| Message ID | CAK=A3=33JChF2hpKEhSDcEpYwvoO5y-cLJC9T-TNERJZMUJF9g@mail.gmail.com |
|---|---|
| State | New |
| Headers | show |
Any comment on this patch? thanks, Cong On Thu, Oct 3, 2013 at 3:59 PM, Cong Hou <congh@google.com> wrote: > During loop versioning in vectorization, the alias check guarantees > that any load of a data reference with zero-step is a loop invariant, > which can be hoisted outside of the loop. After hoisting the load > statement, there may exist more loop invariant statements. This patch > tries to find all those statements and hoists them before the loop. > > An example is shown below: > > > for (i = 0; i < N; ++i) > a[i] = *b + 1; > > > After loop versioning the loop to be vectorized is guarded by > > if (b + 1 < a && a + N < b) > > which means there is no aliasing between *b and a[i]. The GIMPLE code > of the loop body is: > > <bb 5>: > # i_18 = PHI <0(4), i_29(6)> > # ivtmp_22 = PHI <10000(4), ivtmp_30(6)> > _23 = (long unsigned int) i_18; > _24 = _23 * 4; > _25 = a_6(D) + _24; > _26 = *b_8(D); =====> loop invariant > _27 = _26 + 1; =====> loop invariant > *_25 = _27; > i_29 = i_18 + 1; > ivtmp_30 = ivtmp_22 - 1; > if (ivtmp_30 != 0) > goto <bb 6>; > else > goto <bb 21>; > > > After hoisting loop invariant statements: > > > _26 = *b_8(D); > _27 = _26 + 1; > > <bb 5>: > # i_18 = PHI <0(4), i_29(6)> > # ivtmp_22 = PHI <10000(4), ivtmp_30(6)> > _23 = (long unsigned int) i_18; > _24 = _23 * 4; > _25 = a_6(D) + _24; > *_25 = _27; > i_29 = i_18 + 1; > ivtmp_30 = ivtmp_22 - 1; > if (ivtmp_30 != 0) > goto <bb 6>; > else > goto <bb 21>; > > > This patch is related to the bug report > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58508 > > > thanks, > Cong
On 10/14/13 17:31, Cong Hou wrote:
> Any comment on this patch?
Richi replied in the BZ you opened.
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58508
Essentially he said emit the load on the edge rather than in the block
itself.
jeff
diff --git gcc/testsuite/gcc.dg/vect/pr58508.c gcc/testsuite/gcc.dg/vect/pr58508.c new file mode 100644 index 0000000..cb22b50 --- /dev/null +++ gcc/testsuite/gcc.dg/vect/pr58508.c @@ -0,0 +1,20 @@ +/* { dg-do compile } */ +/* { dg-options "-O2 -ftree-vectorize -fdump-tree-vect-details" } */ + + +/* The GCC vectorizer generates loop versioning for the following loop + since there may exist aliasing between A and B. The predicate checks + if A may alias with B across all iterations. Then for the loop in + the true body, we can assert that *B is a loop invariant so that + we can hoist the load of *B before the loop body. */ + +void foo (int* a, int* b) +{ + int i; + for (i = 0; i < 100000; ++i) + a[i] = *b + 1; +} + + +/* { dg-final { scan-tree-dump-times "hoist" 2 "vect" } } */ +/* { dg-final { cleanup-tree-dump "vect" } } */
During loop versioning in vectorization, the alias check guarantees that any load of a data reference with zero-step is a loop invariant, which can be hoisted outside of the loop. After hoisting the load statement, there may exist more loop invariant statements. This patch tries to find all those statements and hoists them before the loop. An example is shown below: for (i = 0; i < N; ++i) a[i] = *b + 1; After loop versioning the loop to be vectorized is guarded by if (b + 1 < a && a + N < b) which means there is no aliasing between *b and a[i]. The GIMPLE code of the loop body is: <bb 5>: # i_18 = PHI <0(4), i_29(6)> # ivtmp_22 = PHI <10000(4), ivtmp_30(6)> _23 = (long unsigned int) i_18; _24 = _23 * 4; _25 = a_6(D) + _24; _26 = *b_8(D); =====> loop invariant _27 = _26 + 1; =====> loop invariant *_25 = _27; i_29 = i_18 + 1; ivtmp_30 = ivtmp_22 - 1; if (ivtmp_30 != 0) goto <bb 6>; else goto <bb 21>; After hoisting loop invariant statements: _26 = *b_8(D); _27 = _26 + 1; <bb 5>: # i_18 = PHI <0(4), i_29(6)> # ivtmp_22 = PHI <10000(4), ivtmp_30(6)> _23 = (long unsigned int) i_18; _24 = _23 * 4; _25 = a_6(D) + _24; *_25 = _27; i_29 = i_18 + 1; ivtmp_30 = ivtmp_22 - 1; if (ivtmp_30 != 0) goto <bb 6>; else goto <bb 21>; This patch is related to the bug report http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58508 thanks, Cong