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Re: Mysterious decision in combine
- From: Richard Henderson <rth at redhat dot com>
- To: vogt at linux dot vnet dot ibm dot com, gcc at gcc dot gnu dot org
- Date: Thu, 17 Mar 2016 13:22:04 -0700
- Subject: Re: Mysterious decision in combine
- Authentication-results: sourceware.org; auth=none
- References: <20160317063531 dot GA5065 at linux dot vnet dot ibm dot com>
On 03/16/2016 11:35 PM, Dominik Vogt wrote:
> How does combine get this idea (it's the only match in the
> function)?
>
> Trying 7 -> 12:
> Successfully matched this instruction:
> (set (reg/i:DI 2 %r2)
> (and:DI (subreg:DI (reg:SI 64) 0)
> (const_int 4294901775 [0xffff000f])))
> allowing combination of insns 7 and 12
>From the recorded nonzero_bits.
> (Eventually the two "and"s with constant values
> are not merged into a single "and" with a single constant.)
That's a concern...
r~