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LLVM backend for 6502
movw. That is we promote the destination operand to r16. So %CH = TRUNC_R16_R8 %BP is emitted as movw %bp, %cx. This is incorrect. If %cl is live, it would be clobbered. Ideally we want to do the opposite, that is emitted it as movb ??, %ch But this is not possible since %bp does not have a r8 sub-register. We are now defining a new register class R16_ which is a subclass of R16 containing only those 16-bit registers that have r8 sub-registers (i.e. AX - DX). We isel the truncate to two instructions, a MOV16to16_ to copy the value to the R16_ class, followed by a TRUNC_R16_R8. Due to bug 770, the register colaescer is not going to coalesce between R16 and R16_. That will be fixed later so we can eliminate the MOV16to16_. Right now, it can only be eliminated if we are lucky that source and destination registers are the same. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@28164 91177308-0d34-0410-b5e6-96231b3b80d8 |
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