mirror of
https://github.com/c64scene-ar/llvm-6502.git
synced 2025-02-01 17:32:36 +00:00
3bd732d1ee
For some history here see the commit messages of r199797 and r169060. The original intent was to fix cases like: %EAX<def> = COPY %ECX<kill>, %RAX<imp-def> %RCX<def> = COPY %RAX<kill> where simply removing the copies would have RCX undefined as in terms of machine operands only the ECX part of it is defined. The machine verifier would complain about this so 169060 changed such COPY instructions into KILL instructions so some super-register imp-defs would be preserved. In r199797 it was finally decided to always do this regardless of super-register defs. But this is wrong, consider: R1 = COPY R0 ... R0 = COPY R1 getting changed to: R1 = KILL R0 ... R0 = KILL R1 It now looks like R0 dies at the first KILL and won't be alive until the second KILL, while in reality R0 is alive and must not change in this part of the program. As this only happens after register allocation there is not much code still performing liveness queries so the issue was not noticed. In fact I didn't manage to create a testcase for this, without unrelated changes I am working on at the moment. The fix is simple: As of r223896 the MachineVerifier allows reads from partially defined registers, so the whole transforming COPY->KILL thing is not necessary anymore. This patch also changes a similar (but more benign case as the def and src are the same register) case in the VirtRegRewriter. Differential Revision: http://reviews.llvm.org/D10117 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@238588 91177308-0d34-0410-b5e6-96231b3b80d8
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're writing a package for LLVM, see docs/Packaging.rst for our suggestions.