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Re: [RFA] [PowerPC]

From: edmar <edmar at freescale dot com>
To: Segher Boessenkool <segher at kernel dot crashing dot org>
Cc: <gcc-patches at gcc dot gnu dot org>
Date: Thu, 21 Apr 2011 10:27:47 -0500
Subject: Re: [RFA] [PowerPC]
References: <4DADD4DC.4040305@freescale.com> <3c72f77b4a6d6d83bd061d725ee96d2f@kernel.crashing.org>

On 04/20/2011 07:52 PM, Segher Boessenkool wrote:

The test and-1.c has wrong logic.
In the formula:
y & ~(y & -y)
The part (y & -y) is always a mask with one bit set, which corresponds
to the least significant "1" bit in y.
The final result is that bit, is set to zero (y & ~mask)
There is no boolean simplification possible, and the compiler always produces a nand instruction.
The formula is equal to y & (y-1) , maybe the testcase is testing that?

Segher

Ah, yes
A neg/nand/and should be optimized into a sub -1/and.

I will check why this is not happening.

Thanks
Edmar

References:
- [RFA] [PowerPC]
  - From: edmar
- Re: [RFA] [PowerPC]
  - From: Segher Boessenkool

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