[PATCH] D16947: [PGO] assignment operator does not get profile data

Mon Feb 8 15:46:44 PST 2016

On Mon, Feb 8, 2016 at 3:35 PM, David Blaikie <dblaikie at gmail.com> wrote:
>
>
> On Mon, Feb 8, 2016 at 3:21 PM, Xinliang David Li <davidxl at google.com>
> wrote:
>>
>> On Mon, Feb 8, 2016 at 3:17 PM, David Blaikie <dblaikie at gmail.com> wrote:
>> >
>> >
>> > On Mon, Feb 8, 2016 at 12:07 PM, Xinliang David Li <davidxl at google.com>
>> > wrote:
>> >>
>> >> On Mon, Feb 8, 2016 at 11:39 AM, David Blaikie <dblaikie at gmail.com>
>> >> wrote:
>> >> >
>> >> >
>> >> > On Mon, Feb 8, 2016 at 9:25 AM, David Li via llvm-commits
>> >> > <llvm-commits at lists.llvm.org> wrote:
>> >> >>
>> >> >> davidxl updated this revision to Diff 47217.
>> >> >> davidxl added a comment.
>> >> >>
>> >> >> Simplified test case suggested by Vedant.
>> >> >>
>> >> >>
>> >> >> http://reviews.llvm.org/D16947
>> >> >>
>> >> >> Files:
>> >> >>   lib/CodeGen/CGClass.cpp
>> >> >>   test/Profile/def-assignop.cpp
>> >> >>
>> >> >> Index: test/Profile/def-assignop.cpp
>> >> >> ===================================================================
>> >> >> --- test/Profile/def-assignop.cpp
>> >> >> +++ test/Profile/def-assignop.cpp
>> >> >> @@ -0,0 +1,32 @@
>> >> >> +// RUN: %clang_cc1 -x c++ -std=c++11 %s -triple
>> >> >> x86_64-unknown-linux-gnu
>> >> >> -main-file-name def-assignop.cpp -o - -emit-llvm
>> >> >> -fprofile-instrument=clang
>> >> >> | FileCheck --check-prefix=PGOGEN %s
>> >> >> +// RUN: %clang_cc1 -x c++ -std=c++11 %s -triple
>> >> >> x86_64-unknown-linux-gnu
>> >> >> -main-file-name def-assignop.cpp -o - -emit-llvm
>> >> >> -fprofile-instrument=clang
>> >> >> -fcoverage-mapping | FileCheck --check-prefix=COVMAP %s
>> >> >> +
>> >> >> +struct B {
>> >> >> +  void operator=(const B &b) {}
>> >> >> +  void operator=(const B &&b) {}
>> >> >
>> >> >
>> >> > Probably best to make these canonical to avoid confusion:
>> >> >
>> >> > B &operator=(const B&);
>> >> > B &operator=(B&&);
>> >> >
>> >> > (& they don't need definitions - just declarations)
>> >>
>> >> Will change.
>> >>
>> >> >
>> >> > Also, neither of these are the move /constructor/, just the move
>> >> > operator.
>> >> > Not sure if Vedant just used the wrong terminology, or whether it's
>> >> > worth
>> >> > testing the move/copy ctors too, to check that they do the right
>> >> > thing
>> >> > as
>> >>
>> >> I added tests for copy ctors, and plan to add move ctor test soon.
>> >>
>> >> > well. (if all of these things use the same codepath, I don't see a
>> >> > great
>> >> > benefit in having separate tests for them (but you can add them here
>> >> > if
>> >> > you
>> >> > like) - I'm just suggesting a manual verification in case those need
>> >> > a
>> >> > separate fix
>> >>
>> >> the ctor and assignment op do not share the same path -- the ctor path
>> >> is working as expected without the fix -- or do you mean there is no
>> >> need to cover both copy and move variants?
>> >
>> >
>> > I wouldn't necessarily bother testing multiple instances of the same
>> > codepath (so the copy and move ctor for example) - but 2 instances is no
>> > big
>> > deal (if there were several more, I might be inclined to just test one
>> > as a
>> > representative sample). I don't mind either way, though. The number is
>> > small
>> > & the test cases are arguably distinct.
>>
>> Sorry I disagree with your general statement here. I treat such test
>> cases as 'black box testing' that do not know about the internal
>> implementation (code path). It may or may not share the same code path
>> today -- same is true in the future.
>
>
> While there's merit in both approaches, practically speaking it seems
> difficult to test in that way in general - any feature could interact with
> any other.

The language features are well specified -- so writing small test
cases to cover them is a general accepted way of testing.

>The LLVM regression suite is far more narrowly targeted than that
> - we don't test combinations of optimizations, for example - we test each
> optimization in isolation. The same would be true of two independent
> features on an interface such as this, I think.

This is a weakness of the test system -- a problem at a different dimension.

>
>>
>>
>> >
>> >>
>> >> >
>> >> >>
>> >> >> +};
>> >> >> +
>> >> >> +struct A {
>> >> >> +  A &operator=(const A &) = default;
>> >> >
>> >> >
>> >> > Is the fix/codepath specifically about explicitly defaulted ops?
>> >>
>> >> yes -- explicitly defaulted. There are some test coverage already for
>> >> implicitly declared ctors (but not assignment op -- probably worth
>> >> adding some testing too).
>> >
>> >
>> > Hmm - are you sure there's no common codepath that would cover the
>> > explicitly defaulted or implicitly defaulted ops together in one go?
>>
>> Sorry I am not sure what you mean here.
> Is there some part of Clang that is responsible for generating both
> implicitly defaulted and explicitly defaulted move/copy ops that could
> handle this case, rather than apparently handling the implicit and explicit
> cases separately (it seems they're being handled separately if the implicit
> case worked before and you added code (rather than moving code) to fix the
> explicit case - it sounds like we now have two bits of code, one for
> implicit and one for explicit - perhaps there's a single bit of code that we
> could write that would handle both?)

The codegen paths are different -- otherwise as you commented, the
implicit case would have been broken too.

Refactoring FE code to handle both is probably beyond the scope of
this fix.  Having a good test case here will exactly help avoid
regression if that happens in the future.

David

>
> - David
>
>>
>>
>> David
>>
>> >
>> >>
>> >>
>> >> > Or just any
>> >> > compiler-generated ones? (you could drop these lines if it's about
>> >> > any
>> >> > compiler-generated ones, might be simpler/more obvious that it's not
>> >> > about
>> >> > the "= default" feature)
>> >>
>> >> Other compiler generated ones are handled differently.
>> >>
>> >> thanks,
>> >>
>> >> David
>> >>
>> >> >
>> >> >>
>> >> >> +  // PGOGEN: define {{.*}}@_ZN1AaSERKS_(
>> >> >> +  // PGOGEN: %pgocount = load {{.*}} @__profc__ZN1AaSERKS_
>> >> >> +  // PGOGEN: {{.*}}add{{.*}}%pgocount, 1
>> >> >> +  // PGOGEN: store{{.*}}@__profc__ZN1AaSERKS_
>> >> >> +  A &operator=(A &&) = default;
>> >> >>
>> >> >> +  // PGOGEN: define {{.*}}@_ZN1AaSEOS_
>> >> >> +  // PGOGEN: %pgocount = load {{.*}} @__profc__ZN1AaSEOS_
>> >> >> +  // PGOGEN: {{.*}}add{{.*}}%pgocount, 1
>> >> >> +  // PGOGEN: store{{.*}}@__profc__ZN1AaSEOS_
>> >> >> +
>> >> >> +  // Check that coverage mapping includes 6 function records
>> >> >> including
>> >> >> the
>> >> >> +  // defaulted copy and move operators: A::operator=
>> >> >> +  // COVMAP: @__llvm_coverage_mapping = {{.*}} { { i32, i32, i32,
>> >> >> i32
>> >> >> },
>> >> >> [5 x <{{.*}}>],
>> >> >> +  B b;
>> >> >> +};
>> >> >> +
>> >> >> +int main() {
>> >> >> +  A a1, a2;
>> >> >> +  a1 = a2;
>> >> >> +  a2 = static_cast<A &&>(a1);
>> >> >
>> >> >
>> >> > An option, though not necessarily better, would be to just take the
>> >> > address
>> >> > of the special members:
>> >> >
>> >> > auto (B::*x)(const B&) = &bar::operator=;
>> >> > auto (B::*x)(B&&) = &bar::operator=;
>> >> >
>> >> > In short, what I'm picturing, in total:
>> >> >
>> >> > struct A {
>> >> >   A &operator=(const A&);
>> >> >   A &operator=(A&&);
>> >> > };
>> >> >
>> >> > struct B {
>> >> >   A a;
>> >> > };
>> >> >
>> >> > auto (B::*x)(const B&) = &B::operator=;
>> >> > auto (B::*x)(B&&) = &B::operator=;
>> >> >
>> >> > Also, this test should probably be in clang, since it's a clang code
>> >> > change/fix.
>> >> >
>> >> >
>> >> >>
>> >> >> +  return 0;
>> >> >> +}
>> >> >> Index: lib/CodeGen/CGClass.cpp
>> >> >> ===================================================================
>> >> >> --- lib/CodeGen/CGClass.cpp
>> >> >> +++ lib/CodeGen/CGClass.cpp
>> >> >> @@ -1608,6 +1608,7 @@
>> >> >>
>> >> >>    LexicalScope Scope(*this, RootCS->getSourceRange());
>> >> >>
>> >> >> +  incrementProfileCounter(RootCS);
>> >> >>    AssignmentMemcpyizer AM(*this, AssignOp, Args);
>> >> >>    for (auto *I : RootCS->body())
>> >> >>      AM.emitAssignment(I);
>> >> >>
>> >> >>
>> >> >>
>> >> >> _______________________________________________
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>> >> >> llvm-commits at lists.llvm.org
>> >> >> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits
>> >> >>
>> >> >
>> >
>> >
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