https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87664
Bug ID: 87664
Summary: invariant in loop after optimization
Product: gcc
Version: 9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: drepper.fsp+rhbz at gmail dot com
Target Milestone: ---
Compile the following code with the current trunk or gcc 8.2.1:
#include <array>
#include <numeric>
int rs(int s) {
std::array<int,100> ar;
std::iota(ar.begin(), ar.end(), s);
return std::accumulate(ar.begin(), ar.end(), 0);
}
With -O2 this leads on x86-64 to the following code:
0000000000000000 <rs(int)>:
0: 48 81 ec 20 01 00 00 sub $0x120,%rsp
7: 48 8d 44 24 88 lea -0x78(%rsp),%rax
c: 0f 1f 40 00 nopl 0x0(%rax)
10: 89 38 mov %edi,(%rax)
12: 48 8d 8c 24 18 01 00 lea 0x118(%rsp),%rcx
19: 00
1a: 48 83 c0 04 add $0x4,%rax
1e: ff c7 inc %edi
20: 48 39 c8 cmp %rcx,%rax
23: 75 eb jne 10 <rs(int)+0x10>
25: 48 8d 54 24 88 lea -0x78(%rsp),%rdx
2a: 31 c0 xor %eax,%eax
2c: 0f 1f 40 00 nopl 0x0(%rax)
30: 03 02 add (%rdx),%eax
32: 48 8d b4 24 18 01 00 lea 0x118(%rsp),%rsi
39: 00
3a: 48 83 c2 04 add $0x4,%rdx
3e: 48 39 f2 cmp %rsi,%rdx
41: 75 ed jne 30 <rs(int)+0x30>
43: 48 81 c4 20 01 00 00 add $0x120,%rsp
4a: c3 retq
The relevant parts are the loop starting at offsets 10 and 30. The respective
lea instructions to compute the end address of the loop at offset 12 and 32 are
invariant and should be hoisted out of the loops.
