[LLVMdev] RFC: ThinLTO Impementation Plan

[David Blaikie]

On Fri, May 15, 2015 at 2:41 PM, Duncan P. N. Exon Smith <
dexonsmith at apple.com> wrote:

>
> > On 2015-May-15, at 13:15, Teresa Johnson <tejohnson at google.com> wrote:
> >
> > What isn't clear to me is what all uses the available
> > externally linkage type currently - do you happen to know?
>
> It's used for the `inline` keyword in the C language.


I was about to say... then I see you mentioned C. C's weird inline
semantics are... weird. (but yes, available externally)

I think we also emit vtable constants as available externally to enable
some constant-prop/inlining/devirtualization.


>   If you do a
> `git grep available_externally -- test/` inside a clang checkout you
> might find some other uses.
>
> $ cat available-externally.c
> inline int foo(int i) { return i; }
> int bar(int i) { return foo(i); }
> $ clang -S -emit-llvm -O1 available-externally.c -o -
> ; ModuleID = 'available-externally.c'
> target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
> target triple = "x86_64-apple-macosx10.10.0"
>
> ; Function Attrs: nounwind readnone ssp uwtable
> define i32 @bar(i32 %i) #0 {
>   %1 = tail call i32 @foo(i32 %i)
>   ret i32 %1
> }
>
> ; Function Attrs: inlinehint nounwind readnone ssp uwtable
> define available_externally i32 @foo(i32 %i) #1 {
>   ret i32 %i
> }
>
> attributes #0 = { nounwind readnone ssp uwtable
> "less-precise-fpmad"="false" "no-frame-pointer-elim"="true"
> "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false"
> "no-nans-fp-math"="false" "stack-protector-buffer-size"="8"
> "target-cpu"="core2" "unsafe-fp-math"="false" "use-soft-float"="false" }
> attributes #1 = { inlinehint nounwind readnone ssp uwtable
> "less-precise-fpmad"="false" "no-frame-pointer-elim"="true"
> "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false"
> "no-nans-fp-math"="false" "stack-protector-buffer-size"="8"
> "target-cpu"="core2" "unsafe-fp-math"="false" "use-soft-float"="false" }
>
> !llvm.module.flags = !{!0}
> !llvm.ident = !{!1}
>
> !0 = !{i32 1, !"PIC Level", i32 2}
> !1 = !{!"Apple LLVM version 7.0.0 (clang-700.9.38.2)"}
>
>
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