[LTO] Improve readability of module IDs

[ikudrin]

Summary

Module IDs can appear in diagnostic messages.
This patch adds some auxiliary symbols to improve their readability.

[grimar]

My minor concern is that the new message is a bit inconsistent with our other error messages I think.

For example, we have:
{{.*}}.a({{.*}}.o): corrupted ELF file: invalid data encoding

i.e. it is <archive name>(<object name>)

and in your message you have different format:

<archive name>:<offset>(<object name>)

So I would suggest to make it <archive name>(<object name> at <offset>) or <archive name>(<object name>:<offset>) probably.

I think Rui might have a opinion here about how the error message should look like.

[ruiu]

I think I agree with George. Looks like <archive name>(<object name> at <offset>) is slightly more readable than <archive name>(<object name>:<offset>), but that's not a strong preference.

[ikudrin]

• Changed the format to <archive name>(<object name> at <offset>);
• Changed "if" to "?:";
• Simplified a check in the tests.

[grimar]

LGTM

[ruiu]

LGTM

ELF/InputFiles.cpp

if (Config->ThinLTOIndexOnly)
     Path = replaceThinLTOSuffix(MB.getBufferIdentifier());
 
   // ThinLTO assumes that all MemoryBufferRefs given to it have a unique
   // name. If two archives define two members with the same name, this
   // causes a collision which result in only one of the objects being taken
   // into consideration at LTO time (which very likely causes undefined
   // symbols later in the link stage). So we append file offset to make
   // filename unique.
-  MemoryBufferRef MBRef(
-      MB.getBuffer(),
-      Saver.save(ArchiveName + Path +
-                 (ArchiveName.empty() ? "" : utostr(OffsetInArchive))));
+  StringRef Name;
+  if (ArchiveName.empty())
+    Name = Saver.save(Path);
+  else
+    Name = Saver.save(ArchiveName + ":" + utostr(OffsetInArchive) +
+                      "(" + Path + ")");
+  MemoryBufferRef MBRef(MB.getBuffer(), Name);
 
   Obj = CHECK(lto::InputFile::create(MBRef), this);
 
   Triple T(Obj->getTargetTriple());
   EKind = getBitcodeELFKind(T);
   EMachine = getBitcodeMachineKind(MB.getBufferIdentifier(), T);
 }
 

test/ELF/lto/Inputs/irmover-warning.ll

+target triple = "x86_64-unknown-linux-gnu"
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+
+define void @f() {
+  ret void
+}
+
+!0 = !{ i32 2, !"foo", i32 2 }
+
+!llvm.module.flags = !{ !0 }

test/ELF/lto/irmover-warning.ll

+; RUN: llvm-as -o %t1.bc %s
+; RUN: llvm-as -o %t2.bc %S/Inputs/irmover-warning.ll
+; RUN: rm -f %t.a
+; RUN: llvm-ar rcs %t.a %t2.bc
+; RUN: ld.lld %t1.bc %t.a -o %t 2>&1 | FileCheck %s
+
+; CHECK: warning: linking module flags 'foo': IDs have conflicting values ('i32 2' from {{.*}}irmover-warning.ll.tmp.a:{{[0-9]+}}(irmover-warning.ll.tmp2.bc) with 'i32 1' from ld-temp.o)
+
+target triple = "x86_64-unknown-linux-gnu"
+target datalayout = "e-m:e-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 }