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firmware: fw_base: Optimize _hartid_to_scratch() implementation

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This patch optimizes _hartid_to_scratch() in following ways:
1. Use caller saved registers instead of callee saved registers
   so that we don't need to save/restore registers on stack
2. Remove second redundant mul instruction by re-arranging
   instructions

Overall, we reduce 9 instructions in _hartid_to_scratch()
implementation.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Atish Patra <atish.patra@wdc.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
This commit is contained in:
Anup Patel
2020-03-11 19:25:24 +05:30
committed by Anup Patel
parent f92147c2b2
commit eeae3d9582
1 changed files with 14 additions and 23 deletions
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37
firmware/fw_base.S
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@@ -409,35 +409,26 @@ _link_end:
.align 3
.globl _hartid_to_scratch
_hartid_to_scratch:
add sp, sp, -(3 * __SIZEOF_POINTER__)
REG_S s0, (sp)
REG_S s1, (__SIZEOF_POINTER__)(sp)
REG_S s2, (__SIZEOF_POINTER__ * 2)(sp)
/*
* a0 -> HART ID (passed by caller)
* s0 -> HART Stack Size
* s1 -> HART Stack End
* s2 -> Temporary
* t0 -> HART Stack Size
* t1 -> HART Stack End
* t2 -> Temporary
*/
la s2, platform
la t2, platform
#if __riscv_xlen == 64
lwu s0, SBI_PLATFORM_HART_STACK_SIZE_OFFSET(s2)
lwu s2, SBI_PLATFORM_HART_COUNT_OFFSET(s2)
lwu t0, SBI_PLATFORM_HART_STACK_SIZE_OFFSET(t2)
lwu t2, SBI_PLATFORM_HART_COUNT_OFFSET(t2)
#else
lw s0, SBI_PLATFORM_HART_STACK_SIZE_OFFSET(s2)
lw s2, SBI_PLATFORM_HART_COUNT_OFFSET(s2)
lw t0, SBI_PLATFORM_HART_STACK_SIZE_OFFSET(t2)
lw t2, SBI_PLATFORM_HART_COUNT_OFFSET(t2)
#endif
mul s2, s2, s0
la s1, _fw_end
add s1, s1, s2
mul s2, s0, a0
sub s1, s1, s2
li s2, SBI_SCRATCH_SIZE
sub a0, s1, s2
REG_L s0, (sp)
REG_L s1, (__SIZEOF_POINTER__)(sp)
REG_L s2, (__SIZEOF_POINTER__ * 2)(sp)
add sp, sp, (3 * __SIZEOF_POINTER__)
sub t2, t2, a0
mul t2, t2, t0
la t1, _fw_end
add t1, t1, t2
li t2, SBI_SCRATCH_SIZE
sub a0, t1, t2
ret
.section .entry, "ax", %progbits