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Mirror of https://github.com/RPCS3/llvm-mirror
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Unfortunately, the PowerPC instruction definitions make heavy use of the positional operand encoding heuristic to map operands onto bitfield variables in the instruction definitions. Changing this to use name-based mapping is not trivial, however, because additional infrastructure needs to be designed to handle mapping of complex operands (with multiple suboperands) onto multiple bitfield variables. In the mean time, this adds support for positionally encoded operands to FixedLenDecoderEmitter, so that we can generate a disassembler for the PowerPC backend. To prevent an accidental reliance on this feature, and to prevent an undesirable interaction with existing disassemblers, a backend must opt-in to this support by setting the new decodePositionallyEncodedOperands instruction-set bit to true. When enabled, this iterates the variables that contribute to the instruction encoding, just as the encoder does, and emulates the procedure the encoder uses to map "numbered" operands to variables. The bit range for each variable is also determined as the encoder determines them. This map is then consulted during the decoder-generator's loop over operands to decode, allowing the decoder to understand both position-based and name-based operand-to-variable mappings. As noted in the comment on the decodePositionallyEncodedOperands definition, this support should be removed once it is no longer needed. There should be no change to existing disassemblers. llvm-svn: 197691 |
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Low Level Virtual Machine (LLVM) ================================ This directory and its subdirectories contain source code for the Low Level Virtual Machine, a toolkit for the construction of highly optimized compilers, optimizers, and runtime environments. LLVM is open source software. You may freely distribute it under the terms of the license agreement found in LICENSE.txt. Please see the documentation provided in docs/ for further assistance with LLVM, and in particular docs/GettingStarted.rst for getting started with LLVM and docs/README.txt for an overview of LLVM's documentation setup. If you're writing a package for LLVM, see docs/Packaging.rst for our suggestions.