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4f4bd24ec4
The motivation for this patch starts with the epic fail example in PR18007: https://llvm.org/bugs/show_bug.cgi?id=18007 ...unfortunately, this patch makes no difference for that case, but it solves some simpler cases. We'll get there some day. :) The current 'or' matching code was using computeKnownBits() via isBaseWithConstantOffset() -> MaskedValueIsZero(), but that's an unnecessarily limited use. We can do more by copying the logic in ValueTracking's haveNoCommonBitsSet(), so we can treat the 'or' as if it was an 'add'. There's a TODO comment here because we should lift the bit-checking logic into a helper function, so it's not duplicated in DAGCombiner. An example of the better LEA matching: leal (%rdi,%rdi), %eax andl $1, %esi orl %esi, %eax Becomes: andl $1, %esi leal (%rsi,%rdi,2), %eax Differential Revision: http://reviews.llvm.org/D13956 llvm-svn: 252515 |
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