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8366289c89
The current demand propagator for addition will mark all input bits at and right of the alive output bit as alive. But carry won't propagate beyond a bit for which both operands are zero (or one/zero in the case of subtraction) so a more accurate answer is possible given known bits. I derived a propagator by working through truth tables and using a bit-reversed addition to make demand ripple to the right, but I'm not sure how to make a convincing argument for its correctness in the comments yet. Nevertheless, here's a minimal implementation and test to get feedback. This would help in a situation where, for example, four bytes (<128) packed into an int are added with four others SIMD-style but only one of the four results is actually read. Known A: 0_______0_______0_______0_______ Known B: 0_______0_______0_______0_______ AOut: 00000000001000000000000000000000 AB, current: 00000000001111111111111111111111 AB, patch: 00000000001111111000000000000000 Committed on behalf of: @rrika (Erika) Differential Revision: https://reviews.llvm.org/D72423 |
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| .. | ||
| DynamicLibrary | ||
| AlignmentTest.cpp | ||
| AlignOfTest.cpp | ||
| AllocatorTest.cpp | ||
| AnnotationsTest.cpp | ||
| ARMAttributeParser.cpp | ||
| ArrayRecyclerTest.cpp | ||
| Base64Test.cpp | ||
| BinaryStreamTest.cpp | ||
| BlockFrequencyTest.cpp | ||
| BranchProbabilityTest.cpp | ||
| CachePruningTest.cpp | ||
| Casting.cpp | ||
| CheckedArithmeticTest.cpp | ||
| Chrono.cpp | ||
| CMakeLists.txt | ||
| CommandLineTest.cpp | ||
| CompressionTest.cpp | ||
| ConvertUTFTest.cpp | ||
| CrashRecoveryTest.cpp | ||
| CRCTest.cpp | ||
| DataExtractorTest.cpp | ||
| DebugCounterTest.cpp | ||
| DebugTest.cpp | ||
| DJBTest.cpp | ||
| ELFAttributeParserTest.cpp | ||
| EndianStreamTest.cpp | ||
| EndianTest.cpp | ||
| ErrnoTest.cpp | ||
| ErrorOrTest.cpp | ||
| ErrorTest.cpp | ||
| ExtensibleRTTITest.cpp | ||
| FileCheckTest.cpp | ||
| FileCollectorTest.cpp | ||
| FileOutputBufferTest.cpp | ||
| FileUtilitiesTest.cpp | ||
| formatted_raw_ostream_test.cpp | ||
| FormatVariadicTest.cpp | ||
| GlobPatternTest.cpp | ||
| Host.cpp | ||
| IndexedAccessorTest.cpp | ||
| ItaniumManglingCanonicalizerTest.cpp | ||
| JSONTest.cpp | ||
| KnownBitsTest.cpp | ||
| KnownBitsTest.h | ||
| LEB128Test.cpp | ||
| LineIteratorTest.cpp | ||
| LockFileManagerTest.cpp | ||
| ManagedStatic.cpp | ||
| MatchersTest.cpp | ||
| MathExtrasTest.cpp | ||
| MD5Test.cpp | ||
| MemoryBufferTest.cpp | ||
| MemoryTest.cpp | ||
| NativeFormatTests.cpp | ||
| OptimizedStructLayoutTest.cpp | ||
| ParallelTest.cpp | ||
| Path.cpp | ||
| ProcessTest.cpp | ||
| ProgramTest.cpp | ||
| raw_ostream_test.cpp | ||
| raw_pwrite_stream_test.cpp | ||
| raw_sha1_ostream_test.cpp | ||
| RegexTest.cpp | ||
| ReplaceFileTest.cpp | ||
| ReverseIterationTest.cpp | ||
| RISCVAttributeParserTest.cpp | ||
| ScaledNumberTest.cpp | ||
| SourceMgrTest.cpp | ||
| SpecialCaseListTest.cpp | ||
| SuffixTreeTest.cpp | ||
| SwapByteOrderTest.cpp | ||
| SymbolRemappingReaderTest.cpp | ||
| TargetParserTest.cpp | ||
| TarWriterTest.cpp | ||
| TaskQueueTest.cpp | ||
| Threading.cpp | ||
| ThreadLocalTest.cpp | ||
| ThreadPool.cpp | ||
| TimerTest.cpp | ||
| ToolOutputFileTest.cpp | ||
| TrailingObjectsTest.cpp | ||
| TrigramIndexTest.cpp | ||
| TypeNameTest.cpp | ||
| TypeTraitsTest.cpp | ||
| UnicodeTest.cpp | ||
| VersionTupleTest.cpp | ||
| VirtualFileSystemTest.cpp | ||
| WithColorTest.cpp | ||
| xxhashTest.cpp | ||
| YAMLIOTest.cpp | ||
| YAMLParserTest.cpp | ||