[ELF] Allow --reproduce to be specified as an env variable

[davide]

Summary

For context:
https://llvm.org/bugs/show_bug.cgi?id=28257

[davide]

Example repro (just used to reproduce a libreoffice link failure)

$ export LLD_REPRODUCE=patatino
$ echo $LLD_REPRODUCE
patatino
$ make
mkdir -p /home/davide/lto_experiments/libreoffice/instdir
/home/davide/lto_experiments/libreoffice/solenv/bin/install-gdb-printers -a /home/davide/lto_experiments/libreoffice/instdir -c
make -j 1  -rs -f /home/davide/lto_experiments/libreoffice/Makefile.gbuild    all
[build DEP] LNK:Library/libsal_textenclo.so
[build LNK] Library/libsal_textenclo.so
undefined symbol: _ZN3sal6detail7textenc37handleBadInputTextToUnicodeConversionEbbcjPPDsS2_Pj in /home/davide/lto_experiments/libreoffice/workdir/CxxObject/sal/textenc/convertbig5hkscs.o
undefined symbol: _ZN3sal6detail7textenc37handleBadInputUnicodeToTextConversionEbjjPPcS2_PjPKcmPb in /home/davide/lto_experiments/libreoffice/workdir/CxxObject/sal/textenc/convertbig5hkscs.o
undefined symbol: _ZN3sal6detail7textenc20convertCharToUnicodeEPKvPvPKcmPDsmjPjPm in /home/davide/lto_experiments/libreoffice/workdir/CxxObject/sal/textenc/tables.o
undefined symbol: _ZN3sal6detail7textenc20convertUnicodeToCharEPKvPvPKDsmPcmjPjPm in /home/davide/lto_experiments/libreoffice/workdir/CxxObject/sal/textenc/tables.o
undefined symbol: _ZN3sal6detail7textenc32handleUndefinedUnicodeToTextCharEPPKDsS3_PPcPKcjPj in /home/davide/lto_experiments/libreoffice/workdir/CxxObject/sal/textenc/tcvtbyte.o
clang-3.9: error: linker command failed with exit code 1 (use -v to see invocation)
/home/davide/lto_experiments/libreoffice/sal/Library_sal_textenc.mk:11: recipe for target '/home/davide/lto_experiments/libreoffice/instdir/program/libsal_textenclo.so' failed
make[1]: *** [/home/davide/lto_experiments/libreoffice/instdir/program/libsal_textenclo.so] Error 1
Makefile:254: recipe for target 'build' failed
make: *** [build] Error 2

$ find . -name "patatino*"
./patatino.cpio

[ruiu]

ELF/Driver.cpp

257–261

Please separate this code as getReproduceOption function and then use it as

if (const char *Path = getReproduceOption()) {
  ...
}

Do you need :: for getenv?

[davide]

Addressed Rui's comments.

[ruiu]

LGTM with a few nits.[[ URL | name ]]

ELF/Driver.cpp

239

This variable is dead.

257–262

This line has two occurrence of Reproduce. This is too much. I'd name just Path.

ELF/Driver.cpp

 #include "SymbolTable.h"
 #include "Target.h"
 #include "Writer.h"
 #include "lld/Driver/Driver.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/StringSwitch.h"
 #include "llvm/Support/TargetSelect.h"
 #include "llvm/Support/raw_ostream.h"
+#include <cstdlib>
 #include <utility>
 
 using namespace llvm;
 using namespace llvm::ELF;
 using namespace llvm::object;
 using namespace llvm::sys;
 
 using namespace lld;
if (auto *Arg = Args.getLastArg(Key)) {
     StringRef S = Arg->getValue();
     if (S.getAsInteger(10, V))
       error(Arg->getSpelling() + ": number expected, but got " + S);
   }
   return V;
 }
 
 static bool hasZOption(opt::InputArgList &Args, StringRef Key) {
   for (auto *Arg : Args.filtered(OPT_z))
     if (Key == Arg->getValue())
       return true;
   return false;
 }
 
 void LinkerDriver::main(ArrayRef<const char *> ArgsArr) {
   ELFOptTable Parser;
   opt::InputArgList Args = Parser.parse(ArgsArr.slice(1));
   if (Args.hasArg(OPT_help)) {
     printHelp(ArgsArr[0]);
     return;
   }
   if (Args.hasArg(OPT_version)) {
     outs() << getVersionString();
     return;
   }
 
-  if (auto *Arg = Args.getLastArg(OPT_reproduce)) {
+  const char *ReproducePath = nullptr;
+  if (Args.hasArg(OPT_reproduce))
+    ReproducePath = Args.getLastArg(OPT_reproduce)->getValue();
+  else
+    ReproducePath = ::getenv("LLD_REPRODUCE");
+  if (ReproducePath) {
     // Note that --reproduce is a debug option so you can ignore it
     // if you are trying to understand the whole picture of the code.
-    Cpio.reset(CpioFile::create(Arg->getValue()));
+    Cpio.reset(CpioFile::create(ReproducePath));
     if (Cpio) {
       Cpio->append("response.txt", createResponseFile(Args));
       Cpio->append("version.txt", getVersionString());
     }
   }
 
   readConfigs(Args);
   initLLVM(Args);

test/ELF/reproduce.s

 # RSP-NEXT: --as-needed
 
 # RUN: FileCheck %s --check-prefix=VERSION < repro/version.txt
 # VERSION: LLD
 
 # RUN: mkdir -p %t.dir/build2/a/b/c
 # RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.dir/build2/foo.o
 # RUN: cd %t.dir/build2/a/b/c
-# RUN: ld.lld ./../../../foo.o -o bar -shared --as-needed --reproduce repro
+# RUN: env LLD_REPRODUCE=repro ld.lld ./../../../foo.o -o bar -shared --as-needed
 # RUN: cpio -id < repro.cpio
 # RUN: diff %t.dir/build2/foo.o repro/%:t.dir/build2/foo.o
 
 # RUN: echo "{ local: *; };" >  ver
 # RUN: echo > dyn
 # RUN: echo > file
 # RUN: echo > file2
 # RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o 'foo bar'