[llvm-driver] Add lld

[abrachet]

Summary

The llvm-driver, enabled with LLVM_TOOL_LLVM_DRIVER_BUILD combines many llvm executables
into one to save overall toolchain size. This patch adds the capability for lld to be part of the
llvm-driver.

[MaskRay]

Please add -DLLVM_TOOL_LLVM_DRIVER_BUILD=on to the summary. [llvm-driver] isn't clear.

Note: by using this, we lose the property to make clang and lld separately profile-guided optimized.

Since you work at Google, can I request that you fix llvm-project-overlay/lld/BUILD.bazel similar to llvm-project-overlay/clang/BUILD.bazel clang_main?
Otherwise it would cause some integration trouble...

llvm/test/tools/llvm-driver/passthrough-lld.test

5

may not be necessary to test -15 variants.

[MaskRay]

Ping

[abrachet]

I was considering holding off on this patch till after D127800 so that the diff would be simpler there. Or would you rather move ahead here first?

[abrachet]

In D127472#3575182, @MaskRay wrote:

Please add -DLLVM_TOOL_LLVM_DRIVER_BUILD=on to the summary. [llvm-driver] isn't clear.

Done

Note: by using this, we lose the property to make clang and lld separately profile-guided optimized.

Yeah, that's a good observation I hadn't thought about. Likely the way clang and lld utilize libObject is very different for example. I can look into adding something along the lines of a LLVM_DRIVER_EXCLUDE_TOOLS list so it can chosen if some tools should be omitted.

Since you work at Google, can I request that you fix llvm-project-overlay/lld/BUILD.bazel similar to llvm-project-overlay/clang/BUILD.bazel clang_main?
Otherwise it would cause some integration trouble...

Done

In D127472#3610252, @abrachet wrote:

I was considering holding off on this patch till after D127800 so that the diff would be simpler there. Or would you rather move ahead here first?

It actually didn't complicate things at all...

[MaskRay]

lld/include/lld/Common/Driver.h

28 ↗

(On Diff #465822)

Seem unnecessary?

[abrachet]

lld/include/lld/Common/Driver.h

28 ↗

(On Diff #465822)

I don't understand why, but T** doesn't implicitly convert to const T **, and the only way I could find to add the const qualifier to the inner pointer was through const_cast so I can either keep this as const char ** and const_cast in from lld_main or keep this as char **. WDYT?

[MaskRay]

lld/include/lld/Common/Driver.h

28 ↗

(On Diff #465822)

This should be fine. const is the preferred one (I just want to decouple unrelated changes....)

lld/tools/lld/CMakeLists.txt

 set(LLVM_LINK_COMPONENTS
   Support
   )
 
 add_lld_tool(lld
   lld.cpp
 
   SUPPORT_PLUGINS
+  GENERATE_DRIVER
   )
 export_executable_symbols_for_plugins(lld)
 
-target_link_libraries(lld
+function(lld_target_link_libraries target type)
+  target_link_libraries(${target} ${type} ${ARGN})
+  if (TARGET obj.${target})
+    target_link_libraries(obj.${target} ${ARGN})
+  endif()
+endfunction()
+
+lld_target_link_libraries(lld
   PRIVATE
   lldCommon
   lldCOFF
   lldELF
   lldMachO
   lldMinGW
   lldWasm
   )

lld/tools/lld/lld.cpp

 // signifies that LLD shall not release any memory after execution, to speed up
 // process destruction.
 static unsigned inTestVerbosity() {
   unsigned v = 0;
   StringRef(getenv("LLD_IN_TEST")).getAsInteger(10, v);
   return v;
 }
 
-int main(int argc, const char **argv) {
+int lld_main(int argc, char **argv) {
   InitLLVM x(argc, argv);
   sys::Process::UseANSIEscapeCodes(true);
 
   if (::getenv("FORCE_LLD_DIAGNOSTICS_CRASH")) {
     llvm::errs()
         << "crashing due to environment variable FORCE_LLD_DIAGNOSTICS_CRASH\n";
     LLVM_BUILTIN_TRAP;
   }
 
   // Not running in lit tests, just take the shortest codepath with global
   // exception handling and no memory cleanup on exit.
   if (!inTestVerbosity())
-    return lldMain(argc, argv, llvm::outs(), llvm::errs());
+    return lldMain(argc, const_cast<const char **>(argv), llvm::outs(),
+                   llvm::errs());
 
   Optional<int> mainRet;
   CrashRecoveryContext::Enable();
 
   for (unsigned i = inTestVerbosity(); i > 0; --i) {
     // Disable stdout/stderr for all iterations but the last one.
     inTestOutputDisabled = (i != 1);
 
     // Execute one iteration.
-    auto r = safeLldMain(argc, argv, llvm::outs(), llvm::errs());
+    auto r = safeLldMain(argc, const_cast<const char **>(argv), llvm::outs(),
+                         llvm::errs());
     if (!r.canRunAgain)
       exitLld(r.ret); // Exit now, can't re-execute again.
 
     if (!mainRet) {
       mainRet = r.ret;
     } else if (r.ret != *mainRet) {
       // Exit now, to fail the tests if the result is different between runs.
       return r.ret;
     }
   }
   return *mainRet;
 }

llvm/test/tools/llvm-driver/lit.local.cfg

+from lit.llvm import llvm_config
+
+if llvm_config.use_lld(required=False):
+    config.available_features.add('lld')

llvm/test/tools/llvm-driver/passthrough-lld.test

+# REQUIRES: lld
+
+# RUN: %llvm ld.lld --help | FileCheck %s
+# RUN: %llvm lld -flavor ld.lld --help | FileCheck %s
+
+# CHECK: supported targets: elf

llvm/tools/llvm-driver/llvm-driver.cpp

static int findTool(int Argc, char **Argv) {
 
   if (ToolName == "--help") {
     printHelpMessage();
     return 0;
   }
 
   StringRef Stem = sys::path::stem(ToolName);
   auto Is = [=](StringRef Tool) {
+    auto IsImpl = [=](StringRef Stem) {
       auto I = Stem.rfind_insensitive(Tool);
       return I != StringRef::npos && (I + Tool.size() == Stem.size() ||
                                       !llvm::isAlnum(Stem[I + Tool.size()]));
     };
+    for (StringRef S : {Stem, ToolName})
+      if (IsImpl(S))
+        return true;
+    return false;
+  };
 
 #define LLVM_DRIVER_TOOL(tool, entry)                                          \
   if (Is(tool))                                                                \
     return entry##_main(Argc, Argv);
 #include "LLVMDriverTools.def"
 
   if (Is("llvm"))
     return findTool(Argc - 1, Argv + 1);

utils/bazel/llvm-project-overlay/lld/BUILD.bazel

 # This file is licensed under the Apache License v2.0 with LLVM Exceptions.
 # See https://llvm.org/LICENSE.txt for license information.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
+load("@bazel_skylib//rules:expand_template.bzl", "expand_template")
 load("//llvm:tblgen.bzl", "gentbl")
 
 package(
     default_visibility = ["//visibility:public"],
 )
 
 licenses(["notice"])
 
deps = [
         "//llvm:Core",
         "//llvm:LTO",
         "//llvm:Object",
         "//llvm:Option",
         "//llvm:Support",
     ],
 )
 
+expand_template(
+    name = "lld_main",
+    out = "lld-driver.cpp",
+    substitutions = {
+        "@TOOL_NAME@": "lld",
+    },
+    template = "//llvm:cmake/modules/llvm-driver-template.cpp.in",
+)
+
 cc_binary(
     name = "lld",
     srcs = glob([
         "tools/lld/*.cpp",
         "tools/lld/*.h",
-    ]),
+    ]) + ["lld-driver.cpp"],
     deps = [
         ":COFF",
         ":Common",
         ":ELF",
         ":MachO",
         ":MinGW",
         ":Wasm",
         "//llvm:Support",