[llvm-dev] ThinLTO: module-scope inline assembly blocks

[Johan Engelen via llvm-dev]

Hi all,
  I am trying to add ThinLTO to the LDC compiler. It seems to work well on
Mac (XCode 8) and Ubuntu (ld.gold + LLVMgold plugin).
However, I am running into trouble with module-scope inline assembly blocks.

I have a module ASM with a function `foo` defined in an inline assembly
block (and an LLVM IR `declare @foo()` for it). There is also a "normal"
function `void simplefunction()` defined in the module.
```
module asm "\09.text"
module asm "\09.globl\09foo"
module asm "\09.align\0916, 0x90"
module asm "\09.type\09foo, at function"
module asm "foo:"
module asm "\09movq %rdi, %rax"
module asm "\09rorw $8, %ax"
module asm "\09ret "
module asm "\09.size\09foo, .-foo"
module asm ""

declare zeroext i16 @foo(i16 zeroext) #0

define i32 @_simplefunction() #1 {
  ret i32 1
}
```

Another module MAIN contains a function that calls ASM's `simplefunction()`.
```
define i32 @_Dmain({ i64, { i64, i8* }* } %unnamed) #0 {
  %1 = call i32 @_simplefunction() #1
  ret i32 %1
}
declare i32 @_simplefunction() #1
```

Then these two modules are passed to the linker, using ThinLTO, thus
bitcode files with .o extension and module summaries added. The linker
reports a multiple definition error for the inline assembly function.
(note that `foo` is not called anywhere)

I suspect that when ThinLTO decides to import a function from another
module for inlining, the other module's module-scope assembly blocks are
also imported, which later result in the multiple definition problems.

My question: is this known, intended, or otherwise broken on _my_ end? Or
perhaps is it a bug and importing from modules with module-scope assembly
should be disabled / should not import the module-scope asm?

(I can "fix" things on my end by disabling ThinLTO when there is a
module-scope asm block, but perhaps there should be a proper fix in LLVM)

Thanks!

Cheers,
  Johan
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