AMDGPU: Fix DPP combiner using isOperandLegal on incomplete inst (#155595)
It is not safe to use isOperandLegal on an instruction that does
not have a complete set of operands. Unforunately the APIs are
not set up in a convenient way to speculatively check if an instruction
will be legal in a hypothetical instruction. Build all the operands
and then verify they are legal after. This is clumsy, we should have
a more direct check for will these operands give a legal instruction.
This seems to fix a missed optimization in the gfx11 test. The
fold was firing for gfx1150, but not gfx1100. Both should support
vop3 literals so I'm not sure why it wasn't working before.
llvm-project
bb54be58 - AMDGPU: Fix DPP combiner using isOperandLegal on incomplete inst (#155595)
