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Re: [Patch] rtx_cost of SUBREG


> Relatively recently, Mark Dettinger has been doing the same for s390
> and s390x and I'm sure you've seen his backend bits on gcc-patches.

Yes, and I certainly don't mind them as they are not included in the typical 
SPARC 64-bit compiler. ;-)

> I concede that changing the default SUBREG cost, as with any middle-end
> change, was riskier.  However, yet again this is a bug-fix that
> should benefit most targets (and there was no reason to believe anything
> would break).  The cost on acessing these SUBREGs, even on sparc64,
> shouldn't been one instruction per operand.  Typically, the register
> allocator will place them in a suitable hard register.

Maybe not one, but are you sure of 0 for all targets?

> In further of my defense, bugs in this part of the compiler are now
> fixed almost as soon as they are reported, and correcting the latent
> bugs that are often exposed by these perturbations makes for a better
> compiler.  At worst, the change can always be reverted.

Well, it can be reverted after it has been pinpointed, which takes time, that 
could have been used to fix higher priority problems.

-- 
Eric Botcazou


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