ELF: Add cache pruning support.

[pcc]

Summary

This patch causes us to use pruneCache() to prune the ThinLTO cache after
completing LTO. A new flag --thinlto-cache-policy allows users to configure
the policy.

Depends on D31020

[mehdi_amini]

lld/ELF/LTO.cpp

167

Not interested in adding a CachePolicy on the config and having this at the end of the LTO process?

[pcc]

lld/ELF/LTO.cpp

167

I thought about doing something like that, but I couldn't see a clean way to do it, as the LTO implementation is supposed to be independent of the type of cache being used.

[mehdi_amini]

lld/ELF/LTO.cpp

167

Fair!

[pcc]

@ruiu Ping.

[ruiu]

LGTM

lld/ELF/Config.h

165

Should be moved to line 76.

lld/ELF/Driver.cpp

590

"-thinlto-cache-policy: invalid cache policy"

lld/ELF/Config.h

 //===- Config.h -------------------------------------------------*- C++ -*-===//
 //
 //                             The LLVM Linker
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLD_ELF_CONFIG_H
 #define LLD_ELF_CONFIG_H
 
 #include "llvm/ADT/MapVector.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/StringSet.h"
+#include "llvm/Support/CachePruning.h"
 #include "llvm/Support/CodeGen.h"
 #include "llvm/Support/ELF.h"
 
 #include <vector>
 
 namespace lld {
 namespace elf {
 
struct Configuration {
   uint64_t ErrorLimit = 20;
   uint64_t ImageBase;
   uint64_t MaxPageSize;
   uint64_t ZStackSize;
   unsigned LTOPartitions;
   unsigned LTOO;
   unsigned Optimize;
   unsigned ThinLTOJobs;
+  llvm::CachePruningPolicy ThinLTOCachePolicy;
 
   // Returns true if target is 64 bit.
   bool is64Bit() const { return EKind == ELF64LEKind || EKind == ELF64BEKind; }
 
   // The ELF spec defines two types of relocation table entries, RELA and
   // REL. RELA is a triplet of (offset, info, addend) while REL is a
   // tuple of (offset, info). Addends for REL are implicit and read from
   // the location where the relocations are applied. So, REL is more

lld/ELF/Driver.cpp

void LinkerDriver::readConfigs(opt::InputArgList &Args) {
   Config->SingleRoRx = Args.hasArg(OPT_no_rosegment);
   Config->SoName = getString(Args, OPT_soname);
   Config->SortSection = getSortSection(Args);
   Config->Strip = getStrip(Args);
   Config->Sysroot = getString(Args, OPT_sysroot);
   Config->Target1Rel = getArg(Args, OPT_target1_rel, OPT_target1_abs, false);
   Config->Target2 = getTarget2(Args);
   Config->ThinLTOCacheDir = getString(Args, OPT_thinlto_cache_dir);
+  Config->ThinLTOCachePolicy =
+      check(parseCachePruningPolicy(getString(Args, OPT_thinlto_cache_policy)),
+            "invalid cache policy");
   Config->ThinLTOJobs = getInteger(Args, OPT_thinlto_jobs, -1u);
   Config->Threads = getArg(Args, OPT_threads, OPT_no_threads, true);
   Config->Trace = Args.hasArg(OPT_trace);
   Config->Undefined = getArgs(Args, OPT_undefined);
   Config->UnresolvedSymbols = getUnresolvedSymbolPolicy(Args);
   Config->Verbose = Args.hasArg(OPT_verbose);
   Config->WarnCommon = Args.hasArg(OPT_warn_common);
   Config->ZCombreloc = !hasZOption(Args, "nocombreloc");

lld/ELF/LTO.cpp

std::vector<InputFile *> BitcodeCompiler::compile() {
 
   checkError(LTOObj->run(
       [&](size_t Task) {
         return llvm::make_unique<lto::NativeObjectStream>(
             llvm::make_unique<raw_svector_ostream>(Buff[Task]));
       },
       Cache));
 
+  if (!Config->ThinLTOCacheDir.empty())
+    pruneCache(Config->ThinLTOCacheDir, Config->ThinLTOCachePolicy);
+
   for (unsigned I = 0; I != MaxTasks; ++I) {
     if (Buff[I].empty())
       continue;
     if (Config->SaveTemps) {
       if (I == 0)
         saveBuffer(Buff[I], Config->OutputFile + ".lto.o");
       else
         saveBuffer(Buff[I], Config->OutputFile + Twine(I) + ".lto.o");

lld/ELF/Options.td

 def mllvm: S<"mllvm">;
 def opt_remarks_filename: Separate<["--"], "opt-remarks-filename">,
   HelpText<"YAML output file for optimization remarks">;
 def opt_remarks_with_hotness: Flag<["--"], "opt-remarks-with-hotness">,
   HelpText<"Include hotness informations in the optimization remarks file">;
 def save_temps: F<"save-temps">;
 def thinlto_cache_dir: J<"thinlto-cache-dir=">,
   HelpText<"Path to ThinLTO cached object file directory">;
+def thinlto_cache_policy: S<"thinlto-cache-policy">,
+  HelpText<"Pruning policy for the ThinLTO cache">;
 def thinlto_jobs: J<"thinlto-jobs=">, HelpText<"Number of ThinLTO jobs">;

lld/test/ELF/lto/cache.ll

 ; REQUIRES: x86
 
 ; RUN: opt -module-hash -module-summary %s -o %t.o
 ; RUN: opt -module-hash -module-summary %p/Inputs/cache.ll -o %t2.o
 
-; RUN: rm -Rf %t.cache
-; RUN: ld.lld --thinlto-cache-dir=%t.cache -o %t3 %t2.o %t.o
+; RUN: rm -Rf %t.cache && mkdir %t.cache
+; Create a file that will be removed by cache pruning due to age.
+; RUN: touch -d 1970-01-01 %t.cache/foo
+; RUN: ld.lld --thinlto-cache-dir=%t.cache --thinlto-cache-policy prune_after=1h -o %t3 %t2.o %t.o
 
-; RUN: ls %t.cache | count 2
+; Two cached objects, plus a timestamp file, minus the file we removed.
+; RUN: ls %t.cache | count 3
 
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
 
 define void @globalfunc() #0 {
 entry:
   ret void
 }