ellis added a comment.
In D157913#4626007 <https://reviews.llvm.org/D157913#4626007>, @zequanwu wrote:
>> It seems that the `__llvm_prf_names` is retained in this mode. What is the
>> overhead of this section generally? Can we instead use debug info to lookup
>> function names?
>
> With debug info correlation enabled, `__llvm_prf_names` section will only
> contain functions names that are not emitted to the final binary, not even in
> debug info. So, this section is still much smaller compared to when not
> enabling debug info correlation. This is used to indicate that those
> functions are covered but not executed.
>
> Example from the test case above:
>
> $ cat a.cpp
> struct A {
> void unused_func() {}
> };
> void used_func() {}
> int main() {
> used_func();
> return 0;
> }
> $ clang -fprofile-instr-generate -fcoverage-mapping -mllvm
> -enable-name-compression=false -mllvm -debug-info-correlate -g a.cpp -o a.out
> $ llvm-objdump --section=__llvm_prf_names --full-contents a.out
>
> a.out: file format elf64-x86-64
> Contents of section __llvm_prf_names:
> 7b65 14005f5a 4e314131 31756e75 7365645f .._ZN1A11unused_
> 7b75 66756e63 4576 funcEv
Thanks for the explanation!
================
Comment at: clang/test/CodeGen/coverage-debug-info-correlate.c:1
+// RUN: %clang_cc1 -debug-info-kind=standalone -mllvm -debug-info-correlate
-fprofile-instrument=clang -fcoverage-mapping -emit-llvm -o - %s | FileCheck %s
+
----------------
I think this test can be generalized to check that `__llvm_profile_raw_version`
is emitted with or without debug info correlation.
================
Comment at: compiler-rt/test/profile/Darwin/coverage-debug-info-correlate.cpp:9
+// RUN: %clang_profgen -o %t -g -mllvm --debug-info-correlate
-fcoverage-mapping %S/../Inputs/instrprof-debug-info-correlate-main.cpp
%S/../Inputs/instrprof-debug-info-correlate-foo.cpp
+// RUN: env LLVM_PROFILE_FILE=%t.profraw %run %t
+// RUN: llvm-profdata merge -o %t.profdata --debug-info=%t.dSYM %t.profraw
----------------
NIT
================
Comment at: compiler-rt/test/profile/Darwin/coverage-debug-info-correlate.cpp:29
+
+// RUN: llvm-cov report --instr-profile=%t.profdata %t | FileCheck %s
-check-prefix=NONAME
+
----------------
Is it worth testing that `%t.normal.profdata` emits the same coverage?
================
Comment at: llvm/lib/ProfileData/Coverage/CoverageMappingReader.cpp:1019-1029
+ if (auto E = NamesSection.takeError()) {
+ if (ProfileNames.isEmpty())
+ return std::move(E);
+ consumeError(std::move(E));
+ } else {
+ std::vector<SectionRef> NamesSectionRefs = *NamesSection;
+ if (NamesSectionRefs.size() != 1)
----------------
I don't quite understand why this was changed. Is there is a test case that
covers this?
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D157913/new/
https://reviews.llvm.org/D157913
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