[SystemZ] Use LCGR/AGHI for i64 XOR with -1 #74882
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Without the peephole, it produces instead LGHI/XGR, which uses one more register, although it is a constant load off the CP... |
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If we want to do that, the patch looks good. However, I'm still not 100% sure we do want to do it. The sequence is more compact, but we should also verify it has the same execution speed. (On some CPUs, the XILF and XIHF might be able to execute in parallel as they touch different halves of the GPR. The LCGR / AGHI always must be serialized.) We should check the performance on a small loop on actual machines. |
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LCGR/AGHI is a more compact way of implementing a 64-bit NOT.