https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124339
Bug ID: 124339
Summary: ARM64 -O3 (ftree-vectorize) giant assembly with inc
inside the loop condition
Product: gcc
Version: 15.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: szuplak at gmail dot com
Target Milestone: ---
If we use the incrementation operator inside the loop condition,
for the ARM64 gcc 15 compiled with O3 (ftree-vectorize) generates 178 lines of
assembly (the example below.)
Compiled with -O2 or -O3 -f-no-tree-vectorize generates only 16 lines.
Looks normal on gcc 15 with x86-64 and MIPS64.
GCC 14 with ARM64 also creates normal assembly for ARM64 so looks like only v15
is affected.
Example - 178 lines of assembly
int foo(const char* s, int size)
{
while((*s++) && (--size > 0)) {
}
return size;
}
However If I move one of the operation to the loop body like that:
int foo(const char* s, int size)
{
while((*s) && (--size > 0)) {
s++;
}
return size;
}
The assembly is normal size
