[lld-macho] Gate category checking behind --check-category-conflicts

[int3]

Summary

@oontvoo reports that the current implementation crashes on a bunch of
their builds. Let's leave it disabled by default for now.

[oontvoo]

LG Thank you!

lld/MachO/Driver.cpp

if (config->timeTraceEnabled)
 
     gatherInputSections();
     if (config->callGraphProfileSort)
       priorityBuilder.extractCallGraphProfile();
 
     if (config->deadStrip)
       markLive();
 
+    if (args.hasArg(OPT_check_category_conflicts))
       objc::checkCategories();
 
     // ICF assumes that all literals have been folded already, so we must run
     // foldIdenticalLiterals before foldIdenticalSections.
     foldIdenticalLiterals();
     if (config->icfLevel != ICFLevel::none) {
       if (config->icfLevel == ICFLevel::safe)
         markAddrSigSymbols();
       foldIdenticalSections(/*onlyCfStrings=*/false);

lld/MachO/Options.td

def ignore_auto_link_option : Separate<["--"], "ignore-auto-link-option">,
     Group<grp_lld>;
 def ignore_auto_link_option_eq : Joined<["--"], "ignore-auto-link-option=">,
     Alias<!cast<Separate>(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>;
 
 // 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/objc-category-conflicts.s

 # REQUIRES: x86
 # RUN: rm -rf %t; split-file %s %t
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-macos11.0 -I %t %t/cat1.s -o %t/cat1.o
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-macos11.0 -I %t %t/cat2.s -o %t/cat2.o
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-macos11.0 -I %t %t/klass.s -o %t/klass.o
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-macos11.0 -I %t %t/cat1.s --defsym MAKE_LOAD_METHOD=1 -o %t/cat1-with-load.o
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-macos11.0 -I %t %t/cat2.s --defsym MAKE_LOAD_METHOD=1 -o %t/cat2-with-load.o
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-macos11.0 -I %t %t/klass.s --defsym MAKE_LOAD_METHOD=1 -o %t/klass-with-load.o
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-macos11.0 -I %t %t/klass-with-no-rodata.s -o %t/klass-with-no-rodata.o
 # RUN: %lld -dylib -lobjc %t/klass.o -o %t/libklass.dylib
 
-# RUN: %no-fatal-warnings-lld -dylib -lobjc %t/klass.o %t/cat1.o %t/cat2.o -o \
+# RUN: %no-fatal-warnings-lld --check-category-conflicts -dylib -lobjc %t/klass.o %t/cat1.o %t/cat2.o -o \
 # RUN:   /dev/null 2>&1 | FileCheck %s --check-prefixes=CATCLS,CATCAT
-# RUN: %no-fatal-warnings-lld -dylib -lobjc %t/libklass.dylib %t/cat1.o \
+# RUN: %no-fatal-warnings-lld --check-category-conflicts -dylib -lobjc %t/libklass.dylib %t/cat1.o \
 # RUN:   %t/cat2.o -o /dev/null 2>&1 | FileCheck %s --check-prefix=CATCAT
 
 ## Check that we don't emit spurious warnings around the +load method while
 ## still emitting the other warnings. Note that we have made separate
 ## `*-with-load.s` files for ease of comparison with ld64; ld64 will not warn
 ## at all if multiple +load methods are present.
-# RUN: %no-fatal-warnings-lld -dylib -lobjc %t/klass-with-load.o \
+# RUN: %no-fatal-warnings-lld --check-category-conflicts -dylib -lobjc %t/klass-with-load.o \
 # RUN:   %t/cat1-with-load.o %t/cat2-with-load.o -o /dev/null 2>&1 | \
 # RUN:   FileCheck %s --check-prefixes=CATCLS,CATCAT --implicit-check-not '+load'
 
 ## Regression test: Check that we don't crash.
-# RUN: %no-fatal-warnings-lld -dylib -lobjc %t/klass-with-no-rodata.o -o /dev/null
+# RUN: %no-fatal-warnings-lld --check-category-conflicts -dylib -lobjc %t/klass-with-no-rodata.o -o /dev/null
+
+## Check that we don't emit any warnings without --check-category-conflicts.
+# RUN: %no-fatal-warnings-lld -dylib -lobjc %t/klass.o %t/cat1.o %t/cat2.o -o \
+# RUN:   /dev/null 2>&1 | FileCheck %s --implicit-check-not 'warning' --allow-empty
 
 # CATCLS:      warning: method '+s1' has conflicting definitions:
 # CATCLS-NEXT: >>> defined in category Cat1 from {{.*}}cat1{{.*}}.o
 # CATCLS-NEXT: >>> defined in class Foo from {{.*}}klass{{.*}}.o
 
 # CATCLS:      warning: method '-m1' has conflicting definitions:
 # CATCLS-NEXT: >>> defined in category Cat1 from {{.*}}cat1{{.*}}.o
 # CATCLS-NEXT: >>> defined in class Foo from {{.*}}klass{{.*}}.o