Carlo Kok via llvm-dev
2022-Jan-04 20:05 UTC
[llvm-dev] ASM disappears when NOT optimizing
When compiling:
; ModuleID = 'ExternalCalls-6069268ae2f83f7c993054596767686a'
source_filename = "ExternalCalls-6069268ae2f83f7c993054596767686a"
target datalayout =
"e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
target triple = "aarch64-linux-gnu"
define weak void @_start() #1 {
BasicBlock107:
call void asm "\0D\0A mov x29, #0x0\0D\0A mov x30,
#0x0\0D\0A mov x5, x0\0D\0A ldr x1, [sp]\0D\0A add x2, sp,
#0x8\0D\0A mov x6, sp\0D\0A adrp x0,
__elements_entry_point_helper\0D\0A add x0, x0,
:lo12:__elements_entry_point_helper\0D\0A adrp x3, __elements_init\0D\0A
add x3, x3, :lo12:__elements_init\0D\0A adrp x4, __elements_fini\0D\0A
add x4, x4, :lo12:__elements_fini\0D\0A bl __libc_start_main\0D\0A\0D\0A
", ""()
ret void
}
attributes #1 = { naked uwtable }
I get this in -O0 (with LLC)
_start: // @_start
ret
In O1/2/3 I get:
_start: // @_start
mov x29, #0
mov x30, #0
mov x5, x0
ldr x1, [sp]
add x2, sp, #8
mov x6, sp
adrp x0, __elements_entry_point_helper
add x0, x0, :lo12:__elements_entry_point_helper
adrp x3, __elements_init
add x3, x3, :lo12:__elements_init
adrp x4, __elements_fini
add x4, x4, :lo12:__elements_fini
bl __libc_start_main
ret
godbolt repro:
https://godbolt.org/z/MoMzE9Kha
Can anyone tell me what I'm doing wrong here?
--
Carlo Kok
Jacob Lifshay via llvm-dev
2022-Jan-04 20:56 UTC
[llvm-dev] ASM disappears when NOT optimizing
On Tue, Jan 4, 2022, 12:04 Carlo Kok via llvm-dev <llvm-dev at lists.llvm.org> wrote:> > BasicBlock107: > call void asm "\0D\0A mov x29, #0x0\0D\0A >you forgot to add sideeffect to the asm -- because you told it it has no outputs, and doesn't affect anything else (no sideeffect), llvm decided to omit it. Jacob>-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20220104/d478232f/attachment.html>