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Re: [patch] Fold x + x to x * 2


> Zdenek Dvorak wrote:
>
> during investigation of PR 17549 I noted that we do not fold x + x to x
> * 2.  We also do not fold x * c + x to x * (c + 1).  (For non-floats.
> For floats we do both, under some assumptions.)  In the case of PR
> 17549, the ivopts end up producing expressions of type x+x+...+x with as
> much as 8 operands (the expressions are then somehow folded in RTL
> optimizers, I think, so we do not end up producing these sums and it
> does not affect size of the final code, but still this behavior is quite
> weird).  This patch implements these transformations.

How is perceived that (2 * x) is preferable to (x + x), as in general
it's most likely not?

even (x + x + x + x) would guess should likely only be target neutrally
folded to (t = (x + x), (t + t)), not (4 * x); where then based on the
target machine, likely to (x << 2) or (x * 4), but not before.

Do I misunderstand?



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