8a757bba10
r187116 moved compare-and-branch generation from the instruction-selection pass to the peephole optimizer (via optimizeCompare). It turns out that even this is a bit too early. Fused compare-and-branch instructions don't interact well with predication, where a CC result is needed. They also make it harder to reuse the CC side-effects of earlier instructions (not yet implemented, but the subject of a later patch). Another problem was that the AnalyzeBranch family of routines weren't handling compares and branches, so we weren't able to reverse the fused form in cases where we would reverse a separate branch. This could have been fixed by extending AnalyzeBranch, but given the other problems, I've instead moved the fusing to the long-branch pass, which is also responsible for the opposite transformation: splitting out-of-range compares and branches into separate compares and long branches. I've added a test for the AnalyzeBranch problem. A test for the predication problem is included in the next patch, which fixes a bug in the choice of CC mask. llvm-svn: 187494 |
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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.