I would like to realize if condition in armv8 NEON inline assembly code. In armv7 this was possible through checking overflow bit like this:
VMRS r4, FPSCR
BIC r4, r4, #(1<<27)
VMSR FPSCR, r4
vtst.16 d30, d30, d30
vqadd.u16 d30, d30, d30
vmrs r4, FPSCR
tst r4, #(1<<27)
bne label1
But I am not able to achieve this in armv8 equivalent code. It seems that SQADD doesnt affect overflow bit in FPSR or I cannot check it like this. Is it possible or is there better approach how to skip long part of code?
Thank you
All ARMv8-based devices support Neon. Do we need to explicitly say -mattr=+neon for ARMv8 devices?
vfpv4 implies add VFPv4 instructions which for me is scalar FMA instructions. neon implies add Neon instructions which to me refers to the original Advanced SIMD / Neon instructions as per the original Armv7-A instruction set. neon-vfpv4 implies add Neon instructions which came in with the Neon unit that came in with VFPv4.
On AArch32 which has instructions in the 32 bit world for both A32 and T32 ISAs, you would need to put -mattr=+neon to ensure that Neon is generated as the defaults could well be conservative and there are options to have devices without FP or SIMD though that’s a bit rare in the Android world these days.
Most popular TVM target line for ARMv7 Android phones is probably: More TVM target lines for other Android architectures is here Pedantically speaking, there is no armv7 , it’s either armv7-a or armv7ve.
The same information is available in Aarch64. You just need to replace:
VMSR r4, FPSCR
VMRS FPSCR, r4
by:
MRS w4, FPSR
MSR FPSR, w4
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