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Loading 2 2x32-bit float vectors into the bottom half of a 256-bit vector produced suboptimal code in AVX2 mode with certain IR combinations. In particular, the IR optimizer folded 2f32 + 2f32 -> 4f32, 4f32 + 4f32 (undef) -> 8f32 into a 2f32 + 2f32 -> 8f32, which seems more canonical, but then mysteriously generated rather bad code; the movq/movhpd combination didn't match. The problem lay in the BUILD_VECTOR optimization path. The 2f32 inputs would get promoted to 4f32 by the type legalizer, eventually resulting in a BUILD_VECTOR on two 4f32 into an 8f32. The BUILD_VECTOR then, recognizing these were both half the output size, concatted them and then produced a shuffle. However, the resulting concat + shuffle was more complex than it should be; in the case where the upper half of the output is undef, we probably want to generate shuffle + concat instead. This enhancement causes the vector_shuffle combine step to recognize this suboptimal pattern and correct it. I included it there instead of in BUILD_VECTOR in case the same suboptimal pattern occurs for other reasons. This results in the optimizer correctly producing the optimal movq + movhpd sequence for all three variations on this IR, even with AVX2. I've included a test case. Radar link: rdar://problem/19287012 Fix for PR 21943. From: Fiona Glaser <fglaser@apple.com> git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@226360 91177308-0d34-0410-b5e6-96231b3b80d8 |
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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.