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By definition copies across register banks are not coalescable. Still, it may be possible to get rid of such a copy when the value is available in another register of the same register file. Consider the following example, where capital and lower letters denote different register file: b = copy A <-- cross-bank copy ... C = copy b <-- cross-bank copy This could have been optimized this way: b = copy A <-- cross-bank copy ... C = copy A <-- same-bank copy Note: b and C's definitions may be in different basic blocks. This patch adds a peephole optimization that looks through a chain of copies leading to a cross-bank copy and reuses a source that is on the same register file if available. This solution could also be used to get rid of some copies (e.g., A could have been used instead of C). However, we do not do so because: - It may over constrain the coloring of the source register for coalescing. - The register allocator may not be able to find a nice split point for the longer live-range, leading to more spill. <rdar://problem/14742333> git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@190713 91177308-0d34-0410-b5e6-96231b3b80d8 |
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| LICENSE.TXT | ||
| llvm.spec.in | ||
| LLVMBuild.txt | ||
| Makefile | ||
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| README.txt | ||
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.