[RISCV][GISel] Emit G_CONSTANT 0 as a copy from X0. #67202
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topperc
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aemerson,
arsenm,
mshockwave,
michaelmaitland and
nitinjohnraj
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…LHS of sub for negate. I had to disable the late copy propagation pass that can see through the ADDI we were previously emitting. We really want to get this in the register coalescer if not even earlier.
We need to use a COPY so the register coalescer can replace reads of the register we copy to with X0. This is needed so that we use X0 on instructions that don't have an immediate form.
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michaelmaitland
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topperc
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We need to use a COPY so the register coalescer can replace reads of the register we copy to with X0. This is needed so that we use X0 on instructions that don't have an immediate form. This was reviewed as #67202.
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We need to use a COPY so the register coalescer can replace reads of the register we copy to with X0. This is needed so that we use X0 on instructions that don't have an immediate form.
I've added a roundtrip test for negate to show this. I had to disable the late copy propagation pass that could see through the ADDI.