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Kuniyuki Iwashima reported in [1] that llvm compiler may convert a loop exit condition with "i < bound" to "i != bound", where "i" is the loop index variable and "bound" is the upper bound. In case that "bound" is not a constant, verifier will always have "i != bound" true, which will cause verifier failure since to verifier this is an infinite loop. The fix is to avoid transforming "i < bound" to "i != bound". In llvm, the transformation is done by IndVarSimplify pass. The compiler checks loop condition cost (i = i + 1) and if the cost is lower, it may transform "i < bound" to "i != bound". This patch implemented getArithmeticInstrCost() in BPF TargetTransformInfo class to return a higher cost for such an operation, which will prevent the transformation for the test case added in this patch. [1] https://lore.kernel.org/netdev/1994df05-8f01-371f-3c3b-d33d7836878c@fb.com/ Differential Revision: https://reviews.llvm.org/D107483 (cherry picked from commit e52946b9ababcbf8e6f40b1b15900ae2e795a1c6) |
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