[LLVMdev] RFC: ThinLTO Impementation Plan

[Xinliang David Li]

On Fri, May 15, 2015 at 2:46 PM, David Blaikie <dblaikie at gmail.com> wrote:

>
>
> 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)
>
>
To add more to the fun: C99 extern inline and gnu C behave the opposite way.

David



> 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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