Craig Topper 77dbc5200b [MachineCSE] Use TargetInstrInfo::isAsCheapAsAMove in isPRECandidate. ...

Some targets like RISC-V require operands to be inspected to
determine if an instruction is similar to a move.

Spotted while investigating code differences between using an ADDI
vs an ADDIW. RISC-V has the isAsCheapAsAMove flag for ADDI, but
the TII hook checks the immediate is 0 or the register is X0. ADDIW
is never generated with X0 or with an immediate of 0 so it doesn't
have the isAsCheapAsAMove flag.

I don't know enough about the PRE code to write a test for this yet.

Reviewed By: reames

Differential Revision: https://reviews.llvm.org/D132981

2022-08-31 15:39:41 -07:00

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