[llvm] r258406 - [GCOV] Avoid emitting profile arcs for module and skeleton CUs

[Vedant Kumar via llvm-commits]

Hi,

I'd like to propose taking this commit for the 3.8 branch.

It stops the compiler from writing out gcov-style arc and note files for module CU's.

thanks
vedant

> On Jan 21, 2016, at 9:04 AM, Vedant Kumar via llvm-commits <llvm-commits at lists.llvm.org> wrote:
> 
> Author: vedantk
> Date: Thu Jan 21 11:04:42 2016
> New Revision: 258406
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=258406&view=rev
> Log:
> [GCOV] Avoid emitting profile arcs for module and skeleton CUs
> 
> Do not emit profile arc files and note files for module and skeleton
> CU's.
> 
> Our users report seeing unexpected *.gcda and *.gcno files in their
> projects when using gcov-style profiling with modules or frameworks.
> The unwanted files come from these modules. This is not very helpful
> for end-users. Further, we've seen reports of instrumented programs
> crashing while writing these files out (due to I/O failures).

^ We've also seen crashes because the gcda is not meant to be backwards-compatible. This results in "cannot merge previous GCDA" errors.

> 
> rdar://problem/22838296
> 
> Reviewed-by: aprantl
> 
> Differential Revision: http://reviews.llvm.org/D15997
> 
> Added:
>    llvm/trunk/test/Transforms/GCOVProfiling/modules.ll
> Modified:
>    llvm/trunk/lib/Transforms/Instrumentation/GCOVProfiling.cpp
> 
> Modified: llvm/trunk/lib/Transforms/Instrumentation/GCOVProfiling.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Instrumentation/GCOVProfiling.cpp?rev=258406&r1=258405&r2=258406&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Transforms/Instrumentation/GCOVProfiling.cpp (original)
> +++ llvm/trunk/lib/Transforms/Instrumentation/GCOVProfiling.cpp Thu Jan 21 11:04:42 2016
> @@ -494,6 +494,11 @@ void GCOVProfiler::emitProfileNotes() {
>     // LTO, we'll generate the same .gcno files.
> 
>     auto *CU = cast<DICompileUnit>(CU_Nodes->getOperand(i));
> +
> +    // Skip module skeleton (and module) CUs.
> +    if (CU->getDWOId())
> +      continue;
> +
>     std::error_code EC;
>     raw_fd_ostream out(mangleName(CU, "gcno"), EC, sys::fs::F_None);
>     std::string EdgeDestinations;
> @@ -853,6 +858,11 @@ Function *GCOVProfiler::insertCounterWri
>   if (CU_Nodes) {
>     for (unsigned i = 0, e = CU_Nodes->getNumOperands(); i != e; ++i) {
>       auto *CU = cast<DICompileUnit>(CU_Nodes->getOperand(i));
> +
> +      // Skip module skeleton (and module) CUs.
> +      if (CU->getDWOId())
> +        continue;
> +
>       std::string FilenameGcda = mangleName(CU, "gcda");
>       uint32_t CfgChecksum = FileChecksums.empty() ? 0 : FileChecksums[i];
>       Builder.CreateCall(StartFile,
> 
> Added: llvm/trunk/test/Transforms/GCOVProfiling/modules.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/GCOVProfiling/modules.ll?rev=258406&view=auto
> ==============================================================================
> --- llvm/trunk/test/Transforms/GCOVProfiling/modules.ll (added)
> +++ llvm/trunk/test/Transforms/GCOVProfiling/modules.ll Thu Jan 21 11:04:42 2016
> @@ -0,0 +1,12 @@
> +; RUN: opt -insert-gcov-profiling -o - < %s | llvm-dis | FileCheck -check-prefix=EMIT-ARCS %s
> +
> +; EMIT-ARCS-NOT: call void @llvm_gcda_start_file
> +
> +!llvm.dbg.cu = !{!0}
> +!llvm.module.flags = !{!3, !4}
> +
> +!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "LLVM", isOptimized: false, runtimeVersion: 2, splitDebugFilename: "my.dwo", emissionKind: 1, enums: !2, retainedTypes: !2, subprograms: !2, globals: !2, imports: !2, dwoId: 43981)
> +!1 = !DIFile(filename: "<stdin>", directory: "/")
> +!2 = !{}
> +!3 = !{i32 2, !"Dwarf Version", i32 4}
> +!4 = !{i32 2, !"Debug Info Version", i32 3}
> 
> 
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