forked from OSchip/llvm-project
ec06b38130
This reverses the existing transform that would uniformly canonicalize any 'xor' after any shift. In the case of logical shifts, that turns a 'not' into an arbitrary 'xor' with constant, and that's probably not as good for analysis, SCEV, or codegen. The SCEV motivating case is discussed in: http://bugs.llvm.org/PR47136 There's an analysis motivating case at: http://bugs.llvm.org/PR38781 I did draft a patch that would do the same for 'ashr' but that's questionable because it's just swapping the position of a 'not' and uncovers at least 2 missing folds that we would probably need to deal with as preliminary steps. Alive proofs: https://rise4fun.com/Alive/BBV Name: shift right of 'not' Pre: C2 == (-1 u>> C1) %a = lshr i8 %x, C1 %r = xor i8 %a, C2 => %n = xor i8 %x, -1 %r = lshr i8 %n, C1 Name: shift left of 'not' Pre: C2 == (-1 << C1) %a = shl i8 %x, C1 %r = xor i8 %a, C2 => %n = xor i8 %x, -1 %r = shl i8 %n, C1 Name: ashr of 'not' %a = ashr i8 %x, C1 %r = xor i8 %a, -1 => %n = xor i8 %x, -1 %r = ashr i8 %n, C1 Differential Revision: https://reviews.llvm.org/D86243 |
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| .. | ||
| Analysis | ||
| Assembler | ||
| Bindings | ||
| Bitcode | ||
| BugPoint | ||
| CodeGen | ||
| DebugInfo | ||
| Demangle | ||
| Examples | ||
| ExecutionEngine | ||
| Feature | ||
| FileCheck | ||
| Instrumentation | ||
| Integer | ||
| JitListener | ||
| LTO | ||
| Linker | ||
| MC | ||
| MachineVerifier | ||
| Object | ||
| ObjectYAML | ||
| Other | ||
| Reduce | ||
| SafepointIRVerifier | ||
| Support | ||
| SymbolRewriter | ||
| TableGen | ||
| ThinLTO/X86 | ||
| Transforms | ||
| Unit | ||
| Verifier | ||
| YAMLParser | ||
| tools | ||
| .clang-format | ||
| CMakeLists.txt | ||
| TestRunner.sh | ||
| lit.cfg.py | ||
| lit.site.cfg.py.in | ||