[glampert]

Follow-up to #11.

Problem

A code block's out_vf/out_vi outputs could leave in the wrong register, or be overwritten before the exit, in two ways:

1. Paths through a taken branch ignored the outputs. The register allocator walks the program path by path; the path that takes a conditional branch is a copy of the state before it, and BranchState's copy constructor copied the inputs but not the outputs. A value assigned before the branch and left alone on the taken path never got its output register:

       move fOut, fA
       ibeq iFlag, vi00, lDone
       add  fOut, fA, fA
   lDone:
       --exit
       out_vf fOut(vf05)

compiled the move as move VF02, VF01, so the taken path left with VF05 never written.

2. An output's live range ended at its last access, not at the exit. A temporary needed after that point could take the output's register before the program ended (add fOut, fA, fA then add fT, fA, fA / sq fT, 0(vi00) gave fT VF05, the register out_vf fOut(vf05) names). An input passed straight through to an output had no range at all.

Fix

• Copy the outputs into the branch states.
• In completeLiveRanges, the exit reads every output: each read joins the writes that reach it, is live from them to the end of the block, and takes the register its directive names. When the value it sees is an input in another register, that is reported: error: Register conflict: fA has to be in both VF01 and VF05.

Tests

test/integration/test_exit_outputs.cpp, 4 new cases:

• an output assigned before a taken branch gets its register;
• an output keeps its register until the exit (VF and VI);
• an input passed through to an output keeps its register;
• an output that wants an input's value in another register is an error.

Effect on generated code

None of the ps2gl fixtures, Tyra's 15 programs or quake2-ps2's programs use outputs: all compile byte-identically to master (a5e9dbe). The test suite and an ASan/UBSan build of the suite and those programs are clean.