Hi Richard,
Thanks for the review.
On Thu, 8 Nov 2018 at 00:03, Richard Biener <richard.guent...@gmail.com> wrote:
>
> On Fri, Nov 2, 2018 at 10:02 AM Kugan Vivekanandarajah
> <kugan.vivekanandara...@linaro.org> wrote:
> >
> > Hi Richard,
> > Thanks for the review.
> > On Tue, 30 Oct 2018 at 01:25, Richard Biener <richard.guent...@gmail.com>
> > wrote:
> > >
> > > On Mon, Oct 29, 2018 at 2:06 AM Kugan Vivekanandarajah
> > > <kugan.vivekanandara...@linaro.org> wrote:
> > > >
> > > > Hi Richard and Jeff,
> > > >
> > > > Thanks for your comments.
> > > >
> > > > On Fri, 26 Oct 2018 at 19:40, Richard Biener
> > > > <richard.guent...@gmail.com> wrote:
> > > > >
> > > > > On Fri, Oct 26, 2018 at 4:55 AM Jeff Law <l...@redhat.com> wrote:
> > > > > >
> > > > > > On 10/25/18 4:33 PM, Kugan Vivekanandarajah wrote:
> > > > > > > Hi,
> > > > > > >
> > > > > > > PR87528 showed a case where libgcc generated popcount is causing
> > > > > > > regression for Skylake.
> > > > > > > We also have PR86677 where kernel build is failing because the
> > > > > > > kernel
> > > > > > > does not use the libgcc (when backend is not defining popcount
> > > > > > > pattern). While I agree that the kernel should implement its own
> > > > > > > functionality when it is not using the libgcc, I am afraid that
> > > > > > > the
> > > > > > > implementation can have the same performance issues reported for
> > > > > > > Skylake in PR87528.
> > > > > > >
> > > > > > > Therefore, I would like to propose that we disable popcount
> > > > > > > detection
> > > > > > > when we don't have a pattern for that. The attached patch (based
> > > > > > > on
> > > > > > > previous discussions) does this.
> > > > > > >
> > > > > > > Bootstrapped and regression tested on x86_64-linux-gnu with no new
> > > > > > > regressions. We need to disable the popcount* testcases. I will
> > > > > > > have
> > > > > > > to define a effective_target_with_popcount in
> > > > > > > gcc/testsuite/lib/target-supports.exp if this patch is OK?
> > > > > > > Thanks,
> > > > > > > Kugan
> > > > > > >
> > > > > > >
> > > > > > > gcc/ChangeLog:
> > > > > > >
> > > > > > > 2018-10-25 Kugan Vivekanandarajah <kug...@linaro.org>
> > > > > > >
> > > > > > > * tree-scalar-evolution.c (expression_expensive_p): Make
> > > > > > > BUILTIN POPCOUNT
> > > > > > > as expensive when backend does not define it.
> > > > > > >
> > > > > > >
> > > > > > > gcc/testsuite/ChangeLog:
> > > > > > >
> > > > > > > 2018-10-25 Kugan Vivekanandarajah <kug...@linaro.org>
> > > > > > >
> > > > > > > * gcc.target/aarch64/popcount4.c: New test.
> > > > > > >
> > > > > > FWIW, I've been disabling by checking direct_optab_handler elsewhere
> > > > > > (number_of_iterations_popcount) in my tester. It may in fact be an
> > > > > > old
> > > > > > patch from you.
> > > > > >
> > > > > > Richi argued that it's the kernel team's responsibility to provide a
> > > > > > popcount since they don't link with libgcc. And I'm generally in
> > > > > > agreement with that position, though it does tend to generate some
> > > > > > friction with the kernel developers. We also run the real risk of
> > > > > > GCC 9
> > > > > > not being able to build the kernel which, IMHO, would be a disaster
> > > > > > from
> > > > > > a PR standpoint.
> > > > > >
> > > > > > I'd like to hear from others here. I fully realize we're beyond the
> > > > > > realm of what is strictly technically correct here from a review
> > > > > > standpoint.
> > > > >
> > > > > As said final value replacement to a library call is probably not
> > > > > wanted
> > > > > for optimization purpose, so adjusting expression_expensive_p is OK
> > > > > with
> > > > > me. It might not fully solve the (non-)issue in case another
> > > > > optimization pass
> > > > > chooses to materialize niter computation result.
> > > > >
> > > > > Few comments on the patch:
> > > > >
> > > > > + tree fndecl = get_callee_fndecl (expr);
> > > > > +
> > > > > + if (fndecl && DECL_BUILT_IN_CLASS (fndecl) == BUILT_IN_NORMAL)
> > > > > + {
> > > > > + combined_fn cfn = as_combined_fn (DECL_FUNCTION_CODE
> > > > > (fndecl));
> > > > >
> > > > > combined_fn cfn = gimple_call_combined_fn (expr);
> > > > > switch (cfn)
> > > > > {
> > > >
> > > > Did you mean:
> > > > combined_fn cfn = get_call_combined_fn (expr);
> > >
> > > Yes.
> > >
> > > > > ...
> > > > >
> > > > > cfn will be CFN_LAST for a non-builtin/internal call. I know Richard
> > > > > is mostly
> > > > > offline but eventually he knows whether there is a better way to query
> > > > >
> > > > > + CASE_CFN_POPCOUNT:
> > > > > + /* Check if opcode for popcount is available. */
> > > > > + if (optab_handler (popcount_optab,
> > > > > + TYPE_MODE (TREE_TYPE (CALL_EXPR_ARG
> > > > > (expr, 0))))
> > > > > + == CODE_FOR_nothing)
> > > > > + return true;
> > > > >
> > > > > note that we currently generate builtin calls rather than IFN calls
> > > > > (when a direct
> > > > > optab is supported).
> > > > >
> > > > > Another comment on the patch is that you probably have to adjust
> > > > > existing
> > > > > popcount testcases to add architecture specific flags enabling suport
> > > > > for
> > > > > the instructions, otherwise you won't see loop replacement.
> > > > Indeed.
> > > > In lib/target-supports.exp, I will try to add support for
> > > > check_effective_target_popcount_long.
> > > > When I grep for the popcount pattern in md files, I see it is defined
> > > > for:
> > > >
> > > > tilegx
> > > > tilepro
> > > > alpha
> > > > aarch64 when TARGET_SIMD
> > > > ia64
> > > > rs6000
> > > > i386 when TARGET_POPCOUNT
> > > > popwerpcspce when TARGET_POPCNTB || TARGET_POPCNTD
> > > > s390 when TARGET_Z916 && TARGET_64BIT
> > > > sparc when TARGET_POPC
> > > > arm when TARGET_NEON
> > > > mips when ISA_HAS_POP
> > > > spu
> > > > avr
> > > >
> > > > I can check these targets with the condition.
> > > > Another possibility is to check with a sample code and see if we are
> > > > getting a libcall in the asm. Not sure if that is straightforward. Are
> > > > there any example for such.
> > >
> > > You could try linking w/o libgcc ...
> > I realized that there are some examples already and I have based it
> > on that. Attached patch
> > 0001-fix-kernel-build-v3.patch does this. Bootstrapped and regression
> > tested on aarch64-linux-gnu with no new regression. Is this OK?
>
> I suspect using sth like the hard-float test is better, thus
>
> check_no_messages_and_pattern popcountl "!\\(call" rtl-expand
>
> instead of looking for !__popcount in assembly since depending on
> assembler syntax this might nor might not match spuriously...
Ok.
>
> @@ -3501,6 +3504,19 @@ expression_expensive_p (tree expr)
> tree arg;
> call_expr_arg_iterator iter;
>
> + combined_fn cfn = get_call_combined_fn (expr);
> + switch (cfn)
> + {
> + CASE_CFN_POPCOUNT:
> + /* Check if opcode for popcount is available. */
> + if (optab_handler (popcount_optab,
> + TYPE_MODE (TREE_TYPE (CALL_EXPR_ARG (expr, 0))))
> + == CODE_FOR_nothing)
> + return true;
> + default:
> + break;
> + }
> +
> if (!is_inexpensive_builtin (get_callee_fndecl (expr)))
> return true;
> FOR_EACH_CALL_EXPR_ARG (arg, iter, expr)
>
> note that we can handle double-word popcount by emitting two single-word
> popcount instructions. So if the mode is of 2 * UNITS_PER_WORD size
> you want to check for mode == word_mode. See expand_unop.
Ok
>
> I think you want to add a comment before the code explaining that even
> though is_inexpensive_builtin says true we may get a library call which
> we consider expensive.
Ok.
>
> > >
> > > > We could also move these test to a primary target that is tested often
> > > > tested which also defines popcount pattern. I dont think these tests
> > > > change for targets and if we can test in one target that could be
> > > > enough,
> > > >
> > > > I am happy to implement what is appropriate.
> > >
> > > How about the -Os idea?
> > Attached patch 0002-allow-builtin-popcount-for-size_p.patch attempts
> > this. As you mentioned, this will again break the kernel. While I am
> > trying to provide the popcount implementation for the newer kernel, it
> > will still be a problem for existing kernel versions. May I request
> > that we provide a flag to disable this if we decide to go with the
> > patch please?
>
> Let's consider this only for GCC 10 and get the first patch ready.
> expression_expensive_p shouldn't consider division as expensive
> for -Os either so there's more churn here and expression_expensive_p
> doesn't consider the overall size of the expression anyways.
>
> So let's drop this for now.
Ok.
I am attaching the modifies patch. Is this OK now?
Bootstrapped and regression tested on aarch64-linux-gnu with no new regressions.
Thanks,
Kugan
>
> Richard.
>
> > Thanks,
> > Kugan
> >
> > >
> > > Richard.
> > >
> > > > Thanks,
> > > > Kugan
> > > >
> > > >
> > > >
> > > > >
> > > > > Also I think that the expression is only expensive (for final value
> > > > > replacement!)
> > > > > if you consider optimizing for speed. When optimizing for size
> > > > > getting rid of
> > > > > the loop is probably beneificial unconditionally. That would leave
> > > > > the
> > > > > possibility to switch said testcases to -Os. It would require adding
> > > > > a
> > > > > bool size_p flag to expression_expensive and passing down
> > > > > optimize_loop_for_size_p ().
> > > > >
> > > > > _NOTE_ that expression_expensive_p is also used by IVOPTs and there
> > > > > replacing sth with an expression based on the niter analysis result
> > > > > doesn't
> > > > > mean we get rid of the loop (but only of an IV), so maybe that
> > > > > reasoning
> > > > > doesn't apply there.
> > > > >
> > > > > Richard.
> > > > >
> > > > > > Jeff
> > > > > >
From 8dbe11f716fe1d8cbe69e6879027ef6ed4db2334 Mon Sep 17 00:00:00 2001
From: Kugan Vivekanandarajah <kugan.vivekanandara...@linaro.org>
Date: Wed, 24 Oct 2018 20:33:50 +1100
Subject: [PATCH] fix kernel build [v3]
Change-Id: I0748f522fa83ffbc627b190e0b6cf3c4389338c5
---
gcc/testsuite/g++.dg/tree-ssa/pr86544.C | 1 +
gcc/testsuite/gcc.dg/tree-ssa/popcount.c | 1 +
gcc/testsuite/gcc.dg/tree-ssa/popcount2.c | 1 +
gcc/testsuite/gcc.dg/tree-ssa/popcount3.c | 1 +
gcc/testsuite/gcc.target/aarch64/popcount4.c | 14 ++++++++++++
gcc/testsuite/lib/target-supports.exp | 11 ++++++++++
gcc/tree-scalar-evolution.c | 33 ++++++++++++++++++++++++++++
7 files changed, 62 insertions(+)
create mode 100644 gcc/testsuite/gcc.target/aarch64/popcount4.c
diff --git a/gcc/testsuite/g++.dg/tree-ssa/pr86544.C b/gcc/testsuite/g++.dg/tree-ssa/pr86544.C
index fd844b4..ef43891 100644
--- a/gcc/testsuite/g++.dg/tree-ssa/pr86544.C
+++ b/gcc/testsuite/g++.dg/tree-ssa/pr86544.C
@@ -1,4 +1,5 @@
/* { dg-do compile } */
+/* { dg-require-effective-target popcountl } */
/* { dg-options "-O2 -fdump-tree-phiopt4 -fdump-tree-optimized" } */
int PopCount (long b) {
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/popcount.c b/gcc/testsuite/gcc.dg/tree-ssa/popcount.c
index a5ec3b3..b469410 100644
--- a/gcc/testsuite/gcc.dg/tree-ssa/popcount.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/popcount.c
@@ -1,4 +1,5 @@
/* { dg-do compile } */
+/* { dg-require-effective-target popcountl } */
/* { dg-options "-O3 -fdump-tree-optimized -fno-tree-ch" } */
extern int foo (int);
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/popcount2.c b/gcc/testsuite/gcc.dg/tree-ssa/popcount2.c
index 9096c6b..ef73e34 100644
--- a/gcc/testsuite/gcc.dg/tree-ssa/popcount2.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/popcount2.c
@@ -1,4 +1,5 @@
/* { dg-do run } */
+/* { dg-require-effective-target popcountl } */
/* { dg-options "-O2 -fno-tree-ch -fdump-tree-optimized" } */
int
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/popcount3.c b/gcc/testsuite/gcc.dg/tree-ssa/popcount3.c
index fd844b4..ef43891 100644
--- a/gcc/testsuite/gcc.dg/tree-ssa/popcount3.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/popcount3.c
@@ -1,4 +1,5 @@
/* { dg-do compile } */
+/* { dg-require-effective-target popcountl } */
/* { dg-options "-O2 -fdump-tree-phiopt4 -fdump-tree-optimized" } */
int PopCount (long b) {
diff --git a/gcc/testsuite/gcc.target/aarch64/popcount4.c b/gcc/testsuite/gcc.target/aarch64/popcount4.c
new file mode 100644
index 0000000..ee55b2e
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/popcount4.c
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized -mgeneral-regs-only" } */
+
+int PopCount (long b) {
+ int c = 0;
+
+ while (b) {
+ b &= b - 1;
+ c++;
+ }
+ return c;
+}
+
+/* { dg-final { scan-tree-dump-times "__builtin_popcount" 0 "optimized" } } */
diff --git a/gcc/testsuite/lib/target-supports.exp b/gcc/testsuite/lib/target-supports.exp
index e0c5801..8e16efc 100644
--- a/gcc/testsuite/lib/target-supports.exp
+++ b/gcc/testsuite/lib/target-supports.exp
@@ -6522,6 +6522,17 @@ proc check_effective_target_sync_long_long { } {
}
}
+# Return 1 if the target supports popcount on long.
+
+proc check_effective_target_popcountl { } {
+ return [check_no_messages_and_pattern popcountl "!\\(call" rtl-expand {
+ int foo (long b)
+ {
+ return __builtin_popcountl (b);
+ }
+ } "" ]
+}
+
# Return 1 if the target supports atomic operations on "long long"
# and can execute them.
#
diff --git a/gcc/tree-scalar-evolution.c b/gcc/tree-scalar-evolution.c
index 02174b1..964712c 100644
--- a/gcc/tree-scalar-evolution.c
+++ b/gcc/tree-scalar-evolution.c
@@ -257,7 +257,9 @@ along with GCC; see the file COPYING3. If not see
#include "system.h"
#include "coretypes.h"
#include "backend.h"
+#include "target.h"
#include "rtl.h"
+#include "optabs-query.h"
#include "tree.h"
#include "gimple.h"
#include "ssa.h"
@@ -282,6 +284,7 @@ along with GCC; see the file COPYING3. If not see
#include "gimple-fold.h"
#include "tree-into-ssa.h"
#include "builtins.h"
+#include "case-cfn-macros.h"
static tree analyze_scalar_evolution_1 (struct loop *, tree);
static tree analyze_scalar_evolution_for_address_of (struct loop *loop,
@@ -3500,6 +3503,36 @@ expression_expensive_p (tree expr)
{
tree arg;
call_expr_arg_iterator iter;
+ /* Even though is_inexpensive_builtin might say true, we will get a
+ library call for popcount when backend does not have an instruction
+ to do so. We consider this to be expenseive and generate
+ __builtin_popcount only when backend defines it. */
+ combined_fn cfn = get_call_combined_fn (expr);
+ switch (cfn)
+ {
+ CASE_CFN_POPCOUNT:
+ /* Check if opcode for popcount is available in the mode required. */
+ if (optab_handler (popcount_optab,
+ TYPE_MODE (TREE_TYPE (CALL_EXPR_ARG (expr, 0))))
+ == CODE_FOR_nothing)
+ {
+ machine_mode mode;
+ mode = TYPE_MODE (TREE_TYPE (CALL_EXPR_ARG (expr, 0)));
+ scalar_int_mode int_mode;
+
+ /* If the mode is of 2 * UNITS_PER_WORD size, we can handle
+ double-word popcount by emitting two single-word popcount
+ instructions. */
+ if (is_a <scalar_int_mode> (mode, &int_mode)
+ && GET_MODE_SIZE (int_mode) == 2 * UNITS_PER_WORD
+ && (optab_handler (popcount_optab, word_mode)
+ != CODE_FOR_nothing))
+ break;
+ return true;
+ }
+ default:
+ break;
+ }
if (!is_inexpensive_builtin (get_callee_fndecl (expr)))
return true;
--
2.7.4
