| 2012-05-31 07:47:25 |
Ramana Radhakrishnan |
description |
Test case is reduced from CINT2000/175.vpr/util.c:free_chunk_memory(), and compile it with GCC FSF trunk,
$ arm-none-linux-gnueabi-gcc --version
arm-none-linux-gnueabi-gcc (GCC) 4.6.0 20100902 (experimental)
Copyright (C) 2010 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
$ arm-none-linux-gnueabi-gcc -march=armv7-a -mthumb -Os -O3 -mcpu=cortex-a9 -S extra_ldr_mov.c
GCC generates code like this,
free_chunk_memory:
@ args = 0, pretend = 0, frame = 0
@ frame_needed = 0, uses_anonymous_args = 0
push {r3, r4, r5, lr}
cbz r0, .L1
mov r4, r0
b .L3
.L4:
mov r4, r5 // <---[2]
.L3:
ldr r0, [r4, #0]
bl free
ldr r5, [r4, #4] // <---[1]
mov r0, r4 // <--- [3]
bl free
cmp r5, #0
bne .L4
We can exchange instruction [1] and [3], and change instruction [1] to 'ldr r4, [r4, #4]', then instruction [2] can be removed. |
Test case is reduced from CINT2000/175.vpr/util.c:free_chunk_memory(), and compile it with GCC FSF trunk,
$ arm-none-linux-gnueabi-gcc --version
arm-none-linux-gnueabi-gcc (GCC) 4.6.0 20100902 (experimental)
Copyright (C) 2010 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
$ arm-none-linux-gnueabi-gcc -march=armv7-a -mthumb -Os -O3 -mcpu=cortex-a9 -S extra_ldr_mov.c
GCC generates code like this,
free_chunk_memory:
@ args = 0, pretend = 0, frame = 0
@ frame_needed = 0, uses_anonymous_args = 0
push {r3, r4, r5, lr}
cbz r0, .L1
mov r4, r0
b .L3
.L4:
mov r4, r5 // <---[2]
.L3:
ldr r0, [r4, #0]
bl free
ldr r5, [r4, #4] // <---[1]
mov r0, r4 // <--- [3]
bl free
cmp r5, #0
bne .L4
We can exchange instruction [1] and [3], and change instruction [1] to 'ldr r4, [r4, #4]', then instruction [2] can be removed. |
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