https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78182
Bug ID: 78182
Summary: Missed optimizations: "fused" byte stores
Product: gcc
Version: 7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: rureclonic at thraml dot com
Target Milestone: ---
Consider the following program, which writes '000000000001' in `text`.
constexpr unsigned long Size = 12;
char text[Size];
void foo() {
auto value = 1u;
for (auto i = 0ul; i < Size; ++i) {
text[Size - i - 1] = (value % 10) + '0';
value /= 10;
}
}
The codegen for foo with `g++-7 -std=c++1z -O3 -march=corei7-avx` is:
foo():
mov BYTE PTR text[rip+11], 49
mov BYTE PTR text[rip+10], 48
mov BYTE PTR text[rip+9], 48
mov BYTE PTR text[rip+8], 48
mov BYTE PTR text[rip+7], 48
mov BYTE PTR text[rip+6], 48
mov BYTE PTR text[rip+5], 48
mov BYTE PTR text[rip+4], 48
mov BYTE PTR text[rip+3], 48
mov BYTE PTR text[rip+2], 48
mov BYTE PTR text[rip+1], 48
mov BYTE PTR text[rip], 48
ret
Why can't the 9 last movs be combined into wider stores?
