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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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