https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67681
Bug ID: 67681
Summary: Missed vectorization: induction variable used after
loop
Product: gcc
Version: 6.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: alalaw01 at gcc dot gnu.org
Target Milestone: ---
The inner loop here:
void addlog2 (int *data)
{
int i = 1;
for (int j=0; j<=30; j++) {
int max = 1 << j;
if (FOO && i>max) break;
for (; i <= max; i++)
data[i] += j;
}
}
does not vectorize if the if(FOO...) is present:
$ /work/alalaw01/build-aarch64-none-elf/install/bin/aarch64-none-elf-gcc -S -O2
-ftree-vectorize -fdump-tree-vect-details=stdout loop9b.c -DFOO=1 | grep
vectorized
loop9b.c:1:6: note: not vectorized: inner-loop count not invariant.
loop9b.c:8:5: note: === vect_mark_stmts_to_be_vectorized ===
loop9b.c:8:5: note: not vectorized: value used after loop.
loop9b.c:8:5: note: === vect_mark_stmts_to_be_vectorized ===
loop9b.c:8:5: note: not vectorized: value used after loop.
loop9b.c:1:6: note: vectorized 0 loops in function.
$ aarch64-none-elf-gcc -S -O2 -ftree-vectorize -fdump-tree-vect-details=stdout
loop9b.c -DFOO=0 | grep vectorized
loop9b.c:4:3: note: not vectorized: inner-loop count not invariant.
loop9b.c:8:5: note: === vect_mark_stmts_to_be_vectorized ===
loop9b.c:8:5: note: loop vectorized
loop9b.c:1:6: note: vectorized 1 loops in function.
Same with -O3. Of course clever analysis could figure out that i>max is never
true, but even without that, we should be able to get 'i' back afterwards.
