forked from OSchip/llvm-project
3d15b7e7df
Function `replaceMathCmpWithIntrinsic` artificially limits the scope of the optimization, setting a requirement of two instructions be in the same block, due to two reasons: - usage of DT for more general check is costly in terms of compile time; - risk of creating a new value that lives through multiple blocks. Because of this, two semantically equivalent tests may be or not be the subject of this opt depending on where the binary operation is located. See `test/CodeGen/X86/usub_inc_iv.ll` for motivation There is one important particular case where this limitation is too strict: it is when the binary operation is the increment of the induction variable. As result, the application of this opt becomes fragile and highly reliant on where other passes decide to place IV increment. In most cases, they place it in the end of the latch block, killing the opt opportunity (when in fact it does not matter where to insert the actual instruction). This patch handles this particular case separately. - The detector does not use dom tree and has constant cost; - The value of IV or IV.next lives through all loop in any case, so this should not create a new unexpected long-living value. As result, the transform becomes more robust. It also seems to lead to better code generation in some cases (see `test/CodeGen/X86/lsr-loop-exit-cond.ll`). Differential Revision: https://reviews.llvm.org/D96119 Reviewed By: spatel, reames |
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README.txt
The LLVM Compiler Infrastructure ================================ 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.