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Re: Combine performance regression (was: Fix PR target/18701)
- From: Hans-Peter Nilsson <hp at bitrange dot com>
- To: Roger Sayle <roger at eyesopen dot com>
- Cc: Ulrich Weigand <uweigand at de dot ibm dot com>, gcc-patches at gcc dot gnu dot org
- Date: Tue, 25 Jan 2005 18:49:50 -0500 (EST)
- Subject: Re: Combine performance regression (was: Fix PR target/18701)
- References: <Pine.LNX.4.44.0501200919540.19161-100000@www.eyesopen.com>
On Thu, 20 Jan 2005, Roger Sayle wrote:
> I think this entire clause in combine_simplify_rtx isn't required
> and can be deleted. I'm currently bootstrapping and regression
> testing that change.
I assume you're talking about combine.c:1.471:3986:
/* Don't change the mode of the MEM if that would change the meaning
of the address. */
if (MEM_P (SUBREG_REG (x))
&& (MEM_VOLATILE_P (SUBREG_REG (x))
|| mode_dependent_address_p (XEXP (SUBREG_REG (x), 0))))
return gen_rtx_CLOBBER (mode, const0_rtx);
(Which is either correct or likely what together with the other
bug confused me into thinking that something else could
somewhat-validly change the mode of the memory access. Why else
would this code care whether the address is a
mode_dependent_address_p? FWIW, no, I still haven't revisited
this thoroughly yet.)
How did that test go?
brgds, H-P