[llvm-dev] File/module scope inline assembly

[David Blaikie via llvm-dev]

This is roughly by design in LLVM - though other compilers have other
designs.

LLVM does not preserve the relative ordering of inline assembly and other
IR (functions, globals, etc).

"Is there anyway of writing C code that will preserve the relative ordering
of file-scoped function, data and inline-assembly definitions?" - using an
LLVM-based compiler, basically: no. Sorry :/

On Tue, Dec 12, 2017 at 5:30 AM ORiordan, Martin via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> I am trying to support an experimental DSL that uses non-C identifiers,
> but I want to write the implementation of the runtime support libraries for
> this DSL in C.  The compiler is built using the LLVM v5.0.0 release branch.
>
>
>
> To do this I thought I could simply write:
>
>
>
> int foo() { return 42; }     // The C implementation
>
> asm(".alias nonCname foo");  // Make the non-C name be a synonym for the C
> implementation
>
>
>
> If I compile with ‘-S –emit-llvm’, the LL file contains:
>
>
>
> module asm ".alias nonCname foo"
>
> define i32 @foo() local_unnamed_addr #0 {
>
>   ret i32 42
>
> }
>
>
>
> That is, the inline-assembly precedes the function definition.  The
> resulting assembly code for the target also has the ‘.alias nonCname foo’
> before the definition for the function ‘foo’.  When I edit the LL file to
> place the inline-assembly after the function definition, it makes no
> difference to the emitted assembly code for the target, it is still placed
> first.
>
>
>
> Our assembler requires that the symbol being aliased has been defined
> before the ‘.alias’ directive; but I can’t get LLVM to do this, and it
> aggregates all file-scoped (or module-scoped) inline assembly before the
> code generated for the functions and data.
>
>
>
> Since the semantics of inline-assembly are very murky, I don’t know if
> this is a bug or by-design.
>
>
>
> Is there anyway of writing C code that will preserve the relative ordering
> of file-scoped function, data and inline-assembly definitions?
>
>
>
> Thanks,
>
>
>
>             MartinO
>
>
>
>
>
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