Re: Can register rename pass rename a callee-saved register?

[Ian Lance Taylor <iant at google dot com>]

"Mohamed Shafi" <shafitvm@gmail.com> writes:

> Before register renaming pass, callee registers was being used in the
> body of the code. Hence function prologue saved the register and
> epilogue restored the register. But register renaming pass removed
> this particular callee saved register.The output and code generation
> is proper, but there is an unnecessary save and restore of a callee
> saved register in the prologue and epilogue even though the reference
> of the callee saved register has been removed by the renaming pass.
> I am using the prologue/epilogue patterns instead of the target macros.

Which version of gcc?  I was under the impression that this
longstanding buglet was cleaned up by the dataflow work.

> So is the rename pass allowed to rename a callee saved register? Where
> might this going wrong?

If this is the buglet I'm thinking of, the resulting code does work,
despite being suboptimal.  It just does an unnecessary save and
restore.

Ian