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Do not apply the flags of a conditional instruction in TransformConstDst - #516
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totalspectrum merged 1 commit intoOct 11, 2026
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A conditional instruction sets its flags only where its condition holds, so after it they are not known. TransformConstDst handed them to ApplyConditionAfter anyway: `if_e cmp f, #0 wz` folded as an unconditional compare turned the `if_e jmp` after it into a jmp, and `(12 != g) || f` came out 0 for a g of 0 (flexprop issue 118). Test/cexec06.c is the reproducer as a hardware test.
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Thanks for your contribution! This was very nice, and having it as a pull request for spin2cpp made it easy to merge. I'll address your other questions on the flexprop bug. |
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This is the fix suggested in item 1 of totalspectrum/flexprop#118, with a test.
TransformConstDst folds an instruction whose operands are known, and hands the
flags it would set to ApplyConditionAfter without looking at
ir->cond. Aconditional instruction sets its flags only where its condition holds, so after it
they are not known. In the #118 reproducer,
if_e cmp f, #0 wzwas folded as anunconditional compare, the
if_e jmpafter it became ajmp, and(12 != g) || fcame out 0 for agof 0.The change returns early for a conditional instruction, as OptimizeCompares and the
constant moves in OptimizeMoves already do.
Test/cexec06.cis the reproducer as a hardware test. It prints0 1without thechange and
1 1with it.Checked, with flexspin built from this branch (master eb26396 plus this commit):
make test_offline: the same tests pass as on master.Test/runtests_p2.shon a P2-EDGE: 27 of 27 pass, cexec06 included.compile differently. All six run correctly on the board with the change, and one
of them fails without it.
Item 2 of #118 (the hang at nine nested calls) and item 3 (the question) are not
touched here.