[lld] Add --lto-debug-pass-manager option

[ellis]

Summary

Add support for printing the passes run for LTO.

Both ELF and COFF have --lto-debug-pass-manager (-ltodebugpassmanager) to print the compiler passes run during LTO. This is useful to check that a certain compiler pass is run in a test, e.g., https://reviews.llvm.org/D151589

[MaskRay]

lto-pass-manager may be a better name.

[int3]

lto-pass-manager may be a better name.

but (as I understand) this is about *debugging* the pass manager...

[ellis]

In D151746#4382320, @MaskRay wrote:

lto-pass-manager may be a better name.

Also, I think it makes sense to stay consistent with ELF which uses --lto-debug-pass-manager

[ellis]

Rename test function to foo since _start is not a necessary symbol

[ellis]

I've landed this while keeping the flag consistent with ELF, but I'm happy to make changes if needed.

lld/MachO/Config.h

struct Configuration {
   llvm::SmallVector<llvm::StringRef, 0> runtimePaths;
   std::vector<std::string> astPaths;
   std::vector<Symbol *> explicitUndefineds;
   llvm::StringSet<> explicitDynamicLookups;
   // There are typically few custom sectionAlignments or segmentProtections,
   // so use a vector instead of a map.
   std::vector<SectionAlign> sectionAlignments;
   std::vector<SegmentProtection> segmentProtections;
+  bool ltoDebugPassManager = false;
 
   bool callGraphProfileSort = false;
   llvm::StringRef printSymbolOrder;
 
   SectionRenameMap sectionRenameMap;
   SegmentRenameMap segmentRenameMap;
 
   bool hasExplicitExports = false;

lld/MachO/Driver.cpp

bool macho::link(ArrayRef<const char *> argsArr, llvm::raw_ostream &stdoutOS,
   config->printSymbolOrder = args.getLastArgValue(OPT_print_symbol_order_eq);
   config->forceExactCpuSubtypeMatch =
       getenv("LD_DYLIB_CPU_SUBTYPES_MUST_MATCH");
   config->objcStubsMode = getObjCStubsMode(args);
   config->ignoreAutoLink = args.hasArg(OPT_ignore_auto_link);
   for (const Arg *arg : args.filtered(OPT_ignore_auto_link_option))
     config->ignoreAutoLinkOptions.insert(arg->getValue());
   config->strictAutoLink = args.hasArg(OPT_strict_auto_link);
+  config->ltoDebugPassManager = args.hasArg(OPT_lto_debug_pass_manager);
 
   for (const Arg *arg : args.filtered(OPT_alias)) {
     config->aliasedSymbols.push_back(
         std::make_pair(arg->getValue(0), arg->getValue(1)));
   }
 
   if (const char *zero = getenv("ZERO_AR_DATE"))
     config->zeroModTime = strcmp(zero, "0") != 0;

lld/MachO/LTO.cpp

static lto::Config createConfig() {
   c.PreCodeGenPassesHook = [](legacy::PassManager &pm) {
     pm.add(createObjCARCContractPass());
   };
 
   c.AlwaysEmitRegularLTOObj = !config->ltoObjPath.empty();
 
   c.TimeTraceEnabled = config->timeTraceEnabled;
   c.TimeTraceGranularity = config->timeTraceGranularity;
+  c.DebugPassManager = config->ltoDebugPassManager;
   c.OptLevel = config->ltoo;
   c.CGOptLevel = config->ltoCgo;
   if (config->saveTemps)
     checkError(c.addSaveTemps(config->outputFile.str() + ".",
                               /*UseInputModulePath=*/true));
   return c;
 }
 

lld/MachO/Options.td

def ignore_auto_link_option_eq : Joined<["--"], "ignore-auto-link-option=">,
     HelpText<"Ignore a single auto-linked library or framework. Useful to ignore invalid options that ld64 ignores">,
     Group<grp_lld>;
 def strict_auto_link : Flag<["--"], "strict-auto-link">,
     HelpText<"Always warn for missing frameworks or libraries if they are loaded via LC_LINKER_OPTIONS">,
     Group<grp_lld>;
 def check_category_conflicts : Flag<["--"], "check-category-conflicts">,
     HelpText<"Check for conflicts between category & class methods">,
     Group<grp_lld>;
+def lto_debug_pass_manager: Flag<["--"], "lto-debug-pass-manager">,
+    HelpText<"Debug new pass manager">, Group<grp_lld>;
 
 // This is a complete Options.td compiled from Apple's ld(1) manpage
 // dated 2018-03-07 and cross checked with ld64 source code in repo
 // https://github.com/apple-opensource/ld64 at git tag "512.4" dated
 // 2018-03-18.
 
 // Flags<[HelpHidden]> marks options that are not yet ported to lld,
 // and serve as a scoreboard for annotating our progress toward

lld/test/MachO/new-pass-manager.ll

+; REQUIRES: x86
+
+; RUN: llvm-as %s -o %t.o
+; RUN: %lld -dylib --lto-debug-pass-manager -o /dev/null %t.o 2>&1 | FileCheck %s
+
+; CHECK: Running pass: GlobalOptPass
+
+target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-darwin"
+
+define void @foo() {
+entry:
+  ret void
+}