[lld] r314097 - [ELF] - LTO: do not optimize away symbols accessed from linkerscript.
George Rimar via llvm-commits
llvm-commits at lists.llvm.org
Mon Sep 25 02:31:44 PDT 2017
Author: grimar
Date: Mon Sep 25 02:31:43 2017
New Revision: 314097
URL: http://llvm.org/viewvc/llvm-project?rev=314097&view=rev
Log:
[ELF] - LTO: do not optimize away symbols accessed from linkerscript.
Previously when BC file had global variable that was accessed from script,
it was optimized away or inlined by IPO.
In this patch I add symbols at left side of assignment expression as LinkerRedefined,
what prevents optimization for them.
Differential revision: https://reviews.llvm.org/D37059
Added:
lld/trunk/test/ELF/lto/Inputs/linker-script-symbols-ipo.ll
lld/trunk/test/ELF/lto/linker-script-symbols-assign.ll
lld/trunk/test/ELF/lto/linker-script-symbols-ipo.ll
Modified:
lld/trunk/ELF/LTO.cpp
Modified: lld/trunk/ELF/LTO.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/LTO.cpp?rev=314097&r1=314096&r2=314097&view=diff
==============================================================================
--- lld/trunk/ELF/LTO.cpp (original)
+++ lld/trunk/ELF/LTO.cpp Mon Sep 25 02:31:43 2017
@@ -10,6 +10,7 @@
#include "LTO.h"
#include "Config.h"
#include "Error.h"
+#include "LinkerScript.h"
#include "InputFiles.h"
#include "SymbolTable.h"
#include "Symbols.h"
@@ -128,6 +129,11 @@ void BitcodeCompiler::add(BitcodeFile &F
std::vector<SymbolBody *> Syms = F.getSymbols();
std::vector<lto::SymbolResolution> Resols(Syms.size());
+ DenseSet<StringRef> ScriptSymbols;
+ for (BaseCommand *Base : Script->Opt.Commands)
+ if (auto *Cmd = dyn_cast<SymbolAssignment>(Base))
+ ScriptSymbols.insert(Cmd->Name);
+
// Provide a resolution to the LTO API for each symbol.
for (const lto::InputFile::Symbol &ObjSym : Obj.symbols()) {
SymbolBody *B = Syms[SymNum];
@@ -153,7 +159,13 @@ void BitcodeCompiler::add(BitcodeFile &F
UsedStartStop.count(ObjSym.getSectionName());
if (R.Prevailing)
undefine(Sym);
- R.LinkerRedefined = !Sym->CanInline;
+
+ // We tell LTO to not apply interprocedural optimization for following
+ // symbols because otherwise LTO would inline them while their values are
+ // still not final:
+ // 1) Aliased (with --defsym) or wrapped (with --wrap) symbols.
+ // 2) Symbols redefined in linker script.
+ R.LinkerRedefined = !Sym->CanInline || ScriptSymbols.count(B->getName());
}
checkError(LTOObj->add(std::move(F.Obj), Resols));
}
Added: lld/trunk/test/ELF/lto/Inputs/linker-script-symbols-ipo.ll
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/lto/Inputs/linker-script-symbols-ipo.ll?rev=314097&view=auto
==============================================================================
--- lld/trunk/test/ELF/lto/Inputs/linker-script-symbols-ipo.ll (added)
+++ lld/trunk/test/ELF/lto/Inputs/linker-script-symbols-ipo.ll Mon Sep 25 02:31:43 2017
@@ -0,0 +1,9 @@
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+declare i32 @bar()
+
+define i32 @_start() {
+ %1 = tail call i32 @bar()
+ ret i32 %1
+}
Added: lld/trunk/test/ELF/lto/linker-script-symbols-assign.ll
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/lto/linker-script-symbols-assign.ll?rev=314097&view=auto
==============================================================================
--- lld/trunk/test/ELF/lto/linker-script-symbols-assign.ll (added)
+++ lld/trunk/test/ELF/lto/linker-script-symbols-assign.ll Mon Sep 25 02:31:43 2017
@@ -0,0 +1,50 @@
+; REQUIRES: x86
+; RUN: llvm-as %s -o %t.o
+
+; RUN: echo "foo = 1;" > %t.script
+; RUN: ld.lld -m elf_x86_64 %t.o -o %t2 --script %t.script -save-temps
+; RUN: llvm-readobj -symbols %t2.lto.o | FileCheck %s
+
+; CHECK-NOT: bar
+; CHECK: Symbol {
+; CHECK: Name: foo
+; CHECK-NEXT: Value: 0x0
+; CHECK-NEXT: Size: 4
+; FIXME: Binding should be Global here. Symbols redefined in script does not
+; receive correct binding and visibility, this is a known bug.
+; CHECK-NEXT: Binding: Weak
+; CHECK-NEXT: Type: Object
+; CHECK-NEXT: Other: 0
+; CHECK-NEXT: Section: .bss.foo
+; CHECK-NEXT: }
+; CHECK-NEXT:]
+
+; RUN: llvm-readobj -symbols %t2 | FileCheck %s --check-prefix=VAL
+; VAL: Symbol {
+; VAL: Name: foo
+; VAL-NEXT: Value: 0x1
+; VAL-NEXT: Size:
+; VAL-NEXT: Binding: Global
+; VAL-NEXT: Type: None
+; VAL-NEXT: Other:
+; VAL-NEXT: Section: Absolute
+; VAL-NEXT: }
+
+; RUN: echo "zed = 1;" > %t2.script
+; RUN: ld.lld -m elf_x86_64 %t.o -o %t3 --script %t2.script
+; RUN: llvm-readobj -symbols %t3 | FileCheck %s --check-prefix=ABS
+; ABS: Symbol {
+; ABS: Name: zed
+; ABS-NEXT: Value: 0x1
+; ABS-NEXT: Size: 0
+; ABS-NEXT: Binding: Global
+; ABS-NEXT: Type: None
+; ABS-NEXT: Other: 0
+; ABS-NEXT: Section: Absolute
+; ABS-NEXT: }
+
+target triple = "x86_64-unknown-linux-gnu"
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+
+ at foo = global i32 0
+ at bar = global i32 0
Added: lld/trunk/test/ELF/lto/linker-script-symbols-ipo.ll
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/lto/linker-script-symbols-ipo.ll?rev=314097&view=auto
==============================================================================
--- lld/trunk/test/ELF/lto/linker-script-symbols-ipo.ll (added)
+++ lld/trunk/test/ELF/lto/linker-script-symbols-ipo.ll Mon Sep 25 02:31:43 2017
@@ -0,0 +1,32 @@
+; REQUIRES: x86
+; RUN: llvm-as %s -o %t1.o
+; RUN: llvm-as %S/Inputs/linker-script-symbols-ipo.ll -o %t2.o
+; RUN: echo "bar = foo;" > %t.script
+
+;; Check that without linkerscript bar is inlined.
+; RUN: ld.lld -m elf_x86_64 %t1.o %t2.o -o %t3 -save-temps
+; RUN: llvm-objdump -d %t3 | FileCheck %s --check-prefix=IPO
+; IPO: Disassembly of section .text:
+; IPO: _start:
+; IPO-NEXT: 201000: {{.*}} movl $1, %eax
+; IPO-NEXT: 201005: {{.*}} retq
+
+;; Check that LTO does not do IPO for symbols assigned by script.
+; RUN: ld.lld -m elf_x86_64 %t1.o %t2.o -o %t4 --script %t.script -save-temps
+; RUN: llvm-objdump -d %t4 | FileCheck %s --check-prefix=NOIPO
+; NOIPO: Disassembly of section .text:
+; NOIPO: foo:
+; NOIPO-NEXT: 201010: {{.*}} movl $2, %eax
+; NOIPO: _start:
+; NOIPO-NEXT: 201020: {{.*}} jmp -21 <foo>
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define i32 @bar() {
+ ret i32 1
+}
+
+define i32 @foo() {
+ ret i32 2
+}
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