Re: [PATCH 1/3, ARM, libgcc, ping5] Code size optimization for the fmul/fdiv and dmul/ddiv function in libgcc

[Ramana Radhakrishnan <ramana dot gcc at googlemail dot com>]

On Thu, Nov 13, 2014 at 4:03 PM, Thomas Preud'homme
<thomas.preudhomme@arm.com> wrote:
> [Taking over Tony's patch]
>
> Ping?
>
> Best regards,
>
> Thomas
>
>> -----Original Message-----
>> From: gcc-patches-owner@gcc.gnu.org [mailto:gcc-patches-
>> owner@gcc.gnu.org] On Behalf Of Tony Wang
>> Sent: Thursday, August 21, 2014 7:15 AM
>> To: gcc-patches@gcc.gnu.org
>> Subject: [PATCH 1/3,ARM,libgcc]Code size optimization for the fmul/fdiv
>> and dmul/ddiv function in libgcc
>>
>> Hi there,
>>
>> In libgcc the file ieee754-sf.S and ieee754-df.S have some function pairs
>> which will be bundled into one .o
>> file and sharing the same .text section. For example, the fmul and fdiv,
>> the libgcc makefile will build them
>> into one .o file and archived into libgcc.a. So when user only call single
>> float point multiply functions, the
>> fdiv function will also be linked, and as fmul and fdiv share the same .text
>> section, linker option
>> --gc-sections or -flot can't remove the dead code.
>>
>> So this optimization just separates the function pair(fmul/fdiv and
>> dmul/ddiv) into different sections,
>> following the naming pattern of -ffunction-
>> sections(.text.__functionname), through which the unused sections
>> of fdiv/ddiv can be eliminated through option --gcc-sections when users
>> only use fmul/dmul.The solution is to
>> add a conditional statement in the macro FUNC_START, which will
>> conditional change the section of a function
>> from .text to .text.__\name. when compiling with the L_arm_muldivsf3
>> or L_arm_muldivdf3 macro.
>>
>> GCC regression test has been done on QEMU for Cortex-M3. No new
>> regressions when turn on this patch.
>>
>> The code reduction for thumb2 on cortex-m3 is:
>> 1. When user only use single float point multiply:
>> fmul+fdiv => fmul will have a code size reduction of 318 bytes.
>>
>> 2. When user only use double float point multiply:
>> dmul+ddiv => dmul will have a code size reduction of 474 bytes.
>>
>> Ok for trunk?

This is OK.


Ramana
>>
>> BR,
>> Tony
>>
>> Step 1: Provide another option: sp-scetion to control whether to split the
>> section of a function pair into two
>> part.
>>
>> gcc/libgcc/ChangeLog:
>> 2014-08-21  Tony Wang  <tony.wang@arm.com>
>>
>>         * config/arm/lib1funcs.S (FUNC_START): Add conditional section
>>         redefine for macro L_arm_muldivsf3 and L_arm_muldivdf3
>>         (SYM_END, ARM_SYM_START): Add macros used to expose function
>>         Symbols
>>
>> diff --git a/libgcc/config/arm/lib1funcs.S b/libgcc/config/arm/lib1funcs.S
>> index b617137..0f87111 100644
>> --- a/libgcc/config/arm/lib1funcs.S
>> +++ b/libgcc/config/arm/lib1funcs.S
>> @@ -418,8 +418,12 @@ SYM (\name):
>>  #define THUMB_SYNTAX
>>  #endif
>>
>> -.macro FUNC_START name
>> +.macro FUNC_START name sp_section=
>> +  .ifc \sp_section, function_section
>> +     .section        .text.__\name,"ax",%progbits
>> +  .else
>>       .text
>> +  .endif
>>       .globl SYM (__\name)
>>       TYPE (__\name)
>>       .align 0
>> @@ -429,14 +433,24 @@ SYM (\name):
>>  SYM (__\name):
>>  .endm
>>
>> +.macro ARM_SYM_START name
>> +       TYPE (\name)
>> +       .align 0
>> +SYM (\name):
>> +.endm
>> +
>> +.macro SYM_END name
>> +       SIZE (\name)
>> +.endm
>> +
>>  /* Special function that will always be coded in ARM assembly, even if
>>     in Thumb-only compilation.  */
>>
>>  #if defined(__thumb2__)
>>
>>  /* For Thumb-2 we build everything in thumb mode.  */
>> -.macro ARM_FUNC_START name
>> -       FUNC_START \name
>> +.macro ARM_FUNC_START name sp_section=
>> +       FUNC_START \name \sp_section
>>         .syntax unified
>>  .endm
>>  #define EQUIV .thumb_set
>> @@ -467,8 +481,12 @@ _L__\name:
>>  #ifdef __ARM_ARCH_6M__
>>  #define EQUIV .thumb_set
>>  #else
>> -.macro       ARM_FUNC_START name
>> +.macro       ARM_FUNC_START name sp_section=
>> +  .ifc \sp_section, function_section
>> +     .section        .text.__\name,"ax",%progbits
>> +  .else
>>       .text
>> +  .endif
>>       .globl SYM (__\name)
>>       TYPE (__\name)
>>       .align 0
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