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[ThinLTO] Make -lto-embed-bitcode an enum

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The current behavior of -lto-embed-bitcode is not quite the same as that
of -fembed-bitcode. While both populate .llvmbc with bitcode, the latter
populates it with pre-optimized bitcode(*), while the former with
post-optimized. The scenarios driving them are different - the latter's
goal is to allow re-compilation, while the former, IIUC, is execution.

I plan to add a third mode for thinlto cases, closely-related to
-fembed-bitcode's scenario: adding the bitcode pre-optimization, but
post-merging. This would allow re-compilation without requiring the
other .bc files that were merged (akin to how -fembed-bitcode allows
recompilation without all the .h files)

The third mode can't co-exist with the current -lto-embed-bitcode mode,
because the latter would overwrite it. For clarity, we change
-lto-embed-bitcode to be an enum.

(*) That's the compiler semantics. The driver splits compilation in 2
phases, so if -fembed-bitcode is given to the driver, the .llvmbc is
optimized bitcode; if the option is passed to the compiler (after -cc1),
the section is pre-optimized.

Differential Revision: https://reviews.llvm.org/D87477
This commit is contained in:
Mircea Trofin 2020-09-10 12:16:26 -07:00
parent 4522227204
commit a6aa03251f
2 changed files with 19 additions and 14 deletions
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29
lib/LTO/LTOBackend.cpp
View File

@ -50,6 +50,19 @@
using namespace llvm;
using namespace lto;
enum class LTOBitcodeEmbedding {
DoNotEmbed = 0,
EmbedOptimized = 1,
};
static cl::opt<LTOBitcodeEmbedding> EmbedBitcode(
"lto-embed-bitcode", cl::init(LTOBitcodeEmbedding::DoNotEmbed),
cl::values(clEnumValN(LTOBitcodeEmbedding::DoNotEmbed, "none",
"Do not embed"),
clEnumValN(LTOBitcodeEmbedding::EmbedOptimized, "optimized",
"Embed after all optimization passes")),
cl::desc("Embed LLVM bitcode in object files produced by LTO"));
LLVM_ATTRIBUTE_NORETURN static void reportOpenError(StringRef Path, Twine Msg) {
errs() << "failed to open " << Path << ": " << Msg << '\n';
errs().flush();
@ -346,24 +359,16 @@ bool opt(const Config &Conf, TargetMachine *TM, unsigned Task, Module &Mod,
return !Conf.PostOptModuleHook || Conf.PostOptModuleHook(Task, Mod);
}
static cl::opt<bool> EmbedBitcode(
"lto-embed-bitcode", cl::init(false),
cl::desc("Embed LLVM bitcode in object files produced by LTO"));
static void EmitBitcodeSection(Module &M) {
if (!EmbedBitcode)
return;
llvm::EmbedBitcodeInModule(M, llvm::MemoryBufferRef(), /*EmbedBitcode*/ true,
/*EmbedMarker*/ false, /*CmdArgs*/ nullptr);
}
void codegen(const Config &Conf, TargetMachine *TM, AddStreamFn AddStream,
unsigned Task, Module &Mod,
const ModuleSummaryIndex &CombinedIndex) {
if (Conf.PreCodeGenModuleHook && !Conf.PreCodeGenModuleHook(Task, Mod))
return;
EmitBitcodeSection(Mod);
if (EmbedBitcode == LTOBitcodeEmbedding::EmbedOptimized)
llvm::EmbedBitcodeInModule(Mod, llvm::MemoryBufferRef(),
/*EmbedBitcode*/ true,
/*EmbedMarker*/ false, /*CmdArgs*/ nullptr);
std::unique_ptr<ToolOutputFile> DwoOut;
SmallString<1024> DwoFile(Conf.SplitDwarfOutput);

4
test/LTO/X86/embed-bitcode.ll
View File

@ -5,10 +5,10 @@
; RUN: llvm-lto2 run -r %t1.o,_start,px -r %t2.o,foo,px -r %t3.o,bar,px -r %t2.o,bar,lx -o %t3 %t1.o %t2.o %t3.o
; RUN: llvm-readelf -S %t3.0 | FileCheck %s --implicit-check-not=.llvmbc
; RUN: llvm-lto2 run -r %t1.o,_start,px -r %t2.o,foo,px -r %t3.o,bar,px -r %t2.o,bar,lx -lto-embed-bitcode=false -o %t3 %t1.o %t2.o %t3.o
; RUN: llvm-lto2 run -r %t1.o,_start,px -r %t2.o,foo,px -r %t3.o,bar,px -r %t2.o,bar,lx -lto-embed-bitcode=none -o %t3 %t1.o %t2.o %t3.o
; RUN: llvm-readelf -S %t3.0 | FileCheck %s --implicit-check-not=.llvmbc
; RUN: llvm-lto2 run -r %t1.o,_start,px -r %t2.o,foo,px -r %t3.o,bar,px -r %t2.o,bar,lx -lto-embed-bitcode -o %t3 %t1.o %t2.o %t3.o
; RUN: llvm-lto2 run -r %t1.o,_start,px -r %t2.o,foo,px -r %t3.o,bar,px -r %t2.o,bar,lx -lto-embed-bitcode=optimized -o %t3 %t1.o %t2.o %t3.o
; RUN: llvm-readelf -S %t3.0 | FileCheck %s --check-prefix=CHECK-ELF
; RUN: llvm-objcopy --dump-section=.llvmbc=%t-embedded.bc %t3.0 /dev/null
; RUN: llvm-dis %t-embedded.bc -o - | FileCheck %s --check-prefix=CHECK-LL