forked from OSchip/llvm-project
338be9c595
Currently Clang does not respect -fno-unroll-loops during LTO. During D76916 it was suggested to respect -fno-unroll-loops on a TU basis. This patch uses the existing llvm.loop.unroll.disable metadata to disable loop unrolling explicitly for each loop in the TU if unrolling is disabled. This should ensure that loops from TUs compiled with -fno-unroll-loops are skipped by the unroller during LTO. This also means that if a loop from a TU with -fno-unroll-loops gets inlined into a TU without this option, the loop won't be unrolled. Due to the fact that some transforms might drop loop metadata, there potentially are cases in which we still unroll loops from TUs with -fno-unroll-loops. I think we should fix those issues rather than introducing a function attribute to disable loop unrolling during LTO. Improving the metadata handling will benefit other use cases, like various loop pragmas, too. And it is an improvement to clang completely ignoring -fno-unroll-loops during LTO. If that direction looks good, we can use a similar approach to also respect -fno-vectorize during LTO, at least for LoopVectorize. In the future, this might also allow us to remove the UnrollLoops option LLVM's PassManagerBuilder. Reviewers: Meinersbur, hfinkel, dexonsmith, tejohnson Reviewed By: Meinersbur, tejohnson Differential Revision: https://reviews.llvm.org/D77058 |
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| .. | ||
| ABIInfo.h | ||
| Address.h | ||
| BackendUtil.cpp | ||
| CGAtomic.cpp | ||
| CGBlocks.cpp | ||
| CGBlocks.h | ||
| CGBuilder.h | ||
| CGBuiltin.cpp | ||
| CGCUDANV.cpp | ||
| CGCUDARuntime.cpp | ||
| CGCUDARuntime.h | ||
| CGCXX.cpp | ||
| CGCXXABI.cpp | ||
| CGCXXABI.h | ||
| CGCall.cpp | ||
| CGCall.h | ||
| CGClass.cpp | ||
| CGCleanup.cpp | ||
| CGCleanup.h | ||
| CGCoroutine.cpp | ||
| CGDebugInfo.cpp | ||
| CGDebugInfo.h | ||
| CGDecl.cpp | ||
| CGDeclCXX.cpp | ||
| CGException.cpp | ||
| CGExpr.cpp | ||
| CGExprAgg.cpp | ||
| CGExprCXX.cpp | ||
| CGExprComplex.cpp | ||
| CGExprConstant.cpp | ||
| CGExprScalar.cpp | ||
| CGGPUBuiltin.cpp | ||
| CGLoopInfo.cpp | ||
| CGLoopInfo.h | ||
| CGNonTrivialStruct.cpp | ||
| CGObjC.cpp | ||
| CGObjCGNU.cpp | ||
| CGObjCMac.cpp | ||
| CGObjCRuntime.cpp | ||
| CGObjCRuntime.h | ||
| CGOpenCLRuntime.cpp | ||
| CGOpenCLRuntime.h | ||
| CGOpenMPRuntime.cpp | ||
| CGOpenMPRuntime.h | ||
| CGOpenMPRuntimeNVPTX.cpp | ||
| CGOpenMPRuntimeNVPTX.h | ||
| CGRecordLayout.h | ||
| CGRecordLayoutBuilder.cpp | ||
| CGStmt.cpp | ||
| CGStmtOpenMP.cpp | ||
| CGVTT.cpp | ||
| CGVTables.cpp | ||
| CGVTables.h | ||
| CGValue.h | ||
| CMakeLists.txt | ||
| CodeGenABITypes.cpp | ||
| CodeGenAction.cpp | ||
| CodeGenFunction.cpp | ||
| CodeGenFunction.h | ||
| CodeGenModule.cpp | ||
| CodeGenModule.h | ||
| CodeGenPGO.cpp | ||
| CodeGenPGO.h | ||
| CodeGenTBAA.cpp | ||
| CodeGenTBAA.h | ||
| CodeGenTypeCache.h | ||
| CodeGenTypes.cpp | ||
| CodeGenTypes.h | ||
| ConstantEmitter.h | ||
| ConstantInitBuilder.cpp | ||
| CoverageMappingGen.cpp | ||
| CoverageMappingGen.h | ||
| EHScopeStack.h | ||
| ItaniumCXXABI.cpp | ||
| MacroPPCallbacks.cpp | ||
| MacroPPCallbacks.h | ||
| MicrosoftCXXABI.cpp | ||
| ModuleBuilder.cpp | ||
| ObjectFilePCHContainerOperations.cpp | ||
| PatternInit.cpp | ||
| PatternInit.h | ||
| README.txt | ||
| SanitizerMetadata.cpp | ||
| SanitizerMetadata.h | ||
| SwiftCallingConv.cpp | ||
| TargetInfo.cpp | ||
| TargetInfo.h | ||
| VarBypassDetector.cpp | ||
| VarBypassDetector.h | ||
README.txt
IRgen optimization opportunities. //===---------------------------------------------------------------------===// The common pattern of -- short x; // or char, etc (x == 10) -- generates an zext/sext of x which can easily be avoided. //===---------------------------------------------------------------------===// Bitfields accesses can be shifted to simplify masking and sign extension. For example, if the bitfield width is 8 and it is appropriately aligned then is is a lot shorter to just load the char directly. //===---------------------------------------------------------------------===// It may be worth avoiding creation of alloca's for formal arguments for the common situation where the argument is never written to or has its address taken. The idea would be to begin generating code by using the argument directly and if its address is taken or it is stored to then generate the alloca and patch up the existing code. In theory, the same optimization could be a win for block local variables as long as the declaration dominates all statements in the block. NOTE: The main case we care about this for is for -O0 -g compile time performance, and in that scenario we will need to emit the alloca anyway currently to emit proper debug info. So this is blocked by being able to emit debug information which refers to an LLVM temporary, not an alloca. //===---------------------------------------------------------------------===// We should try and avoid generating basic blocks which only contain jumps. At -O0, this penalizes us all the way from IRgen (malloc & instruction overhead), all the way down through code generation and assembly time. On 176.gcc:expr.ll, it looks like over 12% of basic blocks are just direct branches! //===---------------------------------------------------------------------===//