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Re: [PATCH v2] Simplify pow with constant
On Thu, 17 Aug 2017, Wilco Dijkstra wrote:
> This patch simplifies pow (C, x) into exp (x * C1) if C > 0, C1 = log (C).
Note this changes the outcome for C == +Inf, x == 0 (pow is specified to
return 1.0 in that case, but x * C1 == NaN). There's another existing
transform with the same issue, 'pow(expN(x), y) -> expN(x*y)', so this is
not a new problem.
The whole set of these match.pd transforms is guarded by
flag_unsafe_math_optimizations, which is a bit strange, on the one hand
it does not include -ffinite-math-only, but on the other hand it's
defined broadly enough to imply that.
(to be clear, I'm not objecting to the patch, just pointing out an
existing inconsistency in case someone can offer clarifications)
Alexander