forked from OSchip/llvm-project
b32f3656d2
Currently, an instruction setting the condition code is linked to the instruction using the condition code via a "glue" link in the SelectionDAG. This has a number of drawbacks; in particular, it means the same CC cannot be used by multiple users. It also makes it more difficult to efficiently implement SADDO et. al. This patch changes the back-end to represent CC dependencies as normal values during SelectionDAG matching, along the lines of how this is handled in the X86 back-end already. In addition to the core mechanics of updating all relevant patterns, this requires a number of additional changes: - We now need to be able to spill/restore a CC value into a GPR if necessary. This means providing a copyPhysReg implementation for moves involving CC, and defining getCrossCopyRegClass. - Since we still prefer to avoid such spills, we provide an override for IsProfitableToFold to avoid creating a merged LOAD / ICMP if this would result in multiple users of the CC. - combineCCMask no longer requires a single CC user, and no longer need to be careful about preventing invalid glue/chain cycles. - emitSelect needs to be more careful in marking CC live-in to the basic block it generates. Also, we can now optimize the case of multiple subsequent selects with the same condition just like X86 does. llvm-svn: 331202 |
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README.txt
Low Level Virtual Machine (LLVM) ================================ This directory and its subdirectories contain source code for LLVM, 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 are writing a package for LLVM, see docs/Packaging.rst for our suggestions.