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LLVM backend for 6502
c846d65f99
getSCEV for an ashr instruction creates an intermediate zext expression when it truncates its operand. The operand is initially inside the loop, so the narrow zext expression has a non-loop-invariant loop disposition. LoopSimplify then runs on an outer loop, hoists the ashr operand, and properly invalidate the SCEVs that are mapped to value. The SCEV expression for the ashr is now an AddRec with the hoisted value as the now loop-invariant start value. The LoopDisposition of this wide value was properly invalidated during LoopSimplify. However, if we later get the ashr SCEV again, we again try to create the intermediate zext expression. We get the same SCEV that we did earlier, and it is still cached because it was never mapped to a Value. When we try to create a new AddRec we abort because we're using the old non-loop-invariant LoopDisposition. I don't have a solution for this other than to clear LoopDisposition when LoopSimplify hoists things. I think the long-term strategy should be to perform LoopSimplify on all loops before computing SCEV and before running any loop opts on individual loops. It's possible we may want to rerun LoopSimplify on individual loops, but it should rarely do anything, so rarely require invalidating SCEV. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198478 91177308-0d34-0410-b5e6-96231b3b80d8 |
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