I am not certain based on below code if the call to usub64_borrow() is inlined or not - but seems like it is. Maybe you can help confirm on that. FYI - I have marked the function as non-static and non-inline in fpu/softfloat.c. In the same file, there are calls to this function and this is how disassembly looks like in Good and Bad case
Good case
Code:
; a0 = a0 >> c;
188c8: 6b 25 ca 9a lsr x11, x11, x10
; a->frac_lo = a1 | (sticky != 0);
188cc: 1f 01 00 f1 cmp x8, #0
188d0: e8 07 9f 1a cset w8, ne
188d4: 28 01 08 aa orr x8, x9, x8
188d8: 2b a0 00 a9 stp x11, x8, [x1, #8]
; r->frac_lo = usub64_borrow(a->frac_lo, b->frac_lo, &c);
188dc: 09 08 40 f9 ldr x9, [x0, #16]
; volatile unsigned long long b = *pborrow;
188e0: ff 07 00 f9 str xzr, [sp, #8]
; x = __builtin_subcll(x, y, b, (uint64_t*)&b);
188e4: ea 07 40 f9 ldr x10, [sp, #8]
188e8: 28 01 08 eb subs x8, x9, x8
188ec: e9 27 9f 1a cset w9, lo
188f0: 08 01 0a eb subs x8, x8, x10
188f4: ea 27 9f 1a cset w10, lo
188f8: 29 01 0a 2a orr w9, w9, w10
188fc: e9 07 00 f9 str x9, [sp, #8]
; *pborrow = b & 1;
18900: e9 07 40 f9 ldr x9, [sp, #8]
18904: 29 01 40 92 and x9, x9, #0x1
; r->frac_lo = usub64_borrow(a->frac_lo, b->frac_lo, &c);
18908: 08 08 00 f9 str x8, [x0, #16]
; r->frac_hi = usub64_borrow(a->frac_hi, b->frac_hi, &c);
1890c: 0a 04 40 f9 ldr x10, [x0, #8]
18910: 2b 04 40 f9 ldr x11, [x1, #8]
; volatile unsigned long long b = *pborrow;
18914: e9 07 00 f9 str x9, [sp, #8]
; x = __builtin_subcll(x, y, b, (uint64_t*)&b);
18918: e9 07 40 f9 ldr x9, [sp, #8]
1891c: 4a 01 0b eb subs x10, x10, x11
18920: eb 27 9f 1a cset w11, lo
18924: 49 01 09 eb subs x9, x10, x9
18928: ea 27 9f 1a cset w10, lo
1892c: 6a 01 0a 2a orr w10, w11, w10
18930: ea 07 00 f9 str x10, [sp, #8]
18934: ea 07 40 f9 ldr x10, [sp, #8]
18938: 09 04 00 f9 str x9, [x0, #8]
; if (a->frac_hi) {
Bad case
Code:
; a0 = a0 >> c;
17ebc: 6b 25 ca 9a lsr x11, x11, x10
; a->frac_lo = a1 | (sticky != 0);
17ec0: 1f 01 00 f1 cmp x8, #0
17ec4: e8 07 9f 1a cset w8, ne
17ec8: 28 01 08 aa orr x8, x9, x8
17ecc: 2b a0 00 a9 stp x11, x8, [x1, #8]
; r->frac_lo = usub64_borrow(a->frac_lo, b->frac_lo, &c);
17ed0: 0a a4 40 a9 ldp x10, x9, [x0, #8]
; x = __builtin_subcll(x, y, b, &b);
17ed4: 28 01 08 eb subs x8, x9, x8
17ed8: e9 27 9f 1a cset w9, lo
; r->frac_lo = usub64_borrow(a->frac_lo, b->frac_lo, &c);
17edc: 08 08 00 f9 str x8, [x0, #16]
; r->frac_hi = usub64_borrow(a->frac_hi, b->frac_hi, &c);
17ee0: 2b 04 40 f9 ldr x11, [x1, #8]
; x = __builtin_subcll(x, y, b, &b);
17ee4: 4a 01 0b cb sub x10, x10, x11
17ee8: 49 01 09 cb sub x9, x10, x9
17eec: 09 04 00 f9 str x9, [x0, #8]
; if (a->frac_hi) {
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