Hi,
Using GNAT v11.2/0-4 for ARM (Alire), the following procedure Unbiased_Rounding for Float works as expected.

function Unbiased_Rounding (X : Float) return Float is
Y : Float;
begin
Asm (“vrintn.f32 %0,%1”,
Outputs => Float’asm_output (“=t”, Y),
Inputs => Float’asm_input (“t”, X));
return Y;
end Unbiased_Rounding;

according to Machine Constraints (Using the GNU Compiler Collection (GCC))
the constraint t means "VFP floating-point registers s0-s31. Used for 32 bit values” and the constraint w means "VFP floating-point registers d0-d31 and the appropriate subset d0-d15 based on command line options. Used for 64 bit values only”

therefore we wrote our long_float version as

function Unbiased_Rounding (X : Long_Float) return Long_Float is
Y : Long_Float;
begin
Asm (“vrintn.f64 %0,%1”,
Outputs => Long_Float’asm_output (“=w”, Y),
Inputs => Long_Float’asm_input (“w”, X));
return Y;
end Unbiased_Rounding;

however this fails to compile.
GNAT 11.2/0-4 (Alire) complains
Error: invalid instruction shape – `vrintn.f64 s14,s14’

presumably because the operands are S registers rather than double precisions D registers.
Is this a bug or have we misunderstood something?

Best wishes,
Ahlan

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