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Re: [PATCH, rtl-optimization]: Fix PR rtl-optimization/33638

> Eric, i am not arguing that my code in dse should stay the way that it
> is, i was just hoping somehow i could salvage the ability to do better
> things for accesses off of the frame pointer.

No disagreement. :-)  I'm still trying to figure out whether flow.c would 
handle this correctly with the help of CALL_INSN_FUNCTION_USAGE.

Note that dse.c also uses the alias.c machinery (canon_rtx), which is global.
I'm under the impression that by enhancing a little this machinery, we could 
match the ability of gcse.c to detect that the stack pointer is invariant in 
the function; if we had this, canon_rtx would return the right thing.

> Another issue that this brings up is the code that deletes stores into
> the frame pointer that die when the function returns.  I am now a little
> worried that code may be also compromised.  If i am able to see the
> store as being relative to the frame but there is some load whose
> address has been stored in a register, i am screwed.

This should be more or less an equivalent problem.

Eric Botcazou

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