On Wed, May 15, 2024 at 5:24 PM Richard Biener
<richard.guent...@gmail.com> wrote:
>
> On Wed, May 15, 2024 at 4:15 AM Hongtao Liu <crazy...@gmail.com> wrote:
> >
> > On Mon, May 13, 2024 at 3:40 PM Richard Biener
> > <richard.guent...@gmail.com> wrote:
> > >
> > > On Mon, May 13, 2024 at 4:29 AM liuhongt <hongtao....@intel.com> wrote:
> > > >
> > > > As testcase in the PR, O3 cunrolli may prevent vectorization for the
> > > > innermost loop and increase register pressure.
> > > > The patch removes the 1/3 reduction of unr_insn for innermost loop for
> > > > UL_ALL.
> > > > ul != UR_ALL is needed since some small loop complete unrolling at O2
> > > > relies
> > > > the reduction.
> > > >
> > > > Bootstrapped and regtested on x86_64-pc-linux-gnu{-m32,}.
> > > > No big impact for SPEC2017.
> > > > Ok for trunk?
> > >
> > > This removes the 1/3 reduction when unrolling a loop nest (the case I was
> > > concerned about). Unrolling of a nest is by iterating in
> > > tree_unroll_loops_completely
> > > so the to be unrolled loop appears innermost. So I think you need a new
> > > parameter on tree_unroll_loops_completely_1 indicating whether we're in
> > > the
> > > first iteration (or whether to assume inner most loops will "simplify").
> > yes, it would be better.
> > >
> > > Few comments below
> > >
> > > > gcc/ChangeLog:
> > > >
> > > > PR tree-optimization/112325
> > > > * tree-ssa-loop-ivcanon.cc (estimated_unrolled_size): Add 2
> > > > new parameters: loop and ul, and remove unr_insns reduction
> > > > for innermost loop.
> > > > (try_unroll_loop_completely): Pass loop and ul to
> > > > estimated_unrolled_size.
> > > >
> > > > gcc/testsuite/ChangeLog:
> > > >
> > > > * gcc.dg/tree-ssa/pr112325.c: New test.
> > > > * gcc.dg/vect/pr69783.c: Add extra option --param
> > > > max-completely-peeled-insns=300.
> > > > ---
> > > > gcc/testsuite/gcc.dg/tree-ssa/pr112325.c | 57 ++++++++++++++++++++++++
> > > > gcc/testsuite/gcc.dg/vect/pr69783.c | 2 +-
> > > > gcc/tree-ssa-loop-ivcanon.cc | 16 +++++--
> > > > 3 files changed, 71 insertions(+), 4 deletions(-)
> > > > create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr112325.c
> > > >
> > > > diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr112325.c
> > > > b/gcc/testsuite/gcc.dg/tree-ssa/pr112325.c
> > > > new file mode 100644
> > > > index 00000000000..14208b3e7f8
> > > > --- /dev/null
> > > > +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr112325.c
> > > > @@ -0,0 +1,57 @@
> > > > +/* { dg-do compile } */
> > > > +/* { dg-options "-O2 -fdump-tree-cunrolli-details" } */
> > > > +
> > > > +typedef unsigned short ggml_fp16_t;
> > > > +static float table_f32_f16[1 << 16];
> > > > +
> > > > +inline static float ggml_lookup_fp16_to_fp32(ggml_fp16_t f) {
> > > > + unsigned short s;
> > > > + __builtin_memcpy(&s, &f, sizeof(unsigned short));
> > > > + return table_f32_f16[s];
> > > > +}
> > > > +
> > > > +typedef struct {
> > > > + ggml_fp16_t d;
> > > > + ggml_fp16_t m;
> > > > + unsigned char qh[4];
> > > > + unsigned char qs[32 / 2];
> > > > +} block_q5_1;
> > > > +
> > > > +typedef struct {
> > > > + float d;
> > > > + float s;
> > > > + char qs[32];
> > > > +} block_q8_1;
> > > > +
> > > > +void ggml_vec_dot_q5_1_q8_1(const int n, float * restrict s, const
> > > > void * restrict vx, const void * restrict vy) {
> > > > + const int qk = 32;
> > > > + const int nb = n / qk;
> > > > +
> > > > + const block_q5_1 * restrict x = vx;
> > > > + const block_q8_1 * restrict y = vy;
> > > > +
> > > > + float sumf = 0.0;
> > > > +
> > > > + for (int i = 0; i < nb; i++) {
> > > > + unsigned qh;
> > > > + __builtin_memcpy(&qh, x[i].qh, sizeof(qh));
> > > > +
> > > > + int sumi = 0;
> > > > +
> > > > + for (int j = 0; j < qk/2; ++j) {
> > > > + const unsigned char xh_0 = ((qh >> (j + 0)) << 4) & 0x10;
> > > > + const unsigned char xh_1 = ((qh >> (j + 12)) ) & 0x10;
> > > > +
> > > > + const int x0 = (x[i].qs[j] & 0xF) | xh_0;
> > > > + const int x1 = (x[i].qs[j] >> 4) | xh_1;
> > > > +
> > > > + sumi += (x0 * y[i].qs[j]) + (x1 * y[i].qs[j + qk/2]);
> > > > + }
> > > > +
> > > > + sumf += (ggml_lookup_fp16_to_fp32(x[i].d)*y[i].d)*sumi +
> > > > ggml_lookup_fp16_to_fp32(x[i].m)*y[i].s;
> > > > + }
> > > > +
> > > > + *s = sumf;
> > > > +}
> > > > +
> > > > +/* { dg-final { scan-tree-dump {(?n)Not unrolling loop [1-9] \(--param
> > > > max-completely-peel-times limit reached} "cunrolli"} } */
> > > > diff --git a/gcc/testsuite/gcc.dg/vect/pr69783.c
> > > > b/gcc/testsuite/gcc.dg/vect/pr69783.c
> > > > index 5df95d0ce4e..a1f75514d72 100644
> > > > --- a/gcc/testsuite/gcc.dg/vect/pr69783.c
> > > > +++ b/gcc/testsuite/gcc.dg/vect/pr69783.c
> > > > @@ -1,6 +1,6 @@
> > > > /* { dg-do compile } */
> > > > /* { dg-require-effective-target vect_float } */
> > > > -/* { dg-additional-options "-Ofast -funroll-loops" } */
> > > > +/* { dg-additional-options "-Ofast -funroll-loops --param
> > > > max-completely-peeled-insns=300" } */
> > >
> > > If we rely on unrolling of a loop can you put #pragma unroll [N]
> > > before the respective loop
> > > instead?
> > >
> > > > #define NXX 516
> > > > #define NYY 516
> > > > diff --git a/gcc/tree-ssa-loop-ivcanon.cc b/gcc/tree-ssa-loop-ivcanon.cc
> > > > index bf017137260..5e0eca647a1 100644
> > > > --- a/gcc/tree-ssa-loop-ivcanon.cc
> > > > +++ b/gcc/tree-ssa-loop-ivcanon.cc
> > > > @@ -444,7 +444,9 @@ tree_estimate_loop_size (class loop *loop, edge
> > > > exit, edge edge_to_cancel,
> > > >
> > > > static unsigned HOST_WIDE_INT
> > > > estimated_unrolled_size (struct loop_size *size,
> > > > - unsigned HOST_WIDE_INT nunroll)
> > > > + unsigned HOST_WIDE_INT nunroll,
> > > > + enum unroll_level ul,
> > > > + class loop* loop)
> > > > {
> > > > HOST_WIDE_INT unr_insns = ((nunroll)
> > > > * (HOST_WIDE_INT) (size->overall
> > > > @@ -453,7 +455,15 @@ estimated_unrolled_size (struct loop_size *size,
> > > > unr_insns = 0;
> > > > unr_insns += size->last_iteration -
> > > > size->last_iteration_eliminated_by_peeling;
> > > >
> > > > - unr_insns = unr_insns * 2 / 3;
> > > > + /* For innermost loop, loop body is not likely to be simplied as
> > > > much as 1/3.
> > > > + and may increase a lot of register pressure.
> > > > + UL != UL_ALL is need to unroll small loop at O2. */
> > > > + class loop *loop_father = loop_outer (loop);
> > > > + if (loop->inner || !loop_father
> > >
> > > Do we ever get here for !loop_father? We shouldn't.
> > >
> > > > + || loop_father->latch == EXIT_BLOCK_PTR_FOR_FN (cfun)
> > >
> > > This means you excempt all loops that are direct children of the loop
> > > root tree. That doesn't make much sense.
> > >
> > > > + || ul != UL_ALL)
> > >
> > > This is also quite odd - we're being more optimistic for UL_NO_GROWTH
> > > than for UL_ALL? This doesn't make much sense.
> > >
> > > Overall I think this means removal of being optimistic doesn't work so
> > > well?
> > They're mostly used to avoid testcase regressions., the regressed
> > testcases rely on the behavior of complete unroll from the first
> > unroll, but now it's only unrolled by the second unroll.
> > I checked some, the codegen are the same, I need to go through all of
> > them, if the final codegen are the same or optimal, I'll just adjust
> > testcases?
> >
> > ++: g++.dg/warn/Warray-bounds-20.C -std=gnu++14 LP64 note (test for
> >
> > g++warnings, line 56)
> >
> > g++: g++.dg/warn/Warray-bounds-20.C -std=gnu++14 note (test for
> >
> > g++warnings, line 66)
> >
> > g++: g++.dg/warn/Warray-bounds-20.C -std=gnu++17 LP64 note (test for
> >
> > g++warnings, line 56)
> >
> > g++: g++.dg/warn/Warray-bounds-20.C -std=gnu++17 note (test for
> >
> > g++warnings, line 66)
> >
> > g++: g++.dg/warn/Warray-bounds-20.C -std=gnu++20 LP64 note (test for
> >
> > g++warnings, line 56)
> >
> > g++: g++.dg/warn/Warray-bounds-20.C -std=gnu++20 note (test for
> >
> > g++warnings, line 66)
> >
> > g++: g++.dg/warn/Warray-bounds-20.C -std=gnu++98 LP64 note (test for
> >
> > g++warnings, line 56)
> >
> > g++: g++.dg/warn/Warray-bounds-20.C -std=gnu++98 note (test for
> >
> > g++warnings, line 66)
>
> This seems to expect unrolling for an init loop rolling 1 times. I don't
> see 1/3 of the stmts vanishing but it's definitely an interesting corner
> case. That's why I was thinking of maybe adding a --param specifying
> an absolute growth we consider "no growth" - but of course that's
> ugly as well but it would cover these small loops.
>
> How do the sizes play out here after your change? Before it's
>
> size: 13-3, last_iteration: 2-2
> Loop size: 13
> Estimated size after unrolling: 13
>
> and the init is quite complex with virtual pointer inits. We do have
>
> size: 1 _14 = _5 + -1;
> Induction variable computation will be folded away.
> size: 1 _15 = _4 + 40;
> BB: 3, after_exit: 1
>
> where we don't realize the + 40 of _15 will be folded into the dereferences
> but that would only subtract 1.
>
> size: 3 C::C (_23, &MEM <const void *[8]> [(void *)&_ZTT2D1 + 48B]);
>
> that's the biggest cost.
>
> To diagnose the array bound issue we rely on early unrolling since we avoid
> -Warray-bounds after late unrolling due to false positives.
>
> This is definitely not an unrolling that preserves code size.
>
> > gcc: gcc.dg/Warray-bounds-68.c (test for warnings, line 18)
> >
> > gcc: gcc.dg/graphite/interchange-8.c execution test
>
> An execute fail is bad ... can we avoid this (but file a bugreport!) when
> placing #pragma GCC unroll before the innermost loop? We should
> probably honor that in early unrolling (not sure if we do).
>
> > gcc: gcc.dg/tree-prof/update-cunroll-2.c scan-tree-dump-not optimized
> > "Invalid sum"
> >
> > gcc: gcc.dg/tree-ssa/cunroll-1.c scan-tree-dump cunrolli "Last
> > iteration exit edge was proved true."
> >
> > gcc: gcc.dg/tree-ssa/cunroll-1.c scan-tree-dump cunrolli "loop with 2
> > iterations completely unrolled"
>
> again the current estimate is the same before/after unrolling, here
> we expect to retain one compare & branch.
>
> > gcc: gcc.dg/tree-ssa/dump-6.c scan-tree-dump store-merging "MEM
> > <unsigned long> \\[\\(char \\*\\)\\&a8] = "
> >
> > gcc: gcc.dg/tree-ssa/loop-36.c scan-tree-dump-not dce3 "c.array"
>
> again the 2/3 scaling is difficult to warrant. The goal of the early
> unrolling
> pass was abstraction penalty removal which works for low trip-count loops.
> So maybe that new --param for allowed growth should scale but instead
> of scaling by the loop size as 2/3 does it should scale by the number of
> times we peel which means offsetting the body size estimate by a constant.
>
> Honza? Any idea how to go forward here?
>
> Thanks,
> Richard.
>
> > gcc: gcc.dg/tree-ssa/ssa-dom-cse-5.c scan-tree-dump-times dom2 "return 3;" 1
> >
> > gcc: gcc.dg/tree-ssa/update-cunroll.c scan-tree-dump-times optimized
> > "Invalid sum" 0
> >
> > gcc: gcc.dg/tree-ssa/vrp88.c scan-tree-dump vrp1 "Folded into: if.*"
> >
> > gcc: gcc.dg/vect/no-vfa-vect-dv-2.c scan-tree-dump-times vect
> > "vectorized 3 loops" 1
> >
> > >
> > > If we need some extra leeway for UL_NO_GROWTH for what we expect
> > > to unroll it might be better to add sth like --param
> > > nogrowth-completely-peeled-insns
Hard to find a default value satisfying all testcases.
some require loop unroll with 7 insns increment, some don't want loop
unroll w/ 5 insn increment.
The original 2/3 reduction happened to meet all those testcases(or the
testcases are constructed based on the old 2/3).
Can we define the parameter as the size of the loop, below the size we
still do the reduction, so the small loop can be unrolled?
> > > specifying a fixed surplus size? Or we need to look at what's the problem
> > > with the testcases regressing or the one you are trying to fix.
> > >
> > > I did experiment with better estimating cleanup done at some point
> > > (see attached),
> > > but didn't get to finishing that (and as said, as we're running VN on the
> > > result
> > > we'd ideally do that as part of the estimation somehow).
> > >
> > > Richard.
> > >
> > > > + unr_insns = unr_insns * 2 / 3;
> > > > +
> > > > if (unr_insns <= 0)
> > > > unr_insns = 1;
> > > >
> > > > @@ -837,7 +847,7 @@ try_unroll_loop_completely (class loop *loop,
> > > >
> > > > unsigned HOST_WIDE_INT ninsns = size.overall;
> > > > unsigned HOST_WIDE_INT unr_insns
> > > > - = estimated_unrolled_size (&size, n_unroll);
> > > > + = estimated_unrolled_size (&size, n_unroll, ul, loop);
> > > > if (dump_file && (dump_flags & TDF_DETAILS))
> > > > {
> > > > fprintf (dump_file, " Loop size: %d\n", (int) ninsns);
> > > > --
> > > > 2.31.1
> > > >
> >
> >
> >
> > --
> > BR,
> > Hongtao
--
BR,
Hongtao
