[LTO][lld] Add lto-pgo-warn-mismatch option

[YolandaCY]

Summary

When enable CSPGO for ThinLTO, there are profile cfg mismatch warnings that will cause lld-link errors (with /WX)
due to source changes (e.g. #if code runs for profile generation but not for profile use)
To disable it we have to use an internal "/mllvm:-no-pgo-warn-mismatch" option.
In contrast clang uses option ”-Wno-backend-plugin“ to avoid such warnings and gcc has an explicit "-Wno-coverage-mismatch" option.

Add "lto-pgo-warn-mismatch" option to lld COFF/ELF to help turn on/off the profile mismatch warnings explicitly when build with ThinLTO and CSPGO.

[YolandaCY]

Fix default value in config and update the comment message

[YolandaCY]

Reset previous commit

[wenlei]

+ @xur

[YolandaCY]

Fix default config value and option description

[YolandaCY]

reset previous commit.

[YolandaCY]

fix lto config default value and update option description

[YolandaCY]

Could you help take a look?

[YolandaCY]

+ @pengfei

[tejohnson]

Does the same issue exist on ELF?

@xur can you take a look - are these mismatches expected?

@YolandaCY could you just pass through the internal option? Not familiar with COFF syntax by for ELF with lld this is -Wl,-mllvm,-no-pgo-warn-mismatch. I assume COFF has a similar mechanism.

[xur]

CSPGO can have mismatches -- it's just like PGO that is triggered by a source change, or a compiler change (before the pass).
Usually if there is a mismatch, PGO use pass will catch it first. There are cases that PGO has no-mismatch while CSPGO has a mismatch, but I consider it extremely rare.

Did you see the same warning in PGO?

As Teresa mentioned, I think the internal option should also work. But I do see the point of setting the argument in Conf to avoid the use of internal option.

[YolandaCY]

@tejohnson Yes, I think the same issue exists for ELF. I just submit this for COFF to make sure the general process works, and may submit a seperate patch for ELF if necessary.
I verified the -mllvm or /mllvm option works for both COFF and ELF. Thank you for the suggestion!

@xur The mismatch happens for both PGO and CSPGO in my case. The PGO pass may catch it firstly when compile to object files, and then CSPGO will catch it again during post-link ThinLTO. We have root-caused that some of these mismatches are due to some specialization code when generate the profiles but disabled later for profile use.
Please find discussions on these warnings in Chromium bug: https://bugs.chromium.org/p/chromium/issues/detail?id=978401

Do you think we still need an explicit linker option to turn off the warnings (actually errors for lld link)?

[tejohnson]

A few high level comments/questions based on the discussion:

• Is there a clang option? I thought there was but can't find one now. We should probably take the same approach here for the linker (external option vs use of the internal llvm option, similar name).
• Since this is affecting regular PGO mismatches (via NoPGOWarnMismatch) and not just CSPGO the name should presumably not mention the "CS" part.
• Please add for ELF as well in the same patch - should be straightfoward.
• Tests needed.

We should probably settle the first question above first though - i.e. is there a clang driver option and if not, perhaps the internal option should be used via the linker as well.

[YolandaCY]

Thanks Teresa for the comments.

For the first question, clang uses the -Wno-backend-plugin option to ignore the warnings.
This is mentioned in the How to build clang and LLVM with PGO user guide.

I haven't figured out how this correlates to the internal -no-pgo-warn-mismatch option though. Any tips?

[tejohnson]

In D104431#2835530, @YolandaCY wrote:

Thanks Teresa for the comments.

For the first question, clang uses the -Wno-backend-plugin option to ignore the warnings.
This is mentioned in the How to build clang and LLVM with PGO user guide.

I haven't figured out how this correlates to the internal -no-pgo-warn-mismatch option though. Any tips?

I traced it through and it looks like it will disable any warning coming from outside of clang (so LLVM) that doesn't have another type of handling in this switch statement:
http://llvm-cs.pcc.me.uk/tools/clang/lib/CodeGen/CodeGenAction.cpp#818

So it looks like a larger hammer because it could affect other warning types too.

@xur @davidxl do either of you know why we don't support something more fine grained in clang such as gcc's -Wno-coverage-mismatch?

[YolandaCY]

In D104431#2836028, @tejohnson wrote:

In D104431#2835530, @YolandaCY wrote:

Thanks Teresa for the comments.

For the first question, clang uses the -Wno-backend-plugin option to ignore the warnings.
This is mentioned in the How to build clang and LLVM with PGO user guide.

I haven't figured out how this correlates to the internal -no-pgo-warn-mismatch option though. Any tips?

I traced it through and it looks like it will disable any warning coming from outside of clang (so LLVM) that doesn't have another type of handling in this switch statement:
http://llvm-cs.pcc.me.uk/tools/clang/lib/CodeGen/CodeGenAction.cpp#818

So it looks like a larger hammer because it could affect other warning types too.

@xur @davidxl do either of you know why we don't support something more fine grained in clang such as gcc's -Wno-coverage-mismatch?

Thanks Teresa for the pointer.

The corresponding lld diagnostic handler can be found at:
http://llvm-cs.pcc.me.uk/tools/lld/Common/ErrorHandler.cpp#66
It is much simpler and does not distingush the kind. And it is initialized in the LTOLLVMContext:
http://llvm-cs.pcc.me.uk/include/llvm/LTO/Config.h#228

It seems that to add a similar option as clang we may need to add an lto specific DiagnosticHandlerFunction (not share lld's) and check for all diagnostic kinds as clang?
Or shall we just add a fine grained option similar to gcc?

[tejohnson]

In D104431#2843631, @YolandaCY wrote:

In D104431#2836028, @tejohnson wrote:

In D104431#2835530, @YolandaCY wrote:

Thanks Teresa for the comments.

For the first question, clang uses the -Wno-backend-plugin option to ignore the warnings.
This is mentioned in the How to build clang and LLVM with PGO user guide.

I haven't figured out how this correlates to the internal -no-pgo-warn-mismatch option though. Any tips?

I traced it through and it looks like it will disable any warning coming from outside of clang (so LLVM) that doesn't have another type of handling in this switch statement:
http://llvm-cs.pcc.me.uk/tools/clang/lib/CodeGen/CodeGenAction.cpp#818

So it looks like a larger hammer because it could affect other warning types too.

@xur @davidxl do either of you know why we don't support something more fine grained in clang such as gcc's -Wno-coverage-mismatch?

Thanks Teresa for the pointer.

The corresponding lld diagnostic handler can be found at:
http://llvm-cs.pcc.me.uk/tools/lld/Common/ErrorHandler.cpp#66
It is much simpler and does not distingush the kind. And it is initialized in the LTOLLVMContext:
http://llvm-cs.pcc.me.uk/include/llvm/LTO/Config.h#228

It seems that to add a similar option as clang we may need to add an lto specific DiagnosticHandlerFunction (not share lld's) and check for all diagnostic kinds as clang?
Or shall we just add a fine grained option similar to gcc?

Personally I find it reasonable to have a way to disable just these warnings. I do find it unfortunate that the support for disabling these warnings is and will still be at a different granularity in clang vs LTO.

@xur @davidxl ping on history for not supporting a finer grain option for disabling this warning via clang.

My feeling is that it would be fine to go ahead here but I'd prefer that you add support for the ELF side as well.

[YolandaCY]

Add ELF support and tests

[YolandaCY]

In D104431#2856258, @tejohnson wrote:

Personally I find it reasonable to have a way to disable just these warnings. I do find it unfortunate that the support for disabling these warnings is and will still be at a different granularity in clang vs LTO.

@xur @davidxl ping on history for not supporting a finer grain option for disabling this warning via clang.

My feeling is that it would be fine to go ahead here but I'd prefer that you add support for the ELF side as well.

Thank you Teresa for the suggestions. I have added the option for ELF and also some tests. Please help take a look.

[tejohnson]

lgtm with a test fix noted below.

lld/test/COFF/thinlto-pgo-warn.ll

11 ↗

(On Diff #357691)

I think it would be cleaner to do a FileCheck --implicit-check-not warning (possibly with an --allow-empty to get FileCheck to succeed). I don't think it is is typical to test for the absence of a pattern by checking for a FileCheck failure.

Ditto for ELF test.

[MaskRay]

lld/test/ELF/lto/thinlto-pgo-warn.ll

3 ↗

(On Diff #357691)

Newer lld/test/ELF tests use ;; for non-RUN-non-CHECK comments.

8 ↗

(On Diff #357691)

Drop --plugin-opt=thinlto

--lto-O2

11 ↗

(On Diff #357691)

ditto

[YolandaCY]

update tests

[YolandaCY]

Thanks Teresa and Fangrui for the comments. I have revised the tests as suggested!

lld/test/COFF/thinlto-pgo-warn.ll

11 ↗

(On Diff #357691)

Thank you Teresa for the hint. I have updated the negative test as suggested.

lld/test/ELF/lto/thinlto-pgo-warn.ll

3 ↗

(On Diff #357691)

Thanks and updated the comments for ELF test with "::".

[MaskRay]

lld/test/COFF/thinlto-pgo-warn.ll

11 ↗

(On Diff #357691)

https://llvm.org/docs/CommandGuide/FileCheck.html

--implicit-check-not warning:

lld/test/ELF/lto/thinlto-pgo-warn.ll

11 ↗

(On Diff #361956)

ditto

[YolandaCY]

Amend negative check

[YolandaCY]

lld/test/COFF/thinlto-pgo-warn.ll

11 ↗

(On Diff #357691)

Thank you @MaskRay for the reference. It seems I cannot use a check prefix as a check pattern.

I did not use "--implicit-check-no warning" directly as it looks to me a more strict test that negates all warnings.
In this case, would it be better to simply use CHECK-NOT ?
I checked that if I run with flag /lto-pgo-warn-mismatch without the CHECK-WARNING prefix, FILECHECK will catch the failure.

[YolandaCY]

rebase

[YolandaCY]

Update test as warning message changed after rebase

[c-rhodes]

Hi, this is breaking my build:

[1860/2777] Linking CXX shared library lib/libLLVMLTO.so.14git
FAILED: lib/libLLVMLTO.so.14git
: && /usr/bin/clang++-13 -fPIC -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -pedantic -Wno-long-long -Wc++98-compat-extra-semi -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wstring-conversion -fdiagnostics-color -g  -Wl,--gdb-index -Wl,-z,defs -Wl,-z,nodelete -fuse-ld=lld-13 -Wl,--color-diagnostics -shared -Wl,-soname,libLLVMLTO.so.14git -o lib/libLLVMLTO.so.14git lib/LTO/CMakeFiles/LLVMLTO.dir/Caching.cpp.o lib/LTO/CMakeFiles/LLVMLTO.dir/LTO.cpp.o lib/LTO/CMakeFiles/LLVMLTO.dir/LTOBackend.cpp.o lib/LTO/CMakeFiles/LLVMLTO.dir/LTOModule.cpp.o lib/LTO/CMakeFiles/LLVMLTO.dir/LTOCodeGenerator.cpp.o lib/LTO/CMakeFiles/LLVMLTO.dir/SummaryBasedOptimizations.cpp.o lib/LTO/CMakeFiles/LLVMLTO.dir/UpdateCompilerUsed.cpp.o lib/LTO/CMakeFiles/LLVMLTO.dir/ThinLTOCodeGenerator.cpp.o  -Wl,-rpath,"\$ORIGIN/../lib"  lib/libLLVMCodeGen.so.14git  lib/libLLVMExtensions.so.14git  lib/libLLVMPasses.so.14git  lib/libLLVMTarget.so.14git  lib/libLLVMObjCARCOpts.so.14git  lib/libLLVMipo.so.14git  lib/libLLVMBitWriter.so.14git  lib/libLLVMLinker.so.14git  lib/libLLVMScalarOpts.so.14git  lib/libLLVMAggressiveInstCombine.so.14git  lib/libLLVMInstCombine.so.14git  lib/libLLVMTransformUtils.so.14git  lib/libLLVMAnalysis.so.14git  lib/libLLVMObject.so.14git  lib/libLLVMBitReader.so.14git  lib/libLLVMMC.so.14git  lib/libLLVMCore.so.14git  lib/libLLVMBinaryFormat.so.14git  lib/libLLVMRemarks.so.14git  lib/libLLVMSupport.so.14git  -Wl,-rpath-link,/home/culrho01/llvm-project/build/lib && :
ld.lld-13: error: undefined symbol: NoPGOWarnMismatch
>>> referenced by LTOBackend.cpp:228 (/home/culrho01/llvm-project/llvm/lib/LTO/LTOBackend.cpp:228)
>>>               lib/LTO/CMakeFiles/LLVMLTO.dir/LTOBackend.cpp.o:(runNewPMPasses(llvm::lto::Config const&, llvm::Module&, llvm::TargetMachine*, unsigned int, bool, llvm::ModuleSummaryIndex*, llvm::ModuleSummaryIndex const*))
clang: error: linker command failed with exit code 1 (use -v to see invocation)

[YolandaCY]

I seems cannot reproduce the failure. I tried:

cmake -DLLVM_ENABLE_PROJECTS=mlir -DLLVM_ENABLE_ASSERTIONS=On -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=/opt/llvm/ -DLLVM_TARGETS_TO_BUILD=X86;NVPTX;AMDGPU -DLLVM_BUILD_EXAMPLES=ON -G Ninja ../llvm

ninja -j10

Is it specific to mlir build?

In D104431#2938948, @c-rhodes wrote:

Hi, this is breaking my build:

[1860/2777] Linking CXX shared library lib/libLLVMLTO.so.14git
FAILED: lib/libLLVMLTO.so.14git
: && /usr/bin/clang++-13 -fPIC -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -pedantic -Wno-long-long -Wc++98-compat-extra-semi -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wstring-conversion -fdiagnostics-color -g  -Wl,--gdb-index -Wl,-z,defs -Wl,-z,nodelete -fuse-ld=lld-13 -Wl,--color-diagnostics -shared -Wl,-soname,libLLVMLTO.so.14git -o lib/libLLVMLTO.so.14git lib/LTO/CMakeFiles/LLVMLTO.dir/Caching.cpp.o lib/LTO/CMakeFiles/LLVMLTO.dir/LTO.cpp.o lib/LTO/CMakeFiles/LLVMLTO.dir/LTOBackend.cpp.o lib/LTO/CMakeFiles/LLVMLTO.dir/LTOModule.cpp.o lib/LTO/CMakeFiles/LLVMLTO.dir/LTOCodeGenerator.cpp.o lib/LTO/CMakeFiles/LLVMLTO.dir/SummaryBasedOptimizations.cpp.o lib/LTO/CMakeFiles/LLVMLTO.dir/UpdateCompilerUsed.cpp.o lib/LTO/CMakeFiles/LLVMLTO.dir/ThinLTOCodeGenerator.cpp.o  -Wl,-rpath,"\$ORIGIN/../lib"  lib/libLLVMCodeGen.so.14git  lib/libLLVMExtensions.so.14git  lib/libLLVMPasses.so.14git  lib/libLLVMTarget.so.14git  lib/libLLVMObjCARCOpts.so.14git  lib/libLLVMipo.so.14git  lib/libLLVMBitWriter.so.14git  lib/libLLVMLinker.so.14git  lib/libLLVMScalarOpts.so.14git  lib/libLLVMAggressiveInstCombine.so.14git  lib/libLLVMInstCombine.so.14git  lib/libLLVMTransformUtils.so.14git  lib/libLLVMAnalysis.so.14git  lib/libLLVMObject.so.14git  lib/libLLVMBitReader.so.14git  lib/libLLVMMC.so.14git  lib/libLLVMCore.so.14git  lib/libLLVMBinaryFormat.so.14git  lib/libLLVMRemarks.so.14git  lib/libLLVMSupport.so.14git  -Wl,-rpath-link,/home/culrho01/llvm-project/build/lib && :
ld.lld-13: error: undefined symbol: NoPGOWarnMismatch
>>> referenced by LTOBackend.cpp:228 (/home/culrho01/llvm-project/llvm/lib/LTO/LTOBackend.cpp:228)
>>>               lib/LTO/CMakeFiles/LLVMLTO.dir/LTOBackend.cpp.o:(runNewPMPasses(llvm::lto::Config const&, llvm::Module&, llvm::TargetMachine*, unsigned int, bool, llvm::ModuleSummaryIndex*, llvm::ModuleSummaryIndex const*))
clang: error: linker command failed with exit code 1 (use -v to see invocation)

[pengfei]

Thanks @c-rhodes for reporting this. I have reverted it.

[c-rhodes]

In D104431#2938959, @YolandaCY wrote:

I seems cannot reproduce the failure. I tried:

cmake -DLLVM_ENABLE_PROJECTS=mlir -DLLVM_ENABLE_ASSERTIONS=On -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=/opt/llvm/ -DLLVM_TARGETS_TO_BUILD=X86;NVPTX;AMDGPU -DLLVM_BUILD_EXAMPLES=ON -G Ninja ../llvm

ninja -j10

Is it specific to mlir build?

I'm not building MLIR, here's my cmake line if it helps: cmake -G Ninja -DCMAKE_C_COMPILER=clang-13 -DCMAKE_CXX_COMPILER=clang++-13 -DCMAKE_EXE_LINKER_FLAGS="-Wl,--gdb-index" -DCMAKE_SHARED_LINKER_FLAGS="-Wl,--gdb-index" -DCMAKE_MODULE_LINKER_FLAGS="-Wl,--gdb-index" -DLLVM_USE_LINKER=lld-13 -DLLVM_USE_SPLIT_DWARF=OFF -DLLVM_APPEND_VC_REV=OFF -DLLVM_CCACHE_BUILD=ON -DBUILD_SHARED_LIBS=ON -DCMAKE_BUILD_TYPE=Debug '-DLLVM_ENABLE_PROJECTS=llvm;clang' -DCMAKE_INSTALL_PREFIX=install -DLLVM_TARGETS_TO_BUILD="X86;AArch64;RISCV" ../llvm

[pengfei]

@YolandaCY, Did you test the shared build with -DBUILD_SHARED_LIBS=ON ? Is it because NoPGOWarnMismatch is defined in PGO while used in LTO?

[YolandaCY]

In D104431#2938966, @pengfei wrote:

@YolandaCY, Did you test the shared build with -DBUILD_SHARED_LIBS=ON ? Is it because NoPGOWarnMismatch is defined in PGO while used in LTO?

Yes, I guess so. I did not use -DBUILD_SHARED_LIBS=ON yet. I will have a try. Thank you all for hints!

[zsrkmyn]

I met the same issue. It may be fixed by the following patch.

diff --git a/llvm/lib/LTO/CMakeLists.txt b/llvm/lib/LTO/CMakeLists.txt
index e6adfd43e7f9..bbe256b3327b 100644
--- a/llvm/lib/LTO/CMakeLists.txt
+++ b/llvm/lib/LTO/CMakeLists.txt
@@ -25,6 +25,7 @@ add_llvm_component_library(LLVMLTO
   Extensions
   IPO
   InstCombine
+  LLVMInstrumentation
   Linker
   MC
   ObjCARC

[MaskRay]

fix build. fix cl::opt namespace

[MaskRay]

lld/test/ELF/lto/thinlto-pgo-warn.ll

8 ↗

(On Diff #365672)

No need to use 1/2/3 suffixes for different stages of the same source file.

13 ↗

(On Diff #365672)

The exact hash value isn't necessary. It will just add maintenance burden when this changes.

[MaskRay]

rename tests and simplify

[rnk]

lld/test/COFF/pgo-warn-mismatch.ll

5

This is the first use of llvm-profdata in the lld test suite, and it is not already a declared dependency for the test suite. I will add it in a moment. Without declaring test dependencies, the test may fail if one simply runs "check-lld" in a fresh build directory.

lld/COFF/Config.h

struct Configuration {
   llvm::StringRef ltoObjPath;
 
   // Used for /lto-cs-profile-generate:
   bool ltoCSProfileGenerate = false;
 
   // Used for /lto-cs-profile-path
   llvm::StringRef ltoCSProfileFile;
 
+  // Used for /lto-pgo-warn-mismatch:
+  bool ltoPGOWarnMismatch = true;
+
   // Used for /call-graph-ordering-file:
   llvm::MapVector<std::pair<const SectionChunk *, const SectionChunk *>,
                   uint64_t>
       callGraphProfile;
   bool callGraphProfileSort = false;
 
   // Used for /print-symbol-order:
   StringRef printSymbolOrder;

lld/COFF/Driver.cpp

void LinkerDriver::linkerMain(ArrayRef<const char *> argsArr) {
   config->thinLTOPrefixReplace =
       getOldNewOptions(args, OPT_thinlto_prefix_replace);
   config->thinLTOObjectSuffixReplace =
       getOldNewOptions(args, OPT_thinlto_object_suffix_replace);
   config->ltoObjPath = args.getLastArgValue(OPT_lto_obj_path);
   config->ltoCSProfileGenerate = args.hasArg(OPT_lto_cs_profile_generate);
   config->ltoCSProfileFile = args.getLastArgValue(OPT_lto_cs_profile_file);
   // Handle miscellaneous boolean flags.
+  config->ltoPGOWarnMismatch = args.hasFlag(OPT_lto_pgo_warn_mismatch,
+                                            OPT_lto_pgo_warn_mismatch_no, true);
   config->allowBind = args.hasFlag(OPT_allowbind, OPT_allowbind_no, true);
   config->allowIsolation =
       args.hasFlag(OPT_allowisolation, OPT_allowisolation_no, true);
   config->incremental =
       args.hasFlag(OPT_incremental, OPT_incremental_no,
                    !config->doGC && config->doICF == ICFLevel::None &&
                        !args.hasArg(OPT_order) && !args.hasArg(OPT_profile));
   config->integrityCheck =

lld/COFF/LTO.cpp

static lto::Config createConfig() {
   c.CPU = getCPUStr();
   c.MAttrs = getMAttrs();
   c.CGOptLevel = args::getCGOptLevel(config->ltoo);
   c.AlwaysEmitRegularLTOObj = !config->ltoObjPath.empty();
   c.UseNewPM = config->ltoNewPassManager;
   c.DebugPassManager = config->ltoDebugPassManager;
   c.CSIRProfile = std::string(config->ltoCSProfileFile);
   c.RunCSIRInstr = config->ltoCSProfileGenerate;
+  c.PGOWarnMismatch = config->ltoPGOWarnMismatch;
 
   if (config->saveTemps)
     checkError(c.addSaveTemps(std::string(config->outputFile) + ".",
                               /*UseInputModulePath*/ true));
   return c;
 }
 
 BitcodeCompiler::BitcodeCompiler() {

lld/COFF/Options.td

def thinlto_prefix_replace: P<
     "'old;new' replace old prefix with new prefix in ThinLTO outputs">;
 def lto_obj_path : P<
     "lto-obj-path",
     "output native object for merged LTO unit to this path">;
 def lto_cs_profile_generate: F<"lto-cs-profile-generate">,
     HelpText<"Perform context sensitive PGO instrumentation">;
 def lto_cs_profile_file : P<"lto-cs-profile-file",
     "Context sensitive profile file path">;
+defm lto_pgo_warn_mismatch: B<
+     "lto-pgo-warn-mismatch",
+     "turn on warnings about profile cfg mismatch (default)>",
+     "turn off warnings about profile cfg mismatch">;
 def dash_dash_version : Flag<["--"], "version">,
   HelpText<"Display the version number and exit">;
 def threads
     : P<"threads", "Number of threads. '1' disables multi-threading. By "
                    "default all available hardware threads are used">;
 def call_graph_ordering_file: P<
     "call-graph-ordering-file", 
     "Layout sections to optimize the given callgraph">;

lld/ELF/Config.h

struct Configuration {
   bool gcSections;
   bool gdbIndex;
   bool gnuHash = false;
   bool gnuUnique;
   bool hasDynSymTab;
   bool ignoreDataAddressEquality;
   bool ignoreFunctionAddressEquality;
   bool ltoCSProfileGenerate;
+  bool ltoPGOWarnMismatch;
   bool ltoDebugPassManager;
   bool ltoEmitAsm;
   bool ltoNewPassManager;
   bool ltoPseudoProbeForProfiling;
   bool ltoUniqueBasicBlockSectionNames;
   bool ltoWholeProgramVisibility;
   bool mergeArmExidx;
   bool mipsN32Abi = false;

lld/ELF/Driver.cpp

static void readConfigs(opt::InputArgList &args) {
   config->ignoreDataAddressEquality =
       args.hasArg(OPT_ignore_data_address_equality);
   config->ignoreFunctionAddressEquality =
       args.hasArg(OPT_ignore_function_address_equality);
   config->init = args.getLastArgValue(OPT_init, "_init");
   config->ltoAAPipeline = args.getLastArgValue(OPT_lto_aa_pipeline);
   config->ltoCSProfileGenerate = args.hasArg(OPT_lto_cs_profile_generate);
   config->ltoCSProfileFile = args.getLastArgValue(OPT_lto_cs_profile_file);
+  config->ltoPGOWarnMismatch = args.hasFlag(OPT_lto_pgo_warn_mismatch,
+                                            OPT_no_lto_pgo_warn_mismatch, true);
   config->ltoDebugPassManager = args.hasArg(OPT_lto_debug_pass_manager);
   config->ltoEmitAsm = args.hasArg(OPT_lto_emit_asm);
   config->ltoNewPassManager =
       args.hasFlag(OPT_no_lto_legacy_pass_manager, OPT_lto_legacy_pass_manager,
                    LLVM_ENABLE_NEW_PASS_MANAGER);
   config->ltoNewPmPasses = args.getLastArgValue(OPT_lto_newpm_passes);
   config->ltoWholeProgramVisibility =
       args.hasFlag(OPT_lto_whole_program_visibility,

lld/ELF/LTO.cpp

static lto::Config createConfig() {
   for (const llvm::StringRef &name : config->thinLTOModulesToCompile)
     c.ThinLTOModulesToCompile.emplace_back(name);
 
   c.TimeTraceEnabled = config->timeTraceEnabled;
   c.TimeTraceGranularity = config->timeTraceGranularity;
 
   c.CSIRProfile = std::string(config->ltoCSProfileFile);
   c.RunCSIRInstr = config->ltoCSProfileGenerate;
+  c.PGOWarnMismatch = config->ltoPGOWarnMismatch;
 
   if (config->emitLLVM) {
     c.PostInternalizeModuleHook = [](size_t task, const Module &m) {
       if (std::unique_ptr<raw_fd_ostream> os =
               openLTOOutputFile(config->outputFile))
         WriteBitcodeToFile(m, *os, false);
       return false;
     };

lld/ELF/Options.td

 def lto_O: JJ<"lto-O">, MetaVarName<"<opt-level>">,
   HelpText<"Optimization level for LTO">;
 def lto_partitions: JJ<"lto-partitions=">,
   HelpText<"Number of LTO codegen partitions">;
 def lto_cs_profile_generate: FF<"lto-cs-profile-generate">,
   HelpText<"Perform context sensitive PGO instrumentation">;
 def lto_cs_profile_file: JJ<"lto-cs-profile-file=">,
   HelpText<"Context sensitive profile file path">;
+defm lto_pgo_warn_mismatch: BB<"lto-pgo-warn-mismatch",
+  "turn on warnings about profile cfg mismatch (default)>",
+  "turn off warnings about profile cfg mismatch">;
 def lto_obj_path_eq: JJ<"lto-obj-path=">;
 def lto_sample_profile: JJ<"lto-sample-profile=">,
   HelpText<"Sample profile file path">;
 defm lto_whole_program_visibility: BB<"lto-whole-program-visibility",
   "Asserts that the LTO link has whole program visibility",
   "Asserts that the LTO link does not have whole program visibility">;
 def lto_pseudo_probe_for_profiling: F<"lto-pseudo-probe-for-profiling">,
   HelpText<"Emit pseudo probes for sample profiling">;

lld/test/COFF/pgo-warn-mismatch.ll

+; REQUIRES: x86
+
+; RUN: rm -rf %t && split-file %s %t
+; RUN: opt -module-summary %t/a.ll -o %t/a.bc
+; RUN: llvm-profdata merge %t/cs.proftext -o %t/cs.profdata
+
+; Ensure lld generates warnings for profile cfg mismatch.
+; RUN: lld-link /dll /noentry /export:f /lto-cs-profile-file:%t/cs.profdata /lto-pgo-warn-mismatch /opt:lldlto=2 %t/a.bc /out:%t/a.dll 2>&1 | FileCheck %s
+
+; Ensure lld will not generate warnings for profile cfg mismatch.
+; RUN: lld-link /dll /noentry /export:f /lto-cs-profile-file:%t/cs.profdata /lto-pgo-warn-mismatch:no /opt:lldlto=2 %t/a.bc /out:%t/a.dll 2>&1 | count 0
+
+; CHECK: warning: {{.*}} function control flow change detected (hash mismatch) f Hash = [[#]]
+
+;--- a.ll
+target datalayout = "e-m:w-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-windows-msvc"
+
+define i32 @f(i32 returned %a) #0 {
+entry:
+  ret i32 %a
+}
+
+attributes #0 = { "target-cpu"="x86-64" }
+
+!llvm.module.flags = !{!0, !1}
+
+!0 = !{i32 1, !"wchar_size", i32 4}
+!1 = !{i32 1, !"ProfileSummary", !2}
+!2 = !{!3, !4, !5, !6, !7, !8, !9, !10, !11, !12}
+!3 = !{!"ProfileFormat", !"InstrProf"}
+!4 = !{!"TotalCount", i64 2}
+!5 = !{!"MaxCount", i64 1}
+!6 = !{!"MaxInternalCount", i64 0}
+!7 = !{!"MaxFunctionCount", i64 1}
+!8 = !{!"NumCounts", i64 3}
+!9 = !{!"NumFunctions", i64 2}
+!10 = !{!"IsPartialProfile", i64 0}
+!11 = !{!"PartialProfileRatio", double 0.000000e+00}
+!12 = !{!"DetailedSummary", !13}
+!13 = !{!14, !15, !16, !17, !18, !19, !20, !21, !22, !23, !24, !25, !26, !27, !28, !29}
+!14 = !{i32 10000, i64 0, i32 0}
+!15 = !{i32 100000, i64 0, i32 0}
+!16 = !{i32 200000, i64 0, i32 0}
+!17 = !{i32 300000, i64 0, i32 0}
+!18 = !{i32 400000, i64 0, i32 0}
+!19 = !{i32 500000, i64 1, i32 2}
+!20 = !{i32 600000, i64 1, i32 2}
+!21 = !{i32 700000, i64 1, i32 2}
+!22 = !{i32 800000, i64 1, i32 2}
+!23 = !{i32 900000, i64 1, i32 2}
+!24 = !{i32 950000, i64 1, i32 2}
+!25 = !{i32 990000, i64 1, i32 2}
+!26 = !{i32 999000, i64 1, i32 2}
+!27 = !{i32 999900, i64 1, i32 2}
+!28 = !{i32 999990, i64 1, i32 2}
+!29 = !{i32 999999, i64 1, i32 2}
+
+;--- cs.proftext
+# CSIR level Instrumentation Flag
+:csir
+f
+# Func Hash:
+1535914979662757887
+# Num Counters:
+2
+# Counter Values:
+1
+0
+

lld/test/ELF/lto/pgo-warn-mismatch.ll

+; REQUIRES: x86
+
+; RUN: rm -rf %t && split-file %s %t
+; RUN: opt -module-summary %t/a.ll -o %t/a.bc
+; RUN: llvm-profdata merge %t/cs.proftext -o %t/cs.profdata
+
+;; Ensure lld generates warnings for profile cfg mismatch.
+; RUN: ld.lld --lto-cs-profile-file=%t/cs.profdata --lto-pgo-warn-mismatch -shared %t/a.bc -o /dev/null 2>&1 | FileCheck %s
+
+;; Ensure lld will not generate warnings for profile cfg mismatch.
+; RUN: ld.lld --lto-cs-profile-file=%t/cs.profdata --no-lto-pgo-warn-mismatch -shared --fatal-warnings %t/a.bc -o /dev/null
+
+; CHECK: warning: {{.*}} function control flow change detected (hash mismatch) f Hash = [[#]]
+
+;--- a.ll
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define i32 @f(i32 returned %a) #0 {
+entry:
+  ret i32 %a
+}
+
+attributes #0 = { "target-cpu"="x86-64" }
+
+!llvm.module.flags = !{!0, !1}
+
+!0 = !{i32 1, !"wchar_size", i32 4}
+!1 = !{i32 1, !"ProfileSummary", !2}
+!2 = !{!3, !4, !5, !6, !7, !8, !9, !10, !11, !12}
+!3 = !{!"ProfileFormat", !"InstrProf"}
+!4 = !{!"TotalCount", i64 2}
+!5 = !{!"MaxCount", i64 1}
+!6 = !{!"MaxInternalCount", i64 0}
+!7 = !{!"MaxFunctionCount", i64 1}
+!8 = !{!"NumCounts", i64 3}
+!9 = !{!"NumFunctions", i64 2}
+!10 = !{!"IsPartialProfile", i64 0}
+!11 = !{!"PartialProfileRatio", double 0.000000e+00}
+!12 = !{!"DetailedSummary", !13}
+!13 = !{!14, !15, !16, !17, !18, !19, !20, !21, !22, !23, !24, !25, !26, !27, !28, !29}
+!14 = !{i32 10000, i64 0, i32 0}
+!15 = !{i32 100000, i64 0, i32 0}
+!16 = !{i32 200000, i64 0, i32 0}
+!17 = !{i32 300000, i64 0, i32 0}
+!18 = !{i32 400000, i64 0, i32 0}
+!19 = !{i32 500000, i64 1, i32 2}
+!20 = !{i32 600000, i64 1, i32 2}
+!21 = !{i32 700000, i64 1, i32 2}
+!22 = !{i32 800000, i64 1, i32 2}
+!23 = !{i32 900000, i64 1, i32 2}
+!24 = !{i32 950000, i64 1, i32 2}
+!25 = !{i32 990000, i64 1, i32 2}
+!26 = !{i32 999000, i64 1, i32 2}
+!27 = !{i32 999900, i64 1, i32 2}
+!28 = !{i32 999990, i64 1, i32 2}
+!29 = !{i32 999999, i64 1, i32 2}
+
+;--- cs.proftext
+# CSIR level Instrumentation Flag
+:csir
+f
+# Func Hash:
+1535914979662757887
+# Num Counters:
+2
+# Counter Values:
+1
+0
+

llvm/include/llvm/LTO/Config.h

struct Config {
   bool Freestanding = false;
 
   /// Disable entirely the optimizer, including importing for ThinLTO
   bool CodeGenOnly = false;
 
   /// Run PGO context sensitive IR instrumentation.
   bool RunCSIRInstr = false;
 
+  /// Turn on/off the warning about a hash mismatch in the PGO profile data.
+  bool PGOWarnMismatch = true;
+
   /// Asserts whether we can assume whole program visibility during the LTO
   /// link.
   bool HasWholeProgramVisibility = false;
 
   /// Always emit a Regular LTO object even when it is empty because no Regular
   /// LTO modules were linked. This option is useful for some build system which
   /// want to know a priori all possible output files.
   bool AlwaysEmitRegularLTOObj = false;

llvm/lib/LTO/CMakeLists.txt

add_llvm_component_library(LLVMLTO
   BinaryFormat
   BitReader
   BitWriter
   CodeGen
   Core
   Extensions
   IPO
   InstCombine
+  Instrumentation
   Linker
   MC
   ObjCARC
   Object
   Passes
   Remarks
   Scalar
   Support
   Target
   TransformUtils
 )

llvm/lib/LTO/LTOBackend.cpp

cl::values(clEnumValN(LTOBitcodeEmbedding::DoNotEmbed, "none",
                           "Embed post merge, but before optimizations")),
     cl::desc("Embed LLVM bitcode in object files produced by LTO"));
 
 static cl::opt<bool> ThinLTOAssumeMerged(
     "thinlto-assume-merged", cl::init(false),
     cl::desc("Assume the input has already undergone ThinLTO function "
              "importing and the other pre-optimization pipeline changes."));
 
+namespace llvm {
+extern cl::opt<bool> NoPGOWarnMismatch;
+}
+
 [[noreturn]] static void reportOpenError(StringRef Path, Twine Msg) {
   errs() << "failed to open " << Path << ": " << Msg << '\n';
   errs().flush();
   exit(1);
 }
 
 Error Config::addSaveTemps(std::string OutputFileName,
                            bool UseInputModulePath) {
static void runNewPMPasses(const Config &Conf, Module &Mod, TargetMachine *TM,
   else if (Conf.RunCSIRInstr) {
     PGOOpt = PGOOptions("", Conf.CSIRProfile, Conf.ProfileRemapping,
                         PGOOptions::IRUse, PGOOptions::CSIRInstr,
                         Conf.AddFSDiscriminator);
   } else if (!Conf.CSIRProfile.empty()) {
     PGOOpt = PGOOptions(Conf.CSIRProfile, "", Conf.ProfileRemapping,
                         PGOOptions::IRUse, PGOOptions::CSIRUse,
                         Conf.AddFSDiscriminator);
+    NoPGOWarnMismatch = !Conf.PGOWarnMismatch;
   } else if (Conf.AddFSDiscriminator) {
     PGOOpt = PGOOptions("", "", "", PGOOptions::NoAction,
                         PGOOptions::NoCSAction, true);
   }
 
   LoopAnalysisManager LAM;
   FunctionAnalysisManager FAM;
   CGSCCAnalysisManager CGAM;

llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp

 // Command line option to enable/disable the warning about missing profile
 // information.
 static cl::opt<bool>
     PGOWarnMissing("pgo-warn-missing-function", cl::init(false), cl::Hidden,
                    cl::desc("Use this option to turn on/off "
                             "warnings about missing profile data for "
                             "functions."));
 
+namespace llvm {
 // Command line option to enable/disable the warning about a hash mismatch in
 // the profile data.
-static cl::opt<bool>
+cl::opt<bool>
     NoPGOWarnMismatch("no-pgo-warn-mismatch", cl::init(false), cl::Hidden,
                       cl::desc("Use this option to turn off/on "
                                "warnings about profile cfg mismatch."));
+} // namespace llvm
 
 // Command line option to enable/disable the warning about a hash mismatch in
 // the profile data for Comdat functions, which often turns out to be false
 // positive due to the pre-instrumentation inline.
 static cl::opt<bool>
     NoPGOWarnMismatchComdat("no-pgo-warn-mismatch-comdat", cl::init(true),
                             cl::Hidden,
                             cl::desc("The option is used to turn on/off "