forked from OSchip/llvm-project
d67165c93c
Summary: Many languages have a three way comparison idiom where comparing two values produces not a boolean, but a tri-state value. Typical values (e.g. as used in the lcmp/fcmp bytecodes from Java) are -1 for less than, 0 for equality, and +1 for greater than. We actually do a great job already of converting three way comparisons into binary comparisons when the result produced has one a single use. Unfortunately, such values can have more than one use, and in that case, our existing optimizations break down. The patch adds a peephole which converts a three-way compare + test idiom into a binary comparison on the original inputs. It focused on replacing the test on the result of the three way compare and does nothing about removing the three way compare itself. That's left to other optimizations (which do actually kick in commonly.) We currently recognize one idiom on signed integer compare. In the future, we plan to recognize and simplify other comparison idioms on other signed/unsigned datatypes such as floats, vectors etc. This is a resurrection of Philip Reames' original patch: https://reviews.llvm.org/D19452 Reviewers: majnemer, apilipenko, reames, sanjoy, mkazantsev Reviewed by: mkazantsev Subscribers: llvm-commits Differential Revision: https://reviews.llvm.org/D34278 llvm-svn: 306100 |
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| .. | ||
| CMakeLists.txt | ||
| InstCombineAddSub.cpp | ||
| InstCombineAndOrXor.cpp | ||
| InstCombineCalls.cpp | ||
| InstCombineCasts.cpp | ||
| InstCombineCompares.cpp | ||
| InstCombineInternal.h | ||
| InstCombineLoadStoreAlloca.cpp | ||
| InstCombineMulDivRem.cpp | ||
| InstCombinePHI.cpp | ||
| InstCombineSelect.cpp | ||
| InstCombineShifts.cpp | ||
| InstCombineSimplifyDemanded.cpp | ||
| InstCombineVectorOps.cpp | ||
| InstructionCombining.cpp | ||
| LLVMBuild.txt | ||