[lld][WebAssembly] Require double dash for modern linker flags

[sbc100]

Summary

This matches the behaviour of the ELF backend (in fact this change
is mostly just copying directly from ELF/Options.td).

[dschuff]

LGTM but will this require a change to clang and/or EMCC first?

[sbc100]

In D126500#3541093, @dschuff wrote:

LGTM but will this require a change to clang and/or EMCC first?

No, that would only be needed is that were not already using the double dash version. I ran that emscripten test suite and confirmed it was not using the single dash version anywhere.

lld/test/wasm/lto/atomics.ll

 ; RUN: llvm-as %s -o %t.o
-; RUN: wasm-ld %t.o -o %t.wasm -lto-O0
+; RUN: wasm-ld %t.o -o %t.wasm --lto-O0
 
 ; Atomic operations will not fail to compile if atomics are not
 ; enabled because LLVM atomics will be lowered to regular ops.
 
 target datalayout = "e-m:e-p:32:32-p10:8:8-p20:8:8-i64:64-n32:64-S128"
 target triple = "wasm32-unknown-unknown-wasm"
 
 @foo = hidden global i32 1
 
 define void @_start() {
   %1 = load atomic i32, i32* @foo unordered, align 4
   ret void
 }

lld/test/wasm/lto/pic-empty.s

 ; Test that LTO objects with no function can still be linked as shared
 ; libraries.
 ; We had a bug where the mutable-globals feature was not being added
 ; so the linker-generated import of `__stack_pointer` (which is currently
 ; mandatory for ; shared libraries) was generating a linker error.
 ; See https://bugs.llvm.org/show_bug.cgi?id=52339
 
 ; RUN: llvm-as %s -o %t.o
-; RUN: wasm-ld -lto-O2 --experimental-pic -shared --no-gc-sections --export=tls_int %t.o -o %t.so
+; RUN: wasm-ld --lto-O2 --experimental-pic -shared --no-gc-sections --export=tls_int %t.o -o %t.so
 ; RUN: obj2yaml %t.so  | FileCheck %s
 
 target datalayout = "e-m:e-p:32:32-p10:8:8-p20:8:8-i64:64-f128:64-n32:64-S128-ni:1:10:20"
 target triple = "wasm32-unknown-emscripten"
 
 @tls_int = dso_local thread_local global i32 99
 
 ; CHECK:  - Type:            CUSTOM
 ; CHECK:    Name:            target_features
 ; CHECK:    Features:
 ; CHECK:      - Prefix:          USED
 ; CHECK:        Name:            mutable-globals

lld/wasm/Options.td

 include "llvm/Option/OptParser.td"
 
+// Convenience classes for long options which only accept two dashes. For lld
+// specific or newer long options, we prefer two dashes to avoid collision with
+// short options. For many others, we have to accept both forms to be compatible
+// with GNU ld.
+class FF<string name> : Flag<["--"], name>;
+class JJ<string name>: Joined<["--"], name>;
+
+multiclass EEq<string name, string help> {
+  def NAME: Separate<["--"], name>;
+  def NAME # _eq: Joined<["--"], name # "=">, Alias<!cast<Separate>(NAME)>,
+    HelpText<help>;
+}
+
+multiclass BB<string name, string help1, string help2> {
+  def NAME: Flag<["--"], name>, HelpText<help1>;
+  def no_ # NAME: Flag<["--"], "no-" # name>, HelpText<help2>;
+}
+
 // For options whose names are multiple letters, either one dash or
 // two can precede the option name except those that start with 'o'.
 class F<string name>: Flag<["--", "-"], name>;
 class J<string name>: Joined<["--", "-"], name>;
 class S<string name>: Separate<["--", "-"], name>;
 
 multiclass Eq<string name, string help> {
   def NAME: Separate<["--", "-"], name>;
   def NAME # _eq: Joined<["--", "-"], name # "=">, Alias<!cast<Separate>(NAME)>,
     HelpText<help>;
 }
 
 multiclass B<string name, string help1, string help2> {
   def NAME: Flag<["--", "-"], name>, HelpText<help1>;
   def no_ # NAME: Flag<["--", "-"], "no-" # name>, HelpText<help2>;
 }
 
-multiclass BB<string name, string help1, string help2> {
-  def NAME: Flag<["--"], name>, HelpText<help1>;
-  def no_ # NAME: Flag<["--"], "no-" # name>, HelpText<help2>;
-}
-
 // The following flags are shared with the ELF linker
 def Bsymbolic: F<"Bsymbolic">, HelpText<"Bind defined symbols locally">;
 
 defm color_diagnostics: B<"color-diagnostics",
   "Alias for --color-diagnostics=always",
   "Alias for --color-diagnostics=never">;
 def color_diagnostics_eq: J<"color-diagnostics=">,
   HelpText<"Use colors in diagnostics (default: auto)">,

 
 defm export_dynamic: B<"export-dynamic",
     "Put symbols in the dynamic symbol table",
     "Do not put symbols in the dynamic symbol table (default)">;
 
 def entry: S<"entry">, MetaVarName<"<entry>">,
   HelpText<"Name of entry point symbol">;
 
-def error_limit: J<"error-limit=">,
-  HelpText<"Maximum number of errors to emit before stopping (0 = no limit)">;
+defm error_limit:
+  EEq<"error-limit", "Maximum number of errors to emit before stopping (0 = no limit)">;
 
 def fatal_warnings: F<"fatal-warnings">,
   HelpText<"Treat warnings as errors">;
 
 defm gc_sections: B<"gc-sections",
     "Enable garbage collection of unused sections",
     "Disable garbage collection of unused sections">;
 
-defm merge_data_segments: B<"merge-data-segments",
+defm merge_data_segments: BB<"merge-data-segments",
     "Enable merging data segments",
     "Disable merging data segments">;
 
 def help: F<"help">, HelpText<"Print option help">;
 
 def l: JoinedOrSeparate<["-"], "l">, MetaVarName<"<libName>">,
   HelpText<"Root name of library to use">;
 
 def L: JoinedOrSeparate<["-"], "L">, MetaVarName<"<dir>">,
   HelpText<"Add a directory to the library search path">;
 
 def m: JoinedOrSeparate<["-"], "m">, HelpText<"Set target emulation">;
 
-def mllvm: S<"mllvm">, HelpText<"Options to pass to LLVM">;
+defm mllvm: Eq<"mllvm", "Additional arguments to forward to LLVM's option processing">;
 
 defm Map: Eq<"Map", "Print a link map to the specified file">;
 
 def no_fatal_warnings: F<"no-fatal-warnings">;
 
 def o: JoinedOrSeparate<["-"], "o">, MetaVarName<"<path>">,
   HelpText<"Path to file to write output">;
 
 def O: JoinedOrSeparate<["-"], "O">, HelpText<"Optimize output file size">;
 
 defm pie: B<"pie",
     "Create a position independent executable",
     "Do not create a position independent executable (default)">;
 
 defm print_gc_sections: B<"print-gc-sections",
     "List removed unused sections",
     "Do not list removed unused sections">;
 
 def print_map: F<"print-map">,
   HelpText<"Print a link map to the standard output">;
 
 def relocatable: F<"relocatable">, HelpText<"Create relocatable object file">;
 
-defm reproduce: Eq<"reproduce", "Dump linker invocation and input files for debugging">;
+defm reproduce: EEq<"reproduce", "Dump linker invocation and input files for debugging">;
 
 defm rsp_quoting: Eq<"rsp-quoting", "Quoting style for response files">,
   MetaVarName<"[posix,windows]">;
 
 def shared: F<"shared">, HelpText<"Build a shared object">;
 
 def strip_all: F<"strip-all">, HelpText<"Strip all symbols">;
 

 def allow_undefined_file_s: Separate<["-"], "allow-undefined-file">,
   Alias<allow_undefined_file>;
 
 defm export: Eq<"export", "Force a symbol to be exported">;
 
 defm export_if_defined: Eq<"export-if-defined",
      "Force a symbol to be exported, if it is defined in the input">;
 
-def export_all: F<"export-all">,
+def export_all: FF<"export-all">,
   HelpText<"Export all symbols (normally combined with --no-gc-sections)">;
 
-def export_table: F<"export-table">,
+def export_table: FF<"export-table">,
   HelpText<"Export function table to the environment">;
 
-def growable_table: F<"growable-table">,
+def growable_table: FF<"growable-table">,
   HelpText<"Remove maximum size from function table, allowing table to grow">;
 
-def global_base: J<"global-base=">,
+def global_base: JJ<"global-base=">,
   HelpText<"Where to start to place global data">;
 
-def import_memory: F<"import-memory">,
+def import_memory: FF<"import-memory">,
   HelpText<"Import memory from the environment">;
 
-def shared_memory: F<"shared-memory">,
+def shared_memory: FF<"shared-memory">,
   HelpText<"Use shared linear memory">;
 
-def import_table: F<"import-table">,
+def import_table: FF<"import-table">,
   HelpText<"Import function table from the environment">;
 
-def initial_memory: J<"initial-memory=">,
+def initial_memory: JJ<"initial-memory=">,
   HelpText<"Initial size of the linear memory">;
 
-def max_memory: J<"max-memory=">,
+def max_memory: JJ<"max-memory=">,
   HelpText<"Maximum size of the linear memory">;
 
-def no_entry: F<"no-entry">,
+def no_entry: FF<"no-entry">,
   HelpText<"Do not output any entry point">;
 
-def stack_first: F<"stack-first">,
+def stack_first: FF<"stack-first">,
   HelpText<"Place stack at start of linear memory rather than after data">;
 
 defm whole_archive: B<"whole-archive",
     "Force load of all members in a static library",
     "Do not force load of all members in a static library (default)">;
 
-defm check_features: B<"check-features",
+defm check_features: BB<"check-features",
     "Check feature compatibility of linked objects (default)",
     "Ignore feature compatibility of linked objects">;
 
 def features: CommaJoined<["--", "-"], "features=">,
   HelpText<"Comma-separated used features, inferred from input objects by default.">;
 
 // Aliases
 def: JoinedOrSeparate<["-"], "e">, Alias<entry>;
 def: J<"entry=">, Alias<entry>;
 def: Flag<["-"], "E">, Alias<export_dynamic>, HelpText<"Alias for --export-dynamic">;
 def: Flag<["-"], "i">, Alias<initial_memory>;
 def: Flag<["-"], "M">, Alias<print_map>, HelpText<"Alias for --print-map">;
 def: Flag<["-"], "r">, Alias<relocatable>;
 def: Flag<["-"], "s">, Alias<strip_all>, HelpText<"Alias for --strip-all">;
 def: Flag<["-"], "S">, Alias<strip_debug>, HelpText<"Alias for --strip-debug">;
 def: Flag<["-"], "t">, Alias<trace>, HelpText<"Alias for --trace">;
 def: JoinedOrSeparate<["-"], "y">, Alias<trace_symbol>, HelpText<"Alias for --trace-symbol">;
 def: JoinedOrSeparate<["-"], "u">, Alias<undefined>;
 
 // LTO-related options.
-def lto_O: J<"lto-O">, MetaVarName<"<opt-level>">,
+def lto_O: JJ<"lto-O">, MetaVarName<"<opt-level>">,
   HelpText<"Optimization level for LTO">;
-def lto_partitions: J<"lto-partitions=">,
+def lto_partitions: JJ<"lto-partitions=">,
   HelpText<"Number of LTO codegen partitions">;
 def disable_verify: F<"disable-verify">;
 def save_temps: F<"save-temps">, HelpText<"Save intermediate LTO compilation results">;
-def thinlto_cache_dir: J<"thinlto-cache-dir=">,
+def thinlto_cache_dir: JJ<"thinlto-cache-dir=">,
   HelpText<"Path to ThinLTO cached object file directory">;
-defm thinlto_cache_policy: Eq<"thinlto-cache-policy", "Pruning policy for the ThinLTO cache">;
-def thinlto_jobs: J<"thinlto-jobs=">,
+defm thinlto_cache_policy: EEq<"thinlto-cache-policy", "Pruning policy for the ThinLTO cache">;
+def thinlto_jobs: JJ<"thinlto-jobs=">,
   HelpText<"Number of ThinLTO jobs. Default to --threads=">;
-def no_lto_legacy_pass_manager: F<"no-lto-legacy-pass-manager">,
+def no_lto_legacy_pass_manager: FF<"no-lto-legacy-pass-manager">,
   HelpText<"Use new pass manager">;
-def lto_debug_pass_manager: F<"lto-debug-pass-manager">,
+def lto_debug_pass_manager: FF<"lto-debug-pass-manager">,
   HelpText<"Debug new pass manager">;
 
 // Experimental PIC mode.
-def experimental_pic: F<"experimental-pic">,
+def experimental_pic: FF<"experimental-pic">,
   HelpText<"Enable Experimental PIC">;