[PATCH] D75098: Add TCOPY, a terminator form of the COPY instr

[Bill Wendling via Phabricator via llvm-commits]

void added inline comments.


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Comment at: llvm/include/llvm/CodeGen/MachineInstr.h:1121
+    return getOpcode() == TargetOpcode::COPY ||
+        getOpcode() == TargetOpcode::COPY_BR;
   }
----------------
arsenm wrote:
> void wrote:
> > nickdesaulniers wrote:
> > > Does this save a few `getOpcode()` calls? The rest of this CL explicitly compares the opcode against `COPY_BR`? I just worry if this might mess up existing callsites of `isCopy` when `getOpcode() == TargetOpcode::COPY_BR;`.
> > It's more than just a few. `isCopy()` is used pretty extensively. I want the `COPY_BR` (or `COPY_TERM`) to be exactly like a normal `COPY`, with the only exception that it can come after a terminator.
> I think this is potentially hazardous. I'm worried about the peephole optimizer doing things like folding a copy into a tcopy and losing the terminator bit. Can you add some testcases with coalescable tcopy pairs for PeepholeOptimizer and the register coalescer?
I'll craft some tests, though note that TCOPY should only be after a terminator, so a COPY should never be merged with it. (I'll add a verifier check to ensure that TCOPY doesn't happen before a terminator.)


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  https://reviews.llvm.org/D75098/new/

https://reviews.llvm.org/D75098