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[Bug tree-optimization/85366] Failure to use both div and mod results of one IDIV in a prime-factor loop while(n%i==0) { n/=i; }
- From: "pinskia at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Sun, 15 Apr 2018 06:02:02 +0000
- Subject: [Bug tree-optimization/85366] Failure to use both div and mod results of one IDIV in a prime-factor loop while(n%i==0) { n/=i; }
- Auto-submitted: auto-generated
- References: <bug-85366-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85366
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
For arm64, it is obvious why it is not optimized into one divide:
.L2:
udiv w2, w0, w3
msub w2, w2, w3, w0
cbnz w2, .L5
sdiv w2, w0, w3
.p2align 2
.L4:
mov w0, w2
str w3, [x1], 4
sdiv w2, w2, w3
msub w4, w2, w3, w0
cbz w4, .L4
.L5:
add w3, w3, 1
cmp w3, w0
ble .L2
.L1:
ret
--- CUT ---
In the first case we have an unsigned division while in the second case we have
a signed division.