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RE: GCC Compiler Optimization ignores or mistreats MFENCE memory barrier related instruction

From: Vivek Kinhekar <vivek dot kinhekar at blackfigtech dot com>
To: Alexander Monakov <amonakov at ispras dot ru>
Cc: "gcc at gcc dot gnu dot org" <gcc at gcc dot gnu dot org>
Date: Fri, 13 Apr 2018 12:34:30 +0000
Subject: RE: GCC Compiler Optimization ignores or mistreats MFENCE memory barrier related instruction
References: <MAXPR0101MB12283F94DB8FDBD9F8969199F0B30@MAXPR0101MB1228.INDPRD01.PROD.OUTLOOK.COM> <alpine.LNX.2.20.13.1804131526260.29823@monopod.intra.ispras.ru>
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Thanks for the quick response, Alexander!

Regards,
Vivek Kinhekar
+91-7709046470

-----Original Message-----
From: Alexander Monakov <amonakov@ispras.ru> 
Sent: Friday, April 13, 2018 5:58 PM
To: Vivek Kinhekar <vivek.kinhekar@blackfigtech.com>
Cc: gcc@gcc.gnu.org
Subject: Re: GCC Compiler Optimization ignores or mistreats MFENCE memory barrier related instruction

On Fri, 13 Apr 2018, Vivek Kinhekar wrote:
> The mfence instruction with memory clobber asm instruction should 
> create a barrier between division and printf instructions.

No, floating-point division does not touch memory, so the asm does not (and need not) restrict its motion.

Alexander

References:
- GCC Compiler Optimization ignores or mistreats MFENCE memory barrier related instruction
  - From: Vivek Kinhekar
- Re: GCC Compiler Optimization ignores or mistreats MFENCE memory barrier related instruction
  - From: Alexander Monakov

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