IR: Add assembly/bitcode support for function metadata attachments

Add serialization support for function metadata attachments (added in
r235783).  The syntax is:

    define @foo() !attach !0 {

Metadata attachments are only allowed on functions with bodies.  Since
they come before the `{`, they're not really part of the body; since
they require a body, they're not really part of the header.  In
`LLParser` I gave them a separate function called from `ParseDefine()`,
`ParseOptionalFunctionMetadata()`.

In bitcode, I'm using the same `METADATA_ATTACHMENT` record used by
instructions.  Instruction metadata attachments are included in a
special "attachment" block at the end of a `Function`.  The attachment
records are laid out like this:

    InstID (KindID MetadataID)+

Note that these records always have an odd number of fields.  The new
code takes advantage of this to recognize function attachments (which
don't need an instruction ID):

    (KindID MetadataID)+

This means we can use the same attachment block already used for
instructions.

This is part of PR23340.

llvm-svn: 235785

1 files changed, 14 insertions, 0 deletions

diff --git a/llvm/test/Assembler/metadata.ll b/llvm/test/Assembler/metadata.ll
index b483fc3f4cf..21a47ddb734 100644
--- a/llvm/test/Assembler/metadata.ll
+++ b/llvm/test/Assembler/metadata.ll
@@ -11,8 +11,22 @@ define void @test() {
   ret void, !foo !0, !bar !1
 }
 
+; CHECK: define void @test2() !foo !2 !baz !3
+define void @test2() !foo !2 !baz !3 {
+  unreachable
+}
+
+; CHECK: define void @test3() !bar !3
+; CHECK: unreachable, !bar !4
+define void @test3() !bar !3 {
+  unreachable, !bar !4
+}
+
 !0 = !MDLocation(line: 662302, column: 26, scope: !1)
 !1 = !MDSubprogram(name: "foo")
+!2 = distinct !{}
+!3 = distinct !{}
+!4 = distinct !{}
 
 declare void @llvm.dbg.func.start(metadata) nounwind readnone