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

Tony Wang tony.wang@arm.com
Fri Sep 26 02:11:00 GMT 2014


Ping?

> -----Original Message-----
> From: Tony Wang [mailto:tony.wang@arm.com]
> Sent: Tuesday, September 16, 2014 11:01 AM
> To: 'gcc-patches@gcc.gnu.org'
> Cc: Richard Earnshaw; Ramana Radhakrishnan
> Subject: RE: [PATCH 1/3,ARM,libgcc]Code size optimization for the fmul/fdiv and dmul/ddiv function in libgcc
> 
> Ping?
> 
> > -----Original Message-----
> > From: Tony Wang [mailto:tony.wang@arm.com]
> > Sent: Thursday, September 04, 2014 10:15 AM
> > To: 'gcc-patches@gcc.gnu.org'
> > Cc: Richard Earnshaw; Ramana Radhakrishnan
> > Subject: RE: [PATCH 1/3,ARM,libgcc]Code size optimization for the fmul/fdiv and dmul/ddiv function in
libgcc
> >
> > Ping 2?
> >
> > > -----Original Message-----
> > > From: Tony Wang [mailto:tony.wang@arm.com]
> > > Sent: Thursday, August 28, 2014 2:02 PM
> > > To: 'gcc-patches@gcc.gnu.org'
> > > Cc: Richard Earnshaw; Ramana Radhakrishnan
> > > Subject: RE: [PATCH 1/3,ARM,libgcc]Code size optimization for the fmul/fdiv and dmul/ddiv function in
libgcc
> > >
> > > Ping?
> > >
> > > > -----Original Message-----
> > > > From: Tony Wang [mailto:tony.wang@arm.com]
> > > > Sent: Thursday, August 21, 2014 2:15 PM
> > > > 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?
> > > >
> > > > 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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