rematerialization rollback logic #4
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This allows individual stages to make decisions after re-scheduling individual regions.
When scheduling must be reverted for a region, the current implementation re-orders non-debug instructions and debug instructions separately; the former in a first pass and the latter in a second pass handled by a generic machine scheduler helper whose state is tied to the current region being scheduled, in turns limiting the revert logic to only work on the active scheduling region. This makes the revert logic work in a single pass for all MIs, and removes the restriction that it works exclusively on the active scheduling region. The latter enables future use cases such as reverting scheduling of multiple regions at once. While the instruction order produced should be identical to what it was before, small changes in slot indices of re-scheduled MIs yield different RA decisions and significant test churn.
When the rematerialization stage fails to increase occupancy in all regions, the current implementation only reverts the effect of re-scheduling in regions in which the increased occupancy target could not be achieved. However, given that re-scheduling with a higher occupancy target puts more pressure on the scheduler to achieve lower maximum RP at the cost of potentially lower ILP as well, region schedules made with higher occupancy targets are generally less desirable if the whole function is not able to meet that target. Therefore, if at least one region cannot reach its target, it makes sense to revert re-scheduling in all affected regions to go back to a schedule that was made with a lower occupancy target. This implements such logic for the rematerialization stage, and adds a test to showcase that re-scheduling is indeed interrupted/reverted as soon as a re-scheduled region that does not meet the increased target occupancy is encountered. As a minor improvement, this also sets higher occupancy targets for re-scheduling at the end of stage initialization in some cases. In cases where rematerializations alone are not able to achieve the target, this can push the scheduler to be more aggressive in reducing RP and achieve the target.
…lvm#175050)" This re-applies commit f21e359 along with the compile fix failure introduced in 8ab7937 before the initial patch was reverted and fixes for the previously observed assert failure. We were hitting the assert in the HIP Blender due to a combination of two issues that could happen when rematerializations are being rolled back. 1. Small changes in slots indices (while preserving instruction order) compared to the pre-re-scheduling state meand that we have to re-compute live ranges for all register operands of rolled back rematerializations. This was not being done before. 2. Re-scheduling can move registers that were rematerialized at arbitrary positions in their respective regions while their opcode is set to DBG_VALUE, even before their read operands are defined. This makes re-scheduling reverts mandatory before rolling back rematerializations, as otherwise def-use chains may be broken. The original patch did not guatantee that, but previous refactoring of the rollback/revert logic for the rematerialization stage now ensures that reverts always precede rollbacks.
lucas-rami
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Jan 23, 2026
… all redeclarations (llvm#176188) Fix handling of `lifetimebound` attributes on implicit `this` parameters across function redeclarations. Previously, the lifetime analysis would miss `lifetimebound` attributes on implicit `this` parameters if they were only present on certain redeclarations of a method. This could lead to false negatives in the lifetime safety analysis. This change ensures that if any redeclaration of a method has the attribute, it will be properly detected and used in the analysis. I can't seem to work around the crash in the earlier attempt llvm#172146. Reproducer of the original crash: ```cpp struct a { a &b() [[_Clang::__lifetimebound__]]; }; a &a::b() {} ``` This only crashes with `-target i686-w64-mingw32`. `bin/clang++ -c a.cpp` works fine. Problematic merging logic: ```cpp // If Old has lifetimebound but New doesn't, add it to New. if (OldLBAttr && !NewLBAttr) { QualType NewMethodType = New->getType(); QualType AttributedType = S.Context.getAttributedType(OldLBAttr, NewMethodType, NewMethodType); TypeLocBuilder TLB; TLB.pushFullCopy(NewTSI->getTypeLoc()); AttributedTypeLoc TyLoc = TLB.push<AttributedTypeLoc>(AttributedType); // Crashes. TyLoc.setAttr(OldLBAttr); New->setType(AttributedType); New->setTypeSourceInfo(TLB.getTypeSourceInfo(S.Context, AttributedType)); } ``` <details> <summary>Crash</summary> ``` clang++: /REDACTED//llvm-project/clang/lib/Sema/TypeLocBuilder.cpp:89: TypeLoc clang::TypeLocBuilder::pushImpl(QualType, size_t, unsigned int): Assertion `TLast == LastTy && "mismatch between last type and new type's inner type"' failed. PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace, preprocessed source, and associated run script. Stack dump: 0. Program arguments: bin/clang++ -target i686-w64-mingw32 -c /REDACTED//a.cpp 1. /REDACTED//a.cpp:4:11: current parser token '{' #0 0x000055971cfcb838 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) /REDACTED//llvm-project/llvm/lib/Support/Unix/Signals.inc:842:13 #1 0x000055971cfc9374 llvm::sys::RunSignalHandlers() /REDACTED//llvm-project/llvm/lib/Support/Signals.cpp:109:18 #2 0x000055971cfcaf0c llvm::sys::CleanupOnSignal(unsigned long) /REDACTED//llvm-project/llvm/lib/Support/Unix/Signals.inc:0:3 #3 0x000055971cf38116 (anonymous namespace)::CrashRecoveryContextImpl::HandleCrash(int, unsigned long) /REDACTED//llvm-project/llvm/lib/Support/CrashRecoveryContext.cpp:73:5 #4 0x000055971cf38116 CrashRecoverySignalHandler(int) /REDACTED//llvm-project/llvm/lib/Support/CrashRecoveryContext.cpp:390:51 #5 0x00007fe9ebe49df0 (/lib/x86_64-linux-gnu/libc.so.6+0x3fdf0) #6 0x00007fe9ebe9e95c __pthread_kill_implementation ./nptl/pthread_kill.c:44:76 #7 0x00007fe9ebe49cc2 raise ./signal/../sysdeps/posix/raise.c:27:6 #8 0x00007fe9ebe324ac abort ./stdlib/abort.c:81:3 llvm#9 0x00007fe9ebe32420 __assert_perror_fail ./assert/assert-perr.c:31:1 llvm#10 0x000055971f969ade clang::TypeLocBuilder::pushImpl(clang::QualType, unsigned long, unsigned int) /REDACTED//llvm-project/clang/lib/Sema/TypeLocBuilder.cpp:93:3 llvm#11 0x000055971f237255 clang::QualType::hasLocalQualifiers() const /REDACTED//llvm-project/clang/include/clang/AST/TypeBase.h:1065:37 llvm#12 0x000055971f237255 clang::ConcreteTypeLoc<clang::UnqualTypeLoc, clang::AttributedTypeLoc, clang::AttributedType, clang::AttributedLocInfo>::isKind(clang::TypeLoc const&) /REDACTED//llvm-project/clang/include/clang/AST/TypeLoc.h:392:26 llvm#13 0x000055971f237255 clang::AttributedTypeLoc clang::TypeLoc::castAs<clang::AttributedTypeLoc>() const /REDACTED//llvm-project/clang/include/clang/AST/TypeLoc.h:79:5 llvm#14 0x000055971f237255 clang::AttributedTypeLoc clang::TypeLocBuilder::push<clang::AttributedTypeLoc>(clang::QualType) /REDACTED//llvm-project/clang/lib/Sema/TypeLocBuilder.h:106:47 llvm#15 0x000055971f280cc8 clang::AttributedTypeLoc::setAttr(clang::Attr const*) /REDACTED//llvm-project/clang/include/clang/AST/TypeLoc.h:1035:30 llvm#16 0x000055971f280cc8 mergeLifetimeBoundAttrOnMethod(clang::Sema&, clang::CXXMethodDecl*, clang::CXXMethodDecl const*) /REDACTED//llvm-project/clang/lib/Sema/SemaDecl.cpp:4497:11 llvm#17 0x000055971f280cc8 clang::Sema::MergeCompatibleFunctionDecls(clang::FunctionDecl*, clang::FunctionDecl*, clang::Scope*, bool) /REDACTED//llvm-project/clang/lib/Sema/SemaDecl.cpp:4528:5 llvm#18 0x000055971f27eb1f clang::Sema::MergeFunctionDecl(clang::FunctionDecl*, clang::NamedDecl*&, clang::Scope*, bool, bool) /REDACTED//llvm-project/clang/lib/Sema/SemaDecl.cpp:0:0 llvm#19 0x000055971f29c256 clang::Sema::CheckFunctionDeclaration(clang::Scope*, clang::FunctionDecl*, clang::LookupResult&, bool, bool) /REDACTED//llvm-project/clang/lib/Sema/SemaDecl.cpp:12371:9 llvm#20 0x000055971f28dab0 clang::Declarator::setRedeclaration(bool) /REDACTED//llvm-project/clang/include/clang/Sema/DeclSpec.h:2738:51 llvm#21 0x000055971f28dab0 clang::Sema::ActOnFunctionDeclarator(clang::Scope*, clang::Declarator&, clang::DeclContext*, clang::TypeSourceInfo*, clang::LookupResult&, llvm::MutableArrayRef<clang::TemplateParameterList*>, bool&) /REDACTED//llvm-project/clang/lib/Sema/SemaDecl.cpp:10877:9 llvm#22 0x000055971f2890fc clang::Sema::HandleDeclarator(clang::Scope*, clang::Declarator&, llvm::MutableArrayRef<clang::TemplateParameterList*>) /REDACTED//llvm-project/clang/lib/Sema/SemaDecl.cpp:0:11 llvm#23 0x000055971f2aab99 clang::Sema::ActOnStartOfFunctionDef(clang::Scope*, clang::Declarator&, llvm::MutableArrayRef<clang::TemplateParameterList*>, clang::SkipBodyInfo*, clang::Sema::FnBodyKind) /REDACTED//llvm-project/clang/lib/Sema/SemaDecl.cpp:15904:15 llvm#24 0x000055971efab286 clang::Parser::ParseFunctionDefinition(clang::ParsingDeclarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::LateParsedAttrList*) /REDACTED//llvm-project/clang/lib/Parse/Parser.cpp:1364:23 llvm#25 0x000055971f013b40 clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&, clang::DeclaratorContext, clang::ParsedAttributes&, clang::Parser::ParsedTemplateInfo&, clang::SourceLocation*, clang::Parser::ForRangeInit*) /REDACTED//llvm-project/clang/lib/Parse/ParseDecl.cpp:2268:18 llvm#26 0x000055971efaa54f clang::Parser::ParseDeclOrFunctionDefInternal(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec&, clang::AccessSpecifier) /REDACTED//llvm-project/clang/lib/Parse/Parser.cpp:0:10 llvm#27 0x000055971efa9e36 clang::Parser::ParseDeclarationOrFunctionDefinition(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*, clang::AccessSpecifier) /REDACTED//llvm-project/clang/lib/Parse/Parser.cpp:1202:12 llvm#28 0x000055971efa8df8 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) /REDACTED//llvm-project/clang/lib/Parse/Parser.cpp:0:14 llvm#29 0x000055971efa7574 clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) /REDACTED//llvm-project/clang/lib/Parse/Parser.cpp:743:10 llvm#30 0x000055971ef9c0ee clang::ParseAST(clang::Sema&, bool, bool) /REDACTED//llvm-project/clang/lib/Parse/ParseAST.cpp:169:5 llvm#31 0x000055971dbcdad6 clang::FrontendAction::Execute() /REDACTED//llvm-project/clang/lib/Frontend/FrontendAction.cpp:1317:10 llvm#32 0x000055971db3c5fd llvm::Error::getPtr() const /REDACTED//llvm-project/llvm/include/llvm/Support/Error.h:278:42 llvm#33 0x000055971db3c5fd llvm::Error::operator bool() /REDACTED//llvm-project/llvm/include/llvm/Support/Error.h:241:16 llvm#34 0x000055971db3c5fd clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) /REDACTED//llvm-project/clang/lib/Frontend/CompilerInstance.cpp:1006:23 llvm#35 0x000055971dcb4f9c clang::ExecuteCompilerInvocation(clang::CompilerInstance*) /REDACTED//llvm-project/clang/lib/FrontendTool/ExecuteCompilerInvocation.cpp:310:25 llvm#36 0x000055971a5e655e cc1_main(llvm::ArrayRef<char const*>, char const*, void*) /REDACTED//llvm-project/clang/tools/driver/cc1_main.cpp:304:15 llvm#37 0x000055971a5e29cb ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&, llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem>) /REDACTED//llvm-project/clang/tools/driver/driver.cpp:226:12 llvm#38 0x000055971a5e4c1d clang_main(int, char**, llvm::ToolContext const&)::$_0::operator()(llvm::SmallVectorImpl<char const*>&) const /REDACTED//llvm-project/clang/tools/driver/driver.cpp:0:12 llvm#39 0x000055971a5e4c1d int llvm::function_ref<int (llvm::SmallVectorImpl<char const*>&)>::callback_fn<clang_main(int, char**, llvm::ToolContext const&)::$_0>(long, llvm::SmallVectorImpl<char const*>&) /REDACTED//llvm-project/llvm/include/llvm/ADT/STLFunctionalExtras.h:46:12 llvm#40 0x000055971d9bfe79 clang::driver::CC1Command::Execute(llvm::ArrayRef<std::optional<llvm::StringRef>>, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>*, bool*) const::$_0::operator()() const /REDACTED//llvm-project/clang/lib/Driver/Job.cpp:442:30 llvm#41 0x000055971d9bfe79 void llvm::function_ref<void ()>::callback_fn<clang::driver::CC1Command::Execute(llvm::ArrayRef<std::optional<llvm::StringRef>>, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>*, bool*) const::$_0>(long) /REDACTED//llvm-project/llvm/include/llvm/ADT/STLFunctionalExtras.h:46:12 llvm#42 0x000055971cf37dbe llvm::function_ref<void ()>::operator()() const /REDACTED//llvm-project/llvm/include/llvm/ADT/STLFunctionalExtras.h:0:12 llvm#43 0x000055971cf37dbe llvm::CrashRecoveryContext::RunSafely(llvm::function_ref<void ()>) /REDACTED//llvm-project/llvm/lib/Support/CrashRecoveryContext.cpp:426:3 llvm#44 0x000055971d9bf5ac clang::driver::CC1Command::Execute(llvm::ArrayRef<std::optional<llvm::StringRef>>, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>>*, bool*) const /REDACTED//llvm-project/clang/lib/Driver/Job.cpp:442:7 llvm#45 0x000055971d98422c clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const /REDACTED//llvm-project/clang/lib/Driver/Compilation.cpp:196:15 llvm#46 0x000055971d984447 clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&, bool) const /REDACTED//llvm-project/clang/lib/Driver/Compilation.cpp:246:13 llvm#47 0x000055971d99ee08 llvm::SmallVectorBase<unsigned int>::empty() const /REDACTED//llvm-project/llvm/include/llvm/ADT/SmallVector.h:83:46 llvm#48 0x000055971d99ee08 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl<std::pair<int, clang::driver::Command const*>>&) /REDACTED//llvm-project/clang/lib/Driver/Driver.cpp:2265:23 llvm#49 0x000055971a5e2303 clang_main(int, char**, llvm::ToolContext const&) /REDACTED//llvm-project/clang/tools/driver/driver.cpp:414:21 llvm#50 0x000055971a5f2527 main /usr/local/google/home/usx/build/tools/clang/tools/driver/clang-driver.cpp:17:10 llvm#51 0x00007fe9ebe33ca8 __libc_start_call_main ./csu/../sysdeps/nptl/libc_start_call_main.h:74:3 llvm#52 0x00007fe9ebe33d65 call_init ./csu/../csu/libc-start.c:128:20 llvm#53 0x00007fe9ebe33d65 __libc_start_main ./csu/../csu/libc-start.c:347:5 llvm#54 0x000055971a5e0361 _start (bin/clang+++0x6636361) clang++: error: clang frontend command failed with exit code 134 (use -v to see invocation) clang version 23.0.0git (https://github.com/llvm/llvm-project.git 282a065) Target: i686-w64-windows-gnu Thread model: posix InstalledDir: /usr/local/google/home/usx/build/bin Build config: +assertions clang++: note: diagnostic msg: ******************** ``` </details>
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finalizeGCNRegionan overridable hook (NFC)