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

[Xinliang David Li via llvm-commits]

Both cfe-commits and llvm-commits are cc'ed.

David

On Mon, Feb 8, 2016 at 11:29 AM, David Blaikie <dblaikie at gmail.com> wrote:
> This looks like a change to clang - could you test it in clang (& review it
> on cfe-commits instead of llvm-commits)?
>
> On Sat, Feb 6, 2016 at 11:57 AM, David Li via cfe-commits
> <cfe-commits at lists.llvm.org> wrote:
>>
>> davidxl created this revision.
>> davidxl added a reviewer: vsk.
>> davidxl added subscribers: llvm-commits, cfe-commits.
>>
>> For compiler generated assignment operator that is not trivial (calling
>> base class operator=()), Clang FE assign region counters to the function
>> body but does not emit profile counter increment for the function entry.
>> This leads to many problems:
>>
>> 1) the operator body does not have profile data generated leading to
>> warning in profile-use
>> 2) the size of the function body may be large and lack of profile data may
>> lead to wrong inlining decisions
>> 3) when FE assign region counters to the function, it also emit coverage
>> mapping data for the function -- but it has no coverage data which is
>> confusing (currently the llvm-cov tool will report malformed format (as the
>> name of the operator is not put into the right name section).
>>
>> 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 +1,34 @@
>> +// RUN: %clang_cc1 -x c++ %s -triple x86_64-unknown-linux-gnu
>> -main-file-name def-assignop.cpp -o - -emit-llvm -fprofile-instrument=clang
>> | FileCheck --check-prefix=PGOGEN %s
>> +
>> +
>> +struct B {
>> +  int B;
>> +  void *operator=(const struct B &b2) {
>> +    if (b2.B == 0) {
>> +      B = b2.B + 1;
>> +    } else
>> +      B = b2.B;
>> +    return this;
>> +  }
>> +};
>> +
>> +struct A : public B {
>> +  A &operator=(const A &) = default;
>> +// PGOGEN: define {{.*}}@_ZN1AaSERKS_(
>> +// PGOGEN: %pgocount = load {{.*}} @__profc__ZN1AaSERKS_
>> +// PGOGEN: {{.*}}add{{.*}}%pgocount, 1
>> +// PGOGEN: store{{.*}}@__profc__ZN1AaSERKS_
>> +  int I;
>> +  int J;
>> +  int getI() { return I; }
>> +};
>> +
>> +A aa;
>> +int g;
>> +int main() {
>> +  A aa2;
>> +  aa2 = aa;
>> +
>> +  g = aa2.getI();
>> +  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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>