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LLVM backend for 6502
299fdd814f
The main complication here is that TM and TMY (the memory forms) set CC differently from the register forms. When the tested bits contain some 0s and some 1s, the register forms set CC to 1 or 2 based on the value the uppermost bit. The memory forms instead set CC to 1 regardless of the uppermost bit. Until now, I've tried to make it so that a branch never tests for an impossible CC value. E.g. NR only sets CC to 0 or 1, so branches on the result will only test for 0 or 1. Originally I'd tried to do the same thing for TM and TMY by using custom matching code in ISelDAGToDAG. That ended up being very ugly though, and would have meant duplicating some of the chain checks that the common isel code does. I've therefore gone for the simpler alternative of adding an extra operand to the TM DAG opcode to say whether a memory form would be OK. This means that the inverse of a "TM;JE" is "TM;JNE" rather than the more precise "TM;JNLE", just like the inverse of "TMLL;JE" is "TMLL;JNE". I suppose that's arguably less confusing though... git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@190400 91177308-0d34-0410-b5e6-96231b3b80d8 |
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