[LTO] Make sure symbol ordering is honoured.

We do this emitting a section for every function when LTO is used.
Fixes PR33888.

Differential Revision:  https://reviews.llvm.org/D35809

llvm-svn: 308915

lld/ELF/LTO.cpp

@@ -73,6 +73,9 @@ static std::unique_ptr<lto::LTO> createLTO() {
   Conf.Options = InitTargetOptionsFromCodeGenFlags();
   Conf.Options.RelaxELFRelocations = true;
 
+  // Always emit a section per function with LTO.
+  Conf.Options.FunctionSections = true;
+
   if (Config->Relocatable)
     Conf.RelocModel = None;
   else if (Config->Pic)

lld/test/ELF/lto/Inputs/symbol-ordering-lto.ll

@@ -0,0 +1,10 @@
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-scei-ps4"
+
+define i32 @tin() {
+  ret i32 22
+}
+
+define i32 @pat() {
+  ret i32 42
+}

lld/test/ELF/lto/symbol-ordering-lto.s

@@ -0,0 +1,25 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-scei-ps4 %s -o %t.o
+# RUN: llvm-as %p/Inputs/symbol-ordering-lto.ll -o %t.bc
+
+# Set up the symbol file
+# RUN: echo "tin  " > %t_order_lto.txt
+# RUN: echo "_start " >> %t_order_lto.txt
+# RUN: echo "pat " >> %t_order_lto.txt
+
+# RUN: ld.lld --symbol-ordering-file %t_order_lto.txt %t.o %t.bc -o %t2.out
+# RUN: llvm-readobj -elf-output-style=GNU -t %t2.out| FileCheck %s
+
+# Check that the order is pat -> _start -> tin.
+
+# CHECK: Symbol table '.symtab' contains 4 entries:
+# CHECK-NEXT:   Num:    Value          Size Type    Bind   Vis      Ndx Name
+# CHECK-NEXT:     0: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT  UND
+# CHECK-NEXT:     1: 0000000000201008     0 NOTYPE  GLOBAL DEFAULT    1 _start
+# CHECK-NEXT:     2: 0000000000201020     6 FUNC    GLOBAL DEFAULT    1 pat
+# CHECK-NEXT:     3: 0000000000201000     6 FUNC    GLOBAL DEFAULT    1 tin
+
+.globl _start
+_start:
+  call pat
+  call tin