forked from OSchip/llvm-project
c74322a11b
When a Tablegen instruction description uses `OperandWithDefaultOps`, isel patterns for that instruction don't have to fill in the default value for the operand in question. But the flip side is that they actually //can't// override the defaults even if they want to. This will be very inconvenient for the Arm backend, when we start wanting to write isel patterns that generate the many MVE predicated vector instructions, in the form with predication actually enabled. So this small Tablegen fix makes it possible to write an isel pattern either with or without values for a defaulted operand, and have the default values filled in only if they are not overridden. If all the defaulted operands come at the end of the instruction's operand list, there's a natural way to match them up to the arguments supplied in the pattern: consume pattern arguments until you run out, then fill in any missing instruction operands with their default values. But if defaulted and non-defaulted operands are interleaved, it's less clear what to do. This does happen in existing targets (the first example I came across was KILLGT, in the AMDGPU/R600 backend), and of course they expect the previous behaviour (that the default for those operands is used and a pattern argument is not consumed), so for backwards compatibility I've stuck with that. Reviewers: nhaehnle, hfinkel, dmgreen Subscribers: mehdi_amini, javed.absar, tpr, kristof.beyls, steven_wu, dexonsmith, llvm-commits Tags: #llvm Differential Revision: https://reviews.llvm.org/D63814 llvm-svn: 365114 |
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README.txt
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