[TargetLoweringObjectFileImpl] Make .llvmbc and .llvmcmd non-SHF_ALLOC

There are two ways .llvmbc can be produced:

* clang -c -fembed-bitcode=all (which also produces .llvmcmd)
* LTO backend: ld.lld -mllvm -lto-embed-bitcode or -plugin-opt=-lto-embed-bitcode

.llvmbc and .llvmcmd have the SHF_ALLOC flag, so they can be dropped by
--gc-sections.

This patch sets SectionKind::Metadata to drop the SHF_ALLOC flag. This
is conceptually correct: the two sections are not part of the process
image, so SHF_ALLOC is not appropriate.

`test/LTO/X86/embed-bitcode.ll`: changed `llvm-objcopy -O binary --only-section` to
`llvm-objcopy --dump-section`. `-O binary` does not dump non-SHF_ALLOC sections.

Reviewed By: tejohnson

Differential Revision: https://reviews.llvm.org/D86374

1 files changed, 2 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
index 4c3e6cc..c2ea5d9 100644
--- a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
+++ b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
@@ -436,7 +436,8 @@ static SectionKind getELFKindForNamedSection(StringRef Name, SectionKind K) {
   if (Name == getInstrProfSectionName(IPSK_covmap, Triple::ELF,
                                       /*AddSegmentInfo=*/false) ||
       Name == getInstrProfSectionName(IPSK_covfun, Triple::ELF,
-                                      /*AddSegmentInfo=*/false))
+                                      /*AddSegmentInfo=*/false) ||
+      Name == ".llvmbc" || Name == ".llvmcmd")
     return SectionKind::getMetadata();
 
   if (Name.empty() || Name[0] != '.') return K;