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 the 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.
There are 3 parts: mul, div and common. This patch puts mul and common
together, so that user's multiply won't pull-in div, butuser's div
will still pull-in mul. It is reasonable because size of mul is far
smaller than size of div.
ChangLog changes are:
***gcc/libgcc/ChangeLog***
2014-05-28 Tony Wang <tony.w...@arm.com>
* config/arm/lib1funcs.S (FUNC_START): Add conditional section
redefine for macro L_arm_muldivsf3 and L_arm_muldivdf3
Bootstrapped on x86_64-linux-gnu and no regression found in the
testsuite. Patch is in attachment.
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.
BR,
Tony
diff --git a/libgcc/config/arm/lib1funcs.S b/libgcc/config/arm/lib1funcs.S
index b617137..0454bc8 100644
--- a/libgcc/config/arm/lib1funcs.S
+++ b/libgcc/config/arm/lib1funcs.S
@@ -419,7 +419,11 @@ SYM (\name):
#endif
.macro FUNC_START name
+#if defined (L_arm_muldivsf3) || defined (L_arm_muldivdf3)
+ .section .text.__\name,"ax",%progbits
+#else
.text
+#endif
.globl SYM (__\name)
TYPE (__\name)
.align 0
@@ -468,7 +472,11 @@ _L__\name:
#define EQUIV .thumb_set
#else
.macro ARM_FUNC_START name
+#if defined (L_arm_muldivsf3) || defined (L_arm_muldivdf3)
+ .section .text.__\name,"ax",%progbits
+#else
.text
+#endif
.globl SYM (__\name)
TYPE (__\name)
.align 0
