[PATCH] [PATCH] Teach the Inliner about attribute optnone

[Eric Christopher]

Yep. Sounds reasonable. Might want to document that.

-eric

On Tue, Sep 10, 2013 at 10:59 AM,  <Andrea_DiBiagio at sn.scee.net> wrote:
> Hi Eric,
>
> llvm-commits-bounces at cs.uiuc.edu wrote on 10/09/2013 18:24:33:
>
>> From: Eric Christopher <echristo at gmail.com>
>>
>> While I can understand not inlining into an opt-none function, why not
>> allow it to be inlined into other functions? Note that I'm not
>> objecting, just interested in the rationale.
>>
>> -eric
>>
>
> the main reason why in my opinion we shouldn't inline a optnone function
> is to guaratee that the code coming from an optnone function is never
> optimized.
> The only other alternative I can think of to guarantee this would be to
> propagate the optnone attribute to the caller function which I think is
> undesirable because the aim of the attribute is to allow a single function
> to be not optimized in the context of an otherwise optimized compilation
> unit.
>
> Does this sound reasonable to you?
>
>> On Tue, Sep 10, 2013 at 8:48 AM, Andrea Di Biagio
>> <Andrea_DiBiagio at sn.scee.net> wrote:
>> > andreadb added you to the CC list for the revision "[PATCH] Teach
>> the Inliner about attribute optnone".
>> >
>> > This patch teaches the Inliner about attribute optnone.
>> >
>> > The rules are:
>> >  * a function marked optnone is never inlined;
>> >  * only functions marked always_inline can be inlined inside a
>> function with attribute optnone.
>> >
>> > I added an LLVM test that verifies on a simple example the inliner
>> behavior with the presence of an always_inline function, an optnone
>> function and a "normal" function.
>> >
>> > Attribute optnone was originally discussed here: http://llvm.
>> 1065342.n5.nabble.com/RFC-add-Function-Attribute-to-disable-
>> optimization-td58549.html
>> >
>> > r189101 introduced attribute optnone as a function attribute.
>> > I plan to send more patches (two at least) to teach the rest of
>> the optimizer about attribute optnone and also teach clang about
>> this new attribute.
>> >
>> > Please let me know what do you think.
>> >
>> > Thanks,
>> > Andrea Di Biagio
>> >
>> > http://llvm-reviews.chandlerc.com/D1642
>> >
>> > Files:
>> >   lib/Analysis/IPA/InlineCost.cpp
>> >   test/Transforms/Inline/inline-optnone.ll
>> >
>> > Index: lib/Analysis/IPA/InlineCost.cpp
>> > ===================================================================
>> > --- lib/Analysis/IPA/InlineCost.cpp
>> > +++ lib/Analysis/IPA/InlineCost.cpp
>> > @@ -1201,6 +1201,16 @@
>> >      return llvm::InlineCost::getNever();
>> >    }
>> >
>> > +  // Never inline functions without always-inline attributes if the
>> > +  // caller has optnone attribute.
>> > +  if (CS.getCaller()->hasFnAttribute(Attribute::OptimizeNone))
>> > +    return llvm::InlineCost::getNever();
>> > +
>> > +  // Don't inline this call if the caller has the optnone attribute
>> > +  // (and the callee doesn't have always_inline, checked previously).
>> > +  if (Callee->hasFnAttribute(Attribute::OptimizeNone))
>> > +    return llvm::InlineCost::getNever();
>> > +
>> >    // Never inline functions with conflicting attributes (unless
> callee has
>> >    // always-inline attribute).
>> >    if (!functionsHaveCompatibleAttributes(CS.getCaller(), Callee))
>> > Index: test/Transforms/Inline/inline-optnone.ll
>> > ===================================================================
>> > --- test/Transforms/Inline/inline-optnone.ll
>> > +++ test/Transforms/Inline/inline-optnone.ll
>> > @@ -0,0 +1,52 @@
>> > +; RUN: opt < %s -inline -S | FileCheck %s
>> > +
>> > +; Test that functions with attribute optnone are not inlined.
>> > +; Also test that only functions with attribute alwaysinline
>> > +; are valid candidate for inlining if the caller has optnone
> attribute.
>> > +
>> > +; Function Attrs: alwaysinline nounwind readnone uwtable
>> > +define i32 @alwaysInlineFunction(i32 %a) #0 {
>> > +entry:
>> > +  %mul = mul i32 %a, %a
>> > +  ret i32 %mul
>> > +}
>> > +
>> > +; Function Attrs: nounwind readnone uwtable
>> > +define i32 @simpleFunction(i32 %a) #1 {
>> > +entry:
>> > +  %add = add i32 %a, %a
>> > +  ret i32 %add
>> > +}
>> > +
>> > +; Function Attrs: nounwind optnone readnone uwtable
>> > +define i32 @OptnoneFunction(i32 %a) #2 {
>> > +entry:
>> > +  %0 = tail call i32 @alwaysInlineFunction(i32 %a)
>> > +  %1 = tail call i32 @simpleFunction(i32 %a)
>> > +  %add = add i32 %0, %1
>> > +  ret i32 %add
>> > +}
>> > +
>> > +; CHECK-LABEL: @OptnoneFunction
>> > +; CHECK-NOT: call i32 @alwaysInlineFunction(i32 %a)
>> > +; CHECK: call i32 @simpleFunction(i32 %a)
>> > +; CHECK: ret
>> > +
>> > +; Function Attrs: nounwind readnone uwtable
>> > +define i32 @bar(i32 %a) #1 {
>> > +entry:
>> > +  %0 = tail call i32 @OptnoneFunction(i32 5)
>> > +  %1 = tail call i32 @simpleFunction(i32 6)
>> > +  %add = add i32 %0, %1
>> > +  ret i32 %add
>> > +}
>> > +
>> > +; CHECK-LABEL: @bar
>> > +; CHECK: call i32 @OptnoneFunction(i32 5)
>> > +; CHECK-NOT: call i32 @simpleFunction(i32 6)
>> > +; CHECK: ret
>> > +
>> > +
>> > +attributes #0 = { alwaysinline nounwind readnone uwtable }
>> > +attributes #1 = { nounwind readnone uwtable }
>> > +attributes #2 = { nounwind optnone readnone uwtable }
>> >
>> > _______________________________________________
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>> >
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