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authorNikita Popov <npopov@redhat.com>2024-08-14 09:37:38 +0200
committerGitHub <noreply@github.com>2024-08-14 09:37:38 +0200
commit6da3361f504495cef71caa4de4297234b6ea7fc7 (patch)
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[SCEV] Look through multiply in computeConstantDifference() (#103051)
Inside computeConstantDifference(), handle the case where both sides are of the form `C * %x`, in which case we can strip off the common multiplication (as long as we remember to multiply by it for the following difference calculation). There is an obvious alternative implementation here, which would be to directly decompose multiplies inside the "Multiplicity" accumulation. This does work, but I've found this to be both significantly slower (because everything has to work on APInt) and more complex in implementation (e.g. because we now need to match back the new More/Less with an arbitrary factor) without providing more power in practice. As such, I went for the simpler variant here. This is the last step to make computeConstantDifference() sufficiently powerful to replace existing uses of `cast<SCEVConstant>(getMinusSCEV())` with it.
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