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Merge #84

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84: Remove unnecessary branch instruction in crt0 r=Lokathor a=ketsuban

I noticed a while ago that the BEQ instruction wasn't actually doing anything because I forgot the difference between SUB and SUBS (the latter sets condition flags). Moreover, I don't need a BEQ in the first place since ARM instructions are inherently conditional; it's not a huge deal, but it improves performance for this early code because the pipeline stays nice and full.

Co-authored-by: Thomas Winwood <twwinwood@gmail.com>
This commit is contained in:
bors[bot] 2019-06-04 20:56:49 +00:00
parent 038b887235 4d3a287c6b
commit f66ccba442
1 changed files with 7 additions and 7 deletions
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14
crt0.s
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@ -63,14 +63,14 @@ __start:
ldr r0, =__data_lma @ source address
ldr r1, =__data_start @ destination address
ldr r2, =__data_end
sub r2, r2, r1
beq .Lskip @ don't try to copy an empty .data section
add r2, #3
mov r2, r2, asr #2 @ length (in words)
add r2, #0x04000000 @ copy by words
swi 0xb0000
subs r2, r1 @ length
@ these instructions are only executed if r2 is nonzero
@ (i.e. don't bother copying an empty .data section)
addne r2, #3
asrne r2, #2
addne r2, #0x04000000
swine 0xb0000
.Lskip:
@ jump to user code
ldr r0, =main
bx r0