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Re: PR rtl-optimization/15248 -- semi-latent reload bug

Jeffrey A Law wrote:
On Thu, 2005-05-05 at 19:22 +0200, Bernd Schmidt wrote:

Jeffrey A Law wrote:

On Thu, 2005-04-21 at 20:52 +0200, Bernd Schmidt wrote:

Yes, that is exactly the thing that I'm not getting here. If the pseudo is equivalent to readonly memory, why is it ever written to?

Because in the initial insn stream the pseudo had to be initialized. It's the replacement of the pseudo with its equivalent memory location in the initializing insn that causes the fault.

Normally the initialization insns are removed.  However, that's not the
case if the RHS of the equivalencing insn is not the equivalent
memory location (in this case the RHS of the equivalencing insn is
another pseudo which we know happens to hold the proper value).

Ok. Still, we should be able to delete the initializing insn in this case if it has no other side effects, correct?

Assuming you can find them all and safely eliminate the store side affect. Again, consider that the store might be buried inside a PARALLEL. That's a non-trivial problem.

Could be done by forcing an output reload that doesn't get stored anywhere. We have machinery to do this for regs with REG_UNUSED notes etc.


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