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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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