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Date: Thu, 16 Apr 2020 20:21:40 -0500
From: Segher Boessenkool <segher@kernel.crashing.org>
To: luoxhu--- via Gcc-patches <gcc-patches@gcc.gnu.org>, luoxhu@linux.ibm.com, 
 wschmidt@linux.ibm.com, linkw@gcc.gnu.org, joseph@codesourcery.com,
 richard.sandiford@arm.com
Subject: Re: [PATCH] Fold (add -1; zero_ext;
 add +1) operations to zero_ext when not zero (PR37451, PR61837)
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On Wed, Apr 15, 2020 at 10:18:16AM +0100, Richard Sandiford wrote:
> luoxhu--- via Gcc-patches <gcc-patches@gcc.gnu.org> writes:
> > -    count = simplify_gen_binary (PLUS, mode, count, const1_rtx);
> > +    {
> > +      /* Fold (add -1; zero_ext; add +1) operations to zero_ext based on addop0
> > +	 is never zero, as gimple pass loop ch will do optimization to simplify
> > +	 the loop to NO loop for loop condition is false.  */
> 
> IMO the code needs to prove this, rather than just assume that previous
> passes have made it so.

Well, it should gcc_assert it, probably.

It is the left-hand side of a+b...  it cannot be 0, because niter always
is simplified!


Segher