[lld-macho] Initialize LTO backend with diagnostic handler

[int3]

Summary

Failing to do so results in std::bad_function_call being
thrown when a pass tries to emit a diagnostic.

I've copied the relevant test over from LLD-ELF's test suite.

[int3]

rebase

[thevinster]

Thanks! This seems to check out with the stack trace line that I was seeing.

8 ld64.lld 0x0000000103aeca10 llvm::LLVMContext::diagnose(llvm::DiagnosticInfo const&) + 96

I see from the tests in LLD-ELF that it's separated LTO tests in to its own folder. I'm wondering if we should also do the same for the MachO port? I don't have any strong opinions either ways other than consistency with the ELF port.

[int3]

I intentionally put the tests in a single folder because I didn't really see the value of a subfolder... all our lto tests are prefixed by lto-, so they're easy to glob for anyway. Also, a lot of the ELF tests were written before split-file became available, so they have a lot of extra files under Inputs, and I guess that gets messy after a while without breaking things up into subfolders.

lld/MachO/LTO.cpp

 using namespace llvm::sys;
 
 static lto::Config createConfig() {
   lto::Config c;
   c.Options = initTargetOptionsFromCodeGenFlags();
   c.CodeModel = getCodeModelFromCMModel();
   c.CPU = getCPUStr();
   c.MAttrs = getMAttrs();
+  c.DiagHandler = diagnosticHandler;
   c.UseNewPM = config->ltoNewPassManager;
   c.PreCodeGenPassesHook = [](legacy::PassManager &pm) {
     pm.add(createObjCARCContractPass());
   };
   c.TimeTraceEnabled = config->timeTraceEnabled;
   c.TimeTraceGranularity = config->timeTraceGranularity;
   c.OptLevel = config->ltoo;
   c.CGOptLevel = args::getCGOptLevel(config->ltoo);

lld/test/MachO/lto-irmover-warning.ll

+; REQUIRES: x86
+; RUN: rm -rf %t; split-file %s %t
+; RUN: llvm-as -o %t/first.bc %t/first.ll
+; RUN: llvm-as -o %t/second.bc %t/second.ll
+; RUN: %no_fatal_warnings_lld -dylib %t/first.bc %t/second.bc -o /dev/null 2>&1 | FileCheck %s
+
+;; FIXME: can we replace ld-temp.o with a proper name?
+; CHECK: warning: linking module flags 'foo': IDs have conflicting values ('i32 2' from {{.*}}second.bc with 'i32 1' from ld-temp.o)
+
+;--- first.ll
+target triple = "x86_64-apple-macosx10.15.0"
+target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+
+declare void @f()
+
+define void @g() {
+  call void @f()
+  ret void
+}
+
+!0 = !{ i32 2, !"foo", i32 1 }
+
+!llvm.module.flags = !{ !0 }
+
+;--- second.ll
+target triple = "x86_64-apple-macosx10.15.0"
+target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+
+define void @f() {
+  ret void
+}
+
+!0 = !{ i32 2, !"foo", i32 2 }
+
+!llvm.module.flags = !{ !0 }