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Re: Safe Identical Code Folding for X86-64.

From: Sriraman Tallam <tmsriram at google dot com>
To: John Reiser <jreiser at bitwagon dot com>
Cc: binutils at sourceware dot org
Date: Thu, 21 Jan 2010 17:25:53 -0800
Subject: Re: Safe Identical Code Folding for X86-64.
References: <863b0cbf1001211651u552ea814jbd53359443caae0@mail.gmail.com> <4B58FC6D.4030009@bitwagon.com>

On Thu, Jan 21, 2010 at 5:16 PM, John Reiser <jreiser@bitwagon.com> wrote:
> On 01/21/2010 04:51 PM, Sriraman Tallam wrote:
>
>> ? ? ?I am implementing a safe ICF option for gold ... for AMD X86-64. ...
>
>> Case (i) : For position dependent code (non-PIC), ?there is no
>> problem. A function call is always a PC relative relocation and a
>> function pointer is a direct relocation.
>
> That depends on the compiler. ?I have a compiler that uses no relocation
> at all for a CALL if the target is visible in the same compilation unit.
> The displacement is computed at compile time, and used as a constant.
> Also, in some cases a function pointer can be created by %rip-relative
> LEA using a constant displacement with no relocation at all.

Is it true even if you use -ffunction-sections ?

>
> Is the proposed ICF for gcc only? ?What are the assumptions
> about the properties of compiler-generated code?
>
> --
>

References:
- Safe Identical Code Folding for X86-64.
  - From: Sriraman Tallam
- Re: Safe Identical Code Folding for X86-64.
  - From: John Reiser

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