -module-summary %s -o %t1.o
+; RUN: llvm-lto2 run -save-temps -o %t2.o %t1.o      \
+; RUN:   -r %t1.o,testVar1,plx -r %t1.o,testVar2,plx \
+; RUN:   -r %t1.o,var1,pl -r %t1.o,var2,lx
+
+; Test contains two variables: var1 and var2.
+; var2 is not prevailing and here we check it is not inlined.
+
+; Check 'var2' was not inlined.
+; RUN: llvm-objdump -d %t2.o.1 | FileCheck %s
+; CHECK:      testVar1:
+; CHECK-NEXT:   movl $10, %eax
+; CHECK-NEXT:   retq
+; CHECK:      testVar2:
+; CHECK-NEXT:   movl  (%rip), %eax
+; CHECK-NEXT:   retq
+
+; Check 'var2' is undefined.
+; RUN: llvm-readelf --symbols %t2.o.1 | FileCheck %s --check-prefix=UND
+; UND: NOTYPE  GLOBAL DEFAULT UND var2
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+@var1 = global i32 10, align 4
+define i32 @testVar1() {
+  %1 = load i32, i32* @var1, align 4
+  ret i32 %1
+}
+
+@var2 = global i32 11, align 4
+define i32 @testVar2() {
+  %1 = load i32, i32* @var2, align 4
+  ret i32 %1
+}
diff --git a/test/tools/gold/X86/global_with_section.ll b/test/tools/gold/X86/global_with_section.ll
index 4728ae34439..8ea4246c49c 100644
--- a/test/tools/gold/X86/global_with_section.ll
+++ b/test/tools/gold/X86/global_with_section.ll
@@ -45,7 +45,9 @@ target triple = "x86_64-unknown-linux-gnu"
 
 ; Confirm via a variable with a non-C identifier section that we are getting
 ; the expected internalization.
-; CHECK-DAG: @var_with_nonC_section = internal global i32 0, section ".nonCsection"
+; CHECK-REGULARLTO-DAG: @var_with_nonC_section = internal global i32 0, section ".nonCsection"
+; Check we dropped definition of dead variable.
+; CHECK-THINLTO-DAG: @var_with_nonC_section = external dso_local global i32, section ".nonCsection"
 @var_with_nonC_section = global i32 0, section ".nonCsection"
 
 ; We should not internalize @deadfunc_with_section due to section