Graphics on BangleJS2

The Pico code is for a Cortex M0+ and what you have in your snippet is incomplete.
The correct code for a Cortex M4 is this (from assembled+disassembled libgcc, corrected to return the result in S0 instead of R0, since the compiler ignores the softfp ABI for functions in the same compilation unit, apparently):

let c = E.compiledC(`
// int boop(double)

extern "C" float __attribute__((naked)) d2f(double) {__asm__ volatile(R"(
 	mov.w	r2, r1, lsl 1
 	subs.w	r3, r2, 0x70000000
 	itt	cs
 	subscs.w ip, r3, 0x200000
 	rsbscs	ip, ip, 0x1fc00000
 	bls.n	2f
1:
 	and.w	ip, r1, 0x80000000
 	mov.w	r2, r0, lsl 3
 	orr.w	r0, ip, r0, lsr 29
 	cmp.w	r2, 0x80000000
 	adc.w	r0, r0, r3, lsl 2
 	it	eq
 	biceq.w	r0, r0, 1
 	b 6f
2:
 	tst.w	r1, 0x40000000
 	bne.n	3f
 	adds.w	r2, r3, 0x2e00000
 	itt	lt
 	andlt.w	r0, r1, 0x80000000
 	blt	6f
 	orr.w	r1, r1, 0x100000
 	mov.w	r2, r2, lsr 21
 	rsb	r2, r2, 24
 	rsb	ip, r2, 32
 	lsls.w	r3, r0, ip
 	lsr.w	r0, r0, r2
 	it	ne
 	orrne.w	r0, r0, 1
 	mov.w	r3, r1, lsl 11
 	mov.w	r3, r3, lsr 11
 	lsl.w	ip, r3, ip
 	orr.w	r0, r0, ip
 	lsr.w	r3, r3, r2
 	mov.w	r3, r3, lsl 1
 	b.n	1b
3:
 	mvns.w	r3, r2, asr 21
 	bne.n	5f
 	orrs.w	r3, r0, r1, lsl 12
 	ittt	ne
 	movne.w	r0, 0x7f000000
 	orrne.w	r0, r0, 0xc00000
 	bne	6f
5:
 	and.w	r0, r1, 0x80000000
 	orr.w	r0, r0, 0x7f000000
 	orr.w	r0, r0, 0x800000
6:
  vmov s0, r0
 	bx	lr
 	nop
)");}


int boop(double d) {
  return d2f(d) * 3;
}
`);

print('boop:', c.boop(3.5)); // 3.5 * 3 = 10.5 cast to int = 10

Note that you have to call the function explicitly, I couldn't use a float cast and get it to link as __aeabi_d2f. It might work if we compile the assembly into a library and then link to that. If one were to go that far, might as well link to libgcc and let the linker throw away all the stuff that isn't used.