[V2] Use preferred mode for doloop iv [PR61837].

Major changes from v1:
* Add target hook to query preferred doloop mode.
* Recompute doloop iv base from niter under preferred mode.

Currently, doloop.xx variable is using the type as niter which may shorter
than word size.  For some cases, it would be better to use word size type.
For example, on 64bit system, to access 32bit value, subreg maybe used.
Then using 64bit type maybe better for niter if it can be present in
both 32bit and 64bit.

This patch add target hook for querg perferred mode for doloop iv.
And update doloop iv mode accordingly.

Bootstrap and regtest pass on powerpc64le, is this ok for trunk?

BR.
Jiufu

gcc/ChangeLog:

2021-07-13  Jiufu Guo  <guojiufu@linux.ibm.com>

	PR target/61837
	* config/rs6000/rs6000.c (TARGET_PREFERRED_DOLOOP_MODE): New hook.
	(rs6000_preferred_doloop_mode): New hook.
	* doc/tm.texi: Regenerated.
	* doc/tm.texi.in: Add hook preferred_doloop_mode.
	* target.def (preferred_doloop_mode): New hook.
	* targhooks.c (default_preferred_doloop_mode): New hook.
	* targhooks.h (default_preferred_doloop_mode): New hook.
	* tree-ssa-loop-ivopts.c (compute_doloop_base_on_mode): New function.
	(add_iv_candidate_for_doloop): Call targetm.preferred_doloop_mode
	and compute_doloop_base_on_mode.

gcc/testsuite/ChangeLog:

2021-07-13  Jiufu Guo  <guojiufu@linux.ibm.com>

	PR target/61837
	* gcc.target/powerpc/pr61837.c: New test.
---
 gcc/config/rs6000/rs6000.c                 |  9 +++
 gcc/doc/tm.texi                            |  4 ++
 gcc/doc/tm.texi.in                         |  2 +
 gcc/target.def                             |  7 +++
 gcc/targhooks.c                            |  8 +++
 gcc/targhooks.h                            |  2 +
 gcc/testsuite/gcc.target/powerpc/pr61837.c | 16 ++++++
 gcc/tree-ssa-loop-ivopts.c                 | 66 +++++++++++++++++++++-
 8 files changed, 112 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/gcc.target/powerpc/pr61837.c

Hi!

On Tue, Jul 13, 2021 at 08:50:46PM +0800, Jiufu Guo wrote:
> 	* doc/tm.texi: Regenerated.

Pet peeve: "Regenerate.", no "d".

> +DEFHOOK
> +(preferred_doloop_mode,
> + "This hook returns a more preferred mode or the @var{mode} itself.",
> + machine_mode,
> + (machine_mode mode),
> + default_preferred_doloop_mode)

You need a bit more description here.  What does the value it returns
mean?  If you want to say "a more preferred mode or the mode itself",
you should explain what the difference means, too.

You also should say the hook does not need to test if things will fit,
since the generic code already does.

And say this should return a MODE_INT always -- you never test for that
as far as I can see, but you don't need to, as long as everyone does the
sane thing.  So just state every hok implementation should :-)

> +extern machine_mode
> +default_preferred_doloop_mode (machine_mode);

One line please (this is a declaration).

> +/* { dg-do compile } */
> +/* { dg-options "-O2" } */
> +void foo(int *p1, long *p2, int s)
> +{
> +  int n, v, i;
> +
> +  v = 0;
> +  for (n = 0; n <= 100; n++) {
> +     for (i = 0; i < s; i++)
> +        if (p2[i] == n)
> +           p1[i] = v;
> +     v += 88;
> +  }
> +}
> +
> +/* { dg-final { scan-assembler-not {\mrldicl\M} } } */

That is a pretty fragile thing to test for.  It also need a line or two
of comment in the test case what this does, what kind of thing it does
not want to see.

> +/* If PREFERRED_MODE is suitable and profitable, use the preferred
> +   PREFERRED_MODE to compute doloop iv base from niter: base = niter + 1.  */
> +
> +static tree
> +compute_doloop_base_on_mode (machine_mode preferred_mode, tree niter,
> +			     const widest_int &iterations_max)
> +{
> +  tree ntype = TREE_TYPE (niter);
> +  tree pref_type = lang_hooks.types.type_for_mode (preferred_mode, 1);
> +
> +  gcc_assert (pref_type && TYPE_UNSIGNED (ntype));

Should that be pref_type instead of ntype?  If not, write it as two
separate asserts please.

> +static machine_mode
> +rs6000_preferred_doloop_mode (machine_mode)
> +{
> +  return word_mode;
> +}

This is fine if the generic code does the right thing if it passes say
TImode here, and if it never will pass some other mode class mode.


Segher

On 2021-07-14 04:50, Segher Boessenkool wrote:
> Hi!
> 
> On Tue, Jul 13, 2021 at 08:50:46PM +0800, Jiufu Guo wrote:
>> 	* doc/tm.texi: Regenerated.
> 
> Pet peeve: "Regenerate.", no "d".

Ok, yeap. While, 'Regenerate and Regenerated' were used by commits 
somewhere :)

> 
>> +DEFHOOK
>> +(preferred_doloop_mode,
>> + "This hook returns a more preferred mode or the @var{mode} itself.",
>> + machine_mode,
>> + (machine_mode mode),
>> + default_preferred_doloop_mode)
> 
> You need a bit more description here.  What does the value it returns
> mean?  If you want to say "a more preferred mode or the mode itself",
> you should explain what the difference means, too.

Ok, thanks.

> 
> You also should say the hook does not need to test if things will fit,
> since the generic code already does.
> 
> And say this should return a MODE_INT always -- you never test for that
> as far as I can see, but you don't need to, as long as everyone does 
> the
> sane thing.  So just state every hok implementation should :-)

Yes, the preferred 'doloop iv mode' from targets should be a MODE_INT.
I will add comments, and update the gcc_assert you mentioned below
for this.

Thanks a lot for your comments and suggestions!

When writing words, I was always from adding/deleting and still hard to 
get
perfect ones -:(

> 
>> +extern machine_mode
>> +default_preferred_doloop_mode (machine_mode);
> 
> One line please (this is a declaration).
> 
>> +/* { dg-do compile } */
>> +/* { dg-options "-O2" } */
>> +void foo(int *p1, long *p2, int s)
>> +{
>> +  int n, v, i;
>> +
>> +  v = 0;
>> +  for (n = 0; n <= 100; n++) {
>> +     for (i = 0; i < s; i++)
>> +        if (p2[i] == n)
>> +           p1[i] = v;
>> +     v += 88;
>> +  }
>> +}
>> +
>> +/* { dg-final { scan-assembler-not {\mrldicl\M} } } */
> 
> That is a pretty fragile thing to test for.  It also need a line or two
> of comment in the test case what this does, what kind of thing it does
> not want to see.

Thanks! I will update accordingly.  And I'm thinking to add tests to 
check
doloop.xx type: no zero_extend to access subreg. This is the intention
of this patch.

> 
>> +/* If PREFERRED_MODE is suitable and profitable, use the preferred
>> +   PREFERRED_MODE to compute doloop iv base from niter: base = niter 
>> + 1.  */
>> +
>> +static tree
>> +compute_doloop_base_on_mode (machine_mode preferred_mode, tree niter,
>> +			     const widest_int &iterations_max)
>> +{
>> +  tree ntype = TREE_TYPE (niter);
>> +  tree pref_type = lang_hooks.types.type_for_mode (preferred_mode, 
>> 1);
>> +
>> +  gcc_assert (pref_type && TYPE_UNSIGNED (ntype));
> 
> Should that be pref_type instead of ntype?  If not, write it as two
> separate asserts please.

Ok, will separate as two asserts.

> 
>> +static machine_mode
>> +rs6000_preferred_doloop_mode (machine_mode)
>> +{
>> +  return word_mode;
>> +}
> 
> This is fine if the generic code does the right thing if it passes say
> TImode here, and if it never will pass some other mode class mode.

The generic code checks if the returned mode can works on doloop iv 
correctly,
if the preferred mode is not suitable (e.g. preferred_doloop_mode 
returns DI,
but niter is a large value in TI), then doloop.xx IV will use the 
original mode.

When a target really prefer TImode, and TImode can represent number of 
iterations,
This would still work.  In current code, word_mode is SI/DI in most 
targets, like Pmode.
On powerpc, they are DImode (for 64bit)/SImode(32bit)

Thanks again for your comments!

BR,
Jiufu

> 
> 
> Segher

On 2021-07-14 12:40, guojiufu via Gcc-patches wrote:
Updated the patch as below:
Thanks for comments.

gcc/ChangeLog:

2021-07-13  Jiufu Guo  <guojiufu@linux.ibm.com>

	PR target/61837
	* config/rs6000/rs6000.c (TARGET_PREFERRED_DOLOOP_MODE): New hook.
	(rs6000_preferred_doloop_mode): New hook.
	* doc/tm.texi: Regenerate.
	* doc/tm.texi.in: Add hook preferred_doloop_mode.
	* target.def (preferred_doloop_mode): New hook.
	* targhooks.c (default_preferred_doloop_mode): New hook.
	* targhooks.h (default_preferred_doloop_mode): New hook.
	* tree-ssa-loop-ivopts.c (compute_doloop_base_on_mode): New function.
	(add_iv_candidate_for_doloop): Call targetm.preferred_doloop_mode
	and compute_doloop_base_on_mode.

gcc/testsuite/ChangeLog:

2021-07-13  Jiufu Guo  <guojiufu@linux.ibm.com>

	PR target/61837
	* gcc.target/powerpc/pr61837.c: New test.
---
  gcc/config/rs6000/rs6000.c                 | 11 ++++
  gcc/doc/tm.texi                            | 10 ++++
  gcc/doc/tm.texi.in                         |  2 +
  gcc/target.def                             | 14 +++++
  gcc/targhooks.c                            |  8 +++
  gcc/targhooks.h                            |  1 +
  gcc/testsuite/gcc.target/powerpc/pr61837.c | 20 +++++++
  gcc/tree-ssa-loop-ivopts.c                 | 67 +++++++++++++++++++++-
  8 files changed, 131 insertions(+), 2 deletions(-)
  create mode 100644 gcc/testsuite/gcc.target/powerpc/pr61837.c

diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c
index 9a5db63d0ef..3bdf0cb97a3 100644
--- a/gcc/config/rs6000/rs6000.c
+++ b/gcc/config/rs6000/rs6000.c
@@ -1700,6 +1700,9 @@ static const struct attribute_spec 
rs6000_attribute_table[] =
  #undef TARGET_DOLOOP_COST_FOR_ADDRESS
  #define TARGET_DOLOOP_COST_FOR_ADDRESS 1000000000

+#undef TARGET_PREFERRED_DOLOOP_MODE
+#define TARGET_PREFERRED_DOLOOP_MODE rs6000_preferred_doloop_mode
+
  #undef TARGET_ATOMIC_ASSIGN_EXPAND_FENV
  #define TARGET_ATOMIC_ASSIGN_EXPAND_FENV 
rs6000_atomic_assign_expand_fenv

@@ -27867,6 +27870,14 @@ rs6000_predict_doloop_p (struct loop *loop)
    return true;
  }

+/* Implement TARGET_PREFERRED_DOLOOP_MODE. */
+
+static machine_mode
+rs6000_preferred_doloop_mode (machine_mode)
+{
+  return word_mode;
+}
+
  /* Implement TARGET_CANNOT_SUBSTITUTE_MEM_EQUIV_P.  */

  static bool
diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index 2a41ae5fba1..4fb516169dc 100644
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -11984,6 +11984,16 @@ By default, the RTL loop optimizer does not use 
a present doloop pattern for
  loops containing function calls or branch on table instructions.
  @end deftypefn

+@deftypefn {Target Hook} machine_mode TARGET_PREFERRED_DOLOOP_MODE 
(machine_mode @var{mode})
+This hook takes a @var{mode} which is the original mode of doloop IV.
+And if the target prefers other mode for doloop IV, this hook returns 
the
+preferred mode.
+For example, on 64bit target, DImode may be preferred than SImode.
+This hook could return the original mode itself if the target prefer to
+keep the original mode.
+The origianl mode and return mode should be MODE_INT.
+@end deftypefn
+
  @deftypefn {Target Hook} bool TARGET_LEGITIMATE_COMBINED_INSN (rtx_insn 
*@var{insn})
  Take an instruction in @var{insn} and return @code{false} if the 
instruction
  is not appropriate as a combination of two or more instructions.  The
diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in
index f881cdabe9e..38215149a92 100644
--- a/gcc/doc/tm.texi.in
+++ b/gcc/doc/tm.texi.in
@@ -7917,6 +7917,8 @@ to by @var{ce_info}.

  @hook TARGET_INVALID_WITHIN_DOLOOP

+@hook TARGET_PREFERRED_DOLOOP_MODE
+
  @hook TARGET_LEGITIMATE_COMBINED_INSN

  @hook TARGET_CAN_FOLLOW_JUMP
diff --git a/gcc/target.def b/gcc/target.def
index c009671c583..1b6c9872807 100644
--- a/gcc/target.def
+++ b/gcc/target.def
@@ -4454,6 +4454,20 @@ loops containing function calls or branch on 
table instructions.",
   const char *, (const rtx_insn *insn),
   default_invalid_within_doloop)

+/* Returns the machine mode which the target prefers for doloop IV.  */
+DEFHOOK
+(preferred_doloop_mode,
+ "This hook takes a @var{mode} which is the original mode of doloop 
IV.\n\
+And if the target prefers another mode for doloop IV, this hook returns 
the\n\
+preferred mode.\n\
+For example, on 64bit target, DImode may be preferred than SImode.\n\
+This hook could return the original mode itself if the target prefer 
to\n\
+keep the original mode.\n\
+The original mode and return mode should be MODE_INT.",
+ machine_mode,
+ (machine_mode mode),
+ default_preferred_doloop_mode)
+
  /* Returns true for a legitimate combined insn.  */
  DEFHOOK
  (legitimate_combined_insn,
diff --git a/gcc/targhooks.c b/gcc/targhooks.c
index 44a1facedcf..eb5190910dc 100644
--- a/gcc/targhooks.c
+++ b/gcc/targhooks.c
@@ -660,6 +660,14 @@ default_predict_doloop_p (class loop *loop 
ATTRIBUTE_UNUSED)
    return false;
  }

+/* By default, just use the input MODE itself.  */
+
+machine_mode
+default_preferred_doloop_mode (machine_mode mode)
+{
+  return mode;
+}
+
  /* NULL if INSN insn is valid within a low-overhead loop, otherwise 
returns
     an error message.

diff --git a/gcc/targhooks.h b/gcc/targhooks.h
index f70a307d26c..f92e102c450 100644
--- a/gcc/targhooks.h
+++ b/gcc/targhooks.h
@@ -88,6 +88,7 @@ extern bool default_fixed_point_supported_p (void);
  extern bool default_has_ifunc_p (void);

  extern bool default_predict_doloop_p (class loop *);
+extern machine_mode default_preferred_doloop_mode (machine_mode);
  extern const char * default_invalid_within_doloop (const rtx_insn *);

  extern tree default_builtin_vectorized_function (unsigned int, tree, 
tree);
diff --git a/gcc/testsuite/gcc.target/powerpc/pr61837.c 
b/gcc/testsuite/gcc.target/powerpc/pr61837.c
new file mode 100644
index 00000000000..87b69888c7e
--- /dev/null
+++ b/gcc/testsuite/gcc.target/powerpc/pr61837.c
@@ -0,0 +1,20 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-rtl-loop2_doloop -fno-unroll-loops" } */
+/* The inner loop would use the doloop IV in word_mode.  And then
+   there is no need to access it though zero_extend on shorter mode.  
*/
+void foo(int *p1, long *p2, int s)
+{
+  int n, v, i;
+
+  v = 0;
+  for (n = 0; n <= 100; n++) {
+     for (i = 0; i < s; i++)
+        if (p2[i] == n)
+           p1[i] = v;
+     v += 88;
+  }
+}
+
+/* { dg-final {scan-rtl-dump-not "zero_extend.*doloop" "loop2_doloop"} 
} */
+/* { dg-final {scan-rtl-dump-not "reg:SI.*doloop" "loop2_doloop" { 
target lp64 } } } */
+
diff --git a/gcc/tree-ssa-loop-ivopts.c b/gcc/tree-ssa-loop-ivopts.c
index 12a8a49a307..33da3184d6f 100644
--- a/gcc/tree-ssa-loop-ivopts.c
+++ b/gcc/tree-ssa-loop-ivopts.c
@@ -5657,6 +5657,57 @@ relate_compare_use_with_all_cands (struct 
ivopts_data *data)
      }
  }

+/* If PREFERRED_MODE is suitable and profitable, use the
+   PREFERRED_MODE to compute doloop iv base from niter: base = niter + 
1.  */
+
+static tree
+compute_doloop_base_on_mode (machine_mode preferred_mode, tree niter,
+			     const widest_int &iterations_max)
+{
+  tree ntype = TREE_TYPE (niter);
+  gcc_assert (TYPE_UNSIGNED (ntype));
+
+  tree pref_type = lang_hooks.types.type_for_mode (preferred_mode, 1);
+  gcc_assert (pref_type && TREE_CODE (pref_type) == INTEGER_TYPE);
+
+  int prec = TYPE_PRECISION (ntype);
+  int pref_prec = TYPE_PRECISION (pref_type);
+
+  tree base;
+
+  /* Check if the PREFERRED_MODED is able to present niter.  */
+  if (pref_prec > prec
+      || wi::ltu_p (iterations_max,
+		    widest_int::from (wi::max_value (pref_prec, UNSIGNED),
+				      UNSIGNED)))
+    {
+      /* No wrap, it is safe to use preferred type after niter + 1.  */
+      if (wi::ltu_p (iterations_max,
+		     widest_int::from (wi::max_value (prec, UNSIGNED),
+				       UNSIGNED)))
+	{
+	  /* This could help to optimize "-1 +1" pair when niter looks
+	     like "n-1": n is in original mode.  "base = (n - 1) + 1"
+	     in PREFERRED_MODED: it could be base = (PREFERRED_TYPE)n.  */
+	  base = fold_build2 (PLUS_EXPR, ntype, unshare_expr (niter),
+			      build_int_cst (ntype, 1));
+	  base = fold_convert (pref_type, base);
+	}
+
+      /* To avoid wrap, need fold niter to preferred type before plus 
1.  */
+      else
+	{
+	  niter = fold_convert (pref_type, niter);
+	  base = fold_build2 (PLUS_EXPR, pref_type, unshare_expr (niter),
+			      build_int_cst (pref_type, 1));
+	}
+    }
+  else
+    base = fold_build2 (PLUS_EXPR, ntype, unshare_expr (niter),
+			build_int_cst (ntype, 1));
+  return base;
+}
+
  /* Add one doloop dedicated IV candidate:
       - Base is (may_be_zero ? 1 : (niter + 1)).
       - Step is -1.  */
@@ -5688,8 +5739,20 @@ add_iv_candidate_for_doloop (struct ivopts_data 
*data)
  	return;
      }

-  tree base = fold_build2 (PLUS_EXPR, ntype, unshare_expr (niter),
-			   build_int_cst (ntype, 1));
+  machine_mode mode = TYPE_MODE (ntype);
+  machine_mode pref_mode = targetm.preferred_doloop_mode (mode);
+
+  tree base;
+  if (mode != pref_mode)
+    {
+      base = compute_doloop_base_on_mode (pref_mode, niter, 
niter_desc->max);
+      ntype = TREE_TYPE (base);
+    }
+  else
+    base = fold_build2 (PLUS_EXPR, ntype, unshare_expr (niter),
+			build_int_cst (ntype, 1));
+
+
    add_candidate (data, base, build_int_cst (ntype, -1), true, NULL, 
NULL, true);
  }

Hi!

On Wed, Jul 14, 2021 at 06:26:28PM +0800, guojiufu wrote:
> 	PR target/61837

Wrong PR number?

> +@deftypefn {Target Hook} machine_mode TARGET_PREFERRED_DOLOOP_MODE 
> (machine_mode @var{mode})
> +This hook takes a @var{mode} which is the original mode of doloop IV.
> +And if the target prefers other mode for doloop IV, this hook returns 
> the
> +preferred mode.
> +For example, on 64bit target, DImode may be preferred than SImode.
> +This hook could return the original mode itself if the target prefer to
> +keep the original mode.
> +The origianl mode and return mode should be MODE_INT.
> +@end deftypefn

(Typo, "original").  That has all the right contents, but needs someone
who is better at English than me to look at it / improve it.

> +/* { dg-final {scan-rtl-dump-not "zero_extend.*doloop" "loop2_doloop"} 
> } */
> +/* { dg-final {scan-rtl-dump-not "reg:SI.*doloop" "loop2_doloop" { 
> target lp64 } } } */

(Don't use format=flowed in your mails, or certainly not in those
containing patches -- it was rewrapped).

If you use .* in scan REs, you should be aware that "." matches newlines
by default, so you can match "reg:SI" on one line and "doloop" on a
later one, in that second one.

You can write

/* { dg-final {scan-rtl-dump-not {(?p)reg:SI.*doloop} "loop2_doloop" { target lp64 } } } */

(note: {} are much more convenient around most REs, you need a lot of
escaping without it) to get "partial newline-sensitive matching", which
is usually what you want (see "man re_syntax" for the details).


The generic changes look fine to me (but what do I know about Gimple!)
The rs6000 changes are fine if the rest is approved (and see the
testcase comments).  Thanks!


Segher

On 2021-07-15 02:04, Segher Boessenkool wrote:
> Hi!
> 
> On Wed, Jul 14, 2021 at 06:26:28PM +0800, guojiufu wrote:
>> 	PR target/61837
> 
> Wrong PR number?

There is a patch optimize "add -1; zero_ext; add +1" to "zero_ext" 
already.
Having this patch would help to avoid the left 'zero_ext', so, I reuse 
this
PR number.

> 
>> +@deftypefn {Target Hook} machine_mode TARGET_PREFERRED_DOLOOP_MODE
>> (machine_mode @var{mode})
>> +This hook takes a @var{mode} which is the original mode of doloop IV.
>> +And if the target prefers other mode for doloop IV, this hook returns
>> the
>> +preferred mode.
>> +For example, on 64bit target, DImode may be preferred than SImode.
>> +This hook could return the original mode itself if the target prefer 
>> to
>> +keep the original mode.
>> +The origianl mode and return mode should be MODE_INT.
>> +@end deftypefn
> 
> (Typo, "original").  That has all the right contents, but needs someone
> who is better at English than me to look at it / improve it.
> 
>> +/* { dg-final {scan-rtl-dump-not "zero_extend.*doloop" 
>> "loop2_doloop"}
>> } */
>> +/* { dg-final {scan-rtl-dump-not "reg:SI.*doloop" "loop2_doloop" {
>> target lp64 } } } */
> 
> (Don't use format=flowed in your mails, or certainly not in those
> containing patches -- it was rewrapped).
> 

Oh, thanks for point out this!

> If you use .* in scan REs, you should be aware that "." matches 
> newlines
> by default, so you can match "reg:SI" on one line and "doloop" on a
> later one, in that second one.
> 
> You can write
> 
> /* { dg-final {scan-rtl-dump-not {(?p)reg:SI.*doloop} "loop2_doloop" {
> target lp64 } } } */
> 
> (note: {} are much more convenient around most REs, you need a lot of
> escaping without it) to get "partial newline-sensitive matching", which
> is usually what you want (see "man re_syntax" for the details).

Thanks so much!  This helps me a lot about writing test cases, 
especially
on how to scan-xxx re in test case!

> 
> 
> The generic changes look fine to me (but what do I know about Gimple!)
> The rs6000 changes are fine if the rest is approved (and see the
> testcase comments).  Thanks!

Thanks again!

BR,
Jiufu

> 
> 
> Segher

On Tue, 13 Jul 2021, Jiufu Guo wrote:

> Major changes from v1:
> * Add target hook to query preferred doloop mode.
> * Recompute doloop iv base from niter under preferred mode.
> 
> Currently, doloop.xx variable is using the type as niter which may shorter
> than word size.  For some cases, it would be better to use word size type.
> For example, on 64bit system, to access 32bit value, subreg maybe used.
> Then using 64bit type maybe better for niter if it can be present in
> both 32bit and 64bit.
> 
> This patch add target hook for querg perferred mode for doloop iv.
> And update doloop iv mode accordingly.
> 
> Bootstrap and regtest pass on powerpc64le, is this ok for trunk?
> 
> BR.
> Jiufu
> 
> gcc/ChangeLog:
> 
> 2021-07-13  Jiufu Guo  <guojiufu@linux.ibm.com>
> 
> 	PR target/61837
> 	* config/rs6000/rs6000.c (TARGET_PREFERRED_DOLOOP_MODE): New hook.
> 	(rs6000_preferred_doloop_mode): New hook.
> 	* doc/tm.texi: Regenerated.
> 	* doc/tm.texi.in: Add hook preferred_doloop_mode.
> 	* target.def (preferred_doloop_mode): New hook.
> 	* targhooks.c (default_preferred_doloop_mode): New hook.
> 	* targhooks.h (default_preferred_doloop_mode): New hook.
> 	* tree-ssa-loop-ivopts.c (compute_doloop_base_on_mode): New function.
> 	(add_iv_candidate_for_doloop): Call targetm.preferred_doloop_mode
> 	and compute_doloop_base_on_mode.
> 
> gcc/testsuite/ChangeLog:
> 
> 2021-07-13  Jiufu Guo  <guojiufu@linux.ibm.com>
> 
> 	PR target/61837
> 	* gcc.target/powerpc/pr61837.c: New test.
> ---
>  gcc/config/rs6000/rs6000.c                 |  9 +++
>  gcc/doc/tm.texi                            |  4 ++
>  gcc/doc/tm.texi.in                         |  2 +
>  gcc/target.def                             |  7 +++
>  gcc/targhooks.c                            |  8 +++
>  gcc/targhooks.h                            |  2 +
>  gcc/testsuite/gcc.target/powerpc/pr61837.c | 16 ++++++
>  gcc/tree-ssa-loop-ivopts.c                 | 66 +++++++++++++++++++++-
>  8 files changed, 112 insertions(+), 2 deletions(-)
>  create mode 100644 gcc/testsuite/gcc.target/powerpc/pr61837.c
> 
> diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c
> index 9a5db63d0ef..444f3c49288 100644
> --- a/gcc/config/rs6000/rs6000.c
> +++ b/gcc/config/rs6000/rs6000.c
> @@ -1700,6 +1700,9 @@ static const struct attribute_spec rs6000_attribute_table[] =
>  #undef TARGET_DOLOOP_COST_FOR_ADDRESS
>  #define TARGET_DOLOOP_COST_FOR_ADDRESS 1000000000
>  
> +#undef TARGET_PREFERRED_DOLOOP_MODE
> +#define TARGET_PREFERRED_DOLOOP_MODE rs6000_preferred_doloop_mode
> +
>  #undef TARGET_ATOMIC_ASSIGN_EXPAND_FENV
>  #define TARGET_ATOMIC_ASSIGN_EXPAND_FENV rs6000_atomic_assign_expand_fenv
>  
> @@ -27867,6 +27870,12 @@ rs6000_predict_doloop_p (struct loop *loop)
>    return true;
>  }
>  
> +static machine_mode
> +rs6000_preferred_doloop_mode (machine_mode)
> +{
> +  return word_mode;
> +}
> +
>  /* Implement TARGET_CANNOT_SUBSTITUTE_MEM_EQUIV_P.  */
>  
>  static bool
> diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
> index 2a41ae5fba1..3f5881220f8 100644
> --- a/gcc/doc/tm.texi
> +++ b/gcc/doc/tm.texi
> @@ -11984,6 +11984,10 @@ By default, the RTL loop optimizer does not use a present doloop pattern for
>  loops containing function calls or branch on table instructions.
>  @end deftypefn
>  
> +@deftypefn {Target Hook} machine_mode TARGET_PREFERRED_DOLOOP_MODE (machine_mode @var{mode})
> +This hook returns a more preferred mode or the @var{mode} itself.
> +@end deftypefn
> +
>  @deftypefn {Target Hook} bool TARGET_LEGITIMATE_COMBINED_INSN (rtx_insn *@var{insn})
>  Take an instruction in @var{insn} and return @code{false} if the instruction
>  is not appropriate as a combination of two or more instructions.  The
> diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in
> index f881cdabe9e..38215149a92 100644
> --- a/gcc/doc/tm.texi.in
> +++ b/gcc/doc/tm.texi.in
> @@ -7917,6 +7917,8 @@ to by @var{ce_info}.
>  
>  @hook TARGET_INVALID_WITHIN_DOLOOP
>  
> +@hook TARGET_PREFERRED_DOLOOP_MODE
> +
>  @hook TARGET_LEGITIMATE_COMBINED_INSN
>  
>  @hook TARGET_CAN_FOLLOW_JUMP
> diff --git a/gcc/target.def b/gcc/target.def
> index c009671c583..91a96150e50 100644
> --- a/gcc/target.def
> +++ b/gcc/target.def
> @@ -4454,6 +4454,13 @@ loops containing function calls or branch on table instructions.",
>   const char *, (const rtx_insn *insn),
>   default_invalid_within_doloop)
>  
> +DEFHOOK
> +(preferred_doloop_mode,
> + "This hook returns a more preferred mode or the @var{mode} itself.",
> + machine_mode,
> + (machine_mode mode),
> + default_preferred_doloop_mode)
> +
>  /* Returns true for a legitimate combined insn.  */
>  DEFHOOK
>  (legitimate_combined_insn,
> diff --git a/gcc/targhooks.c b/gcc/targhooks.c
> index 44a1facedcf..eb5190910dc 100644
> --- a/gcc/targhooks.c
> +++ b/gcc/targhooks.c
> @@ -660,6 +660,14 @@ default_predict_doloop_p (class loop *loop ATTRIBUTE_UNUSED)
>    return false;
>  }
>  
> +/* By default, just use the input MODE itself.  */
> +
> +machine_mode
> +default_preferred_doloop_mode (machine_mode mode)
> +{
> +  return mode;
> +}
> +
>  /* NULL if INSN insn is valid within a low-overhead loop, otherwise returns
>     an error message.
>  
> diff --git a/gcc/targhooks.h b/gcc/targhooks.h
> index f70a307d26c..f0560b6ae34 100644
> --- a/gcc/targhooks.h
> +++ b/gcc/targhooks.h
> @@ -88,6 +88,8 @@ extern bool default_fixed_point_supported_p (void);
>  extern bool default_has_ifunc_p (void);
>  
>  extern bool default_predict_doloop_p (class loop *);
> +extern machine_mode
> +default_preferred_doloop_mode (machine_mode);
>  extern const char * default_invalid_within_doloop (const rtx_insn *);
>  
>  extern tree default_builtin_vectorized_function (unsigned int, tree, tree);
> diff --git a/gcc/testsuite/gcc.target/powerpc/pr61837.c b/gcc/testsuite/gcc.target/powerpc/pr61837.c
> new file mode 100644
> index 00000000000..dc44eb9cb41
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/powerpc/pr61837.c
> @@ -0,0 +1,16 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2" } */
> +void foo(int *p1, long *p2, int s)
> +{
> +  int n, v, i;
> +
> +  v = 0;
> +  for (n = 0; n <= 100; n++) {
> +     for (i = 0; i < s; i++)
> +        if (p2[i] == n)
> +           p1[i] = v;
> +     v += 88;
> +  }
> +}
> +
> +/* { dg-final { scan-assembler-not {\mrldicl\M} } } */
> diff --git a/gcc/tree-ssa-loop-ivopts.c b/gcc/tree-ssa-loop-ivopts.c
> index 12a8a49a307..92767a09b6c 100644
> --- a/gcc/tree-ssa-loop-ivopts.c
> +++ b/gcc/tree-ssa-loop-ivopts.c
> @@ -5657,6 +5657,56 @@ relate_compare_use_with_all_cands (struct ivopts_data *data)
>      }
>  }
>  
> +/* If PREFERRED_MODE is suitable and profitable, use the preferred
> +   PREFERRED_MODE to compute doloop iv base from niter: base = niter + 1.  */
> +
> +static tree
> +compute_doloop_base_on_mode (machine_mode preferred_mode, tree niter,
> +			     const widest_int &iterations_max)
> +{
> +  tree ntype = TREE_TYPE (niter);
> +  tree pref_type = lang_hooks.types.type_for_mode (preferred_mode, 1);

It's unlikely but type_for_mode can return NULL, so you shouldn't
assert but fall back to using the original type.  The assert for
TYPE_UNSIGNED is superfluous - you asked for an unsigned type already.

Otherwise the IVOPTs changes and the new target hook look OK, please
address Seghers comments though.

Thanks,
Richard.

> +  gcc_assert (pref_type && TYPE_UNSIGNED (ntype));
> +
> +  int prec = TYPE_PRECISION (ntype);
> +  int pref_prec = TYPE_PRECISION (pref_type);
> +
> +  tree base;
> +
> +  /* Check if the PREFERRED_MODED is able to present niter.  */
> +  if (pref_prec > prec
> +      || wi::ltu_p (iterations_max,
> +		    widest_int::from (wi::max_value (pref_prec, UNSIGNED),
> +				      UNSIGNED)))
> +    {
> +      /* No wrap, it is safe to use preferred type after niter + 1.  */
> +      if (wi::ltu_p (iterations_max,
> +		     widest_int::from (wi::max_value (prec, UNSIGNED),
> +				       UNSIGNED)))
> +	{
> +	  /* This could help to optimize "-1 +1" pair when niter looks
> +	     like "n-1": n is in original mode.  "base = (n - 1) + 1"
> +	     in PREFERRED_MODED: it could be base = (PREFERRED_TYPE)n.  */
> +	  base = fold_build2 (PLUS_EXPR, ntype, unshare_expr (niter),
> +			      build_int_cst (ntype, 1));
> +	  base = fold_convert (pref_type, base);
> +	}
> +
> +      /* To avoid wrap, need fold niter to preferred type before plus 1.  */
> +      else
> +	{
> +	  niter = fold_convert (pref_type, niter);
> +	  base = fold_build2 (PLUS_EXPR, pref_type, unshare_expr (niter),
> +			      build_int_cst (pref_type, 1));
> +	}
> +    }
> +  else
> +    base = fold_build2 (PLUS_EXPR, ntype, unshare_expr (niter),
> +			build_int_cst (ntype, 1));
> +  return base;
> +}
> +
>  /* Add one doloop dedicated IV candidate:
>       - Base is (may_be_zero ? 1 : (niter + 1)).
>       - Step is -1.  */
> @@ -5688,8 +5738,20 @@ add_iv_candidate_for_doloop (struct ivopts_data *data)
>  	return;
>      }
>  
> -  tree base = fold_build2 (PLUS_EXPR, ntype, unshare_expr (niter),
> -			   build_int_cst (ntype, 1));
> +  machine_mode mode = TYPE_MODE (ntype);
> +  machine_mode pref_mode = targetm.preferred_doloop_mode (mode);
> +
> +  tree base;
> +  if (mode != pref_mode)
> +    {
> +      base = compute_doloop_base_on_mode (pref_mode, niter, niter_desc->max);
> +      ntype = TREE_TYPE (base);
> +    }
> +  else
> +    base = fold_build2 (PLUS_EXPR, ntype, unshare_expr (niter),
> +			build_int_cst (ntype, 1));
> +
> +
>    add_candidate (data, base, build_int_cst (ntype, -1), true, NULL, NULL, true);
>  }
>  
>

> On 15 Jul 2021, at 06:09, guojiufu via Gcc-patches <gcc-patches@gcc.gnu.org> wrote:
> 
> On 2021-07-15 02:04, Segher Boessenkool wrote:
> 

>>> +@deftypefn {Target Hook} machine_mode TARGET_PREFERRED_DOLOOP_MODE
>>> (machine_mode @var{mode})
>>> +This hook takes a @var{mode} which is the original mode of doloop IV.
>>> +And if the target prefers other mode for doloop IV, this hook returns
>>> the
>>> +preferred mode.
>>> +For example, on 64bit target, DImode may be preferred than SImode.
>>> +This hook could return the original mode itself if the target prefer to
>>> +keep the original mode.
>>> +The origianl mode and return mode should be MODE_INT.
>>> +@end deftypefn
>> (Typo, "original").  That has all the right contents, but needs someone
>> who is better at English than me to look at it / improve it.

well.. how about this small tweak?

This hook takes a @var{mode} for a doloop IV, where @code{mode} is the original mode for the operation.  If the target prefers an alternate @code{mode} for the operation, then this hook should return that mode.  For example, on a 64-bit target, @code{DImode} might be preferred over @code{SImode}.  The original @code{mode} should be returned if that is suitable.  Both the original and the returned modes should be @code{MODE_INT}.

0.02GBP only.
Iain

Iain Sandoe <idsandoe@googlemail.com> writes:

>> On 15 Jul 2021, at 06:09, guojiufu via Gcc-patches 
>> <gcc-patches@gcc.gnu.org> wrote:
>> 
>> On 2021-07-15 02:04, Segher Boessenkool wrote:
>> 
>
>>>> +@deftypefn {Target Hook} machine_mode 
>>>> TARGET_PREFERRED_DOLOOP_MODE
>>>> (machine_mode @var{mode})
>>>> +This hook takes a @var{mode} which is the original mode of 
>>>> doloop IV.
>>>> +And if the target prefers other mode for doloop IV, this 
>>>> hook returns
>>>> the
>>>> +preferred mode.
>>>> +For example, on 64bit target, DImode may be preferred than 
>>>> SImode.
>>>> +This hook could return the original mode itself if the 
>>>> target prefer to
>>>> +keep the original mode.
>>>> +The origianl mode and return mode should be MODE_INT.
>>>> +@end deftypefn
>>> (Typo, "original").  That has all the right contents, but 
>>> needs someone
>>> who is better at English than me to look at it / improve it.
>
> well.. how about this small tweak?
>
> This hook takes a @var{mode} for a doloop IV, where @code{mode} 
> is the original mode for the operation.  If the target prefers 
> an alternate @code{mode} for the operation, then this hook 
> should return that mode.  For example, on a 64-bit target, 
> @code{DImode} might be preferred over @code{SImode}.  The 
> original @code{mode} should be returned if that is suitable. 
> Both the original and the returned modes should be 
> @code{MODE_INT}.

Hi Iain,

Thanks a lot! I would nearly use all your words. :) 

This hook takes a @var{mode} for a doloop IV, where @code{mode} is 
the original mode for the operation.  If the target prefers an 
alternate @code{mode} for the operation, then this hook should 
return that mode; otherwise the original @code{mode} should be 
returned.  For example, on a 64-bit target, @code{DImode} might be 
preferred over @code{SImode}.  Both the original and the returned 
modes should be @code{MODE_INT}.

BR,
Jiufu

>
> 0.02GBP only.
> Iain

On 2021-07-15 14:06, Richard Biener wrote:
> On Tue, 13 Jul 2021, Jiufu Guo wrote:
> 
>> Major changes from v1:
>> * Add target hook to query preferred doloop mode.
>> * Recompute doloop iv base from niter under preferred mode.
>> 
>> Currently, doloop.xx variable is using the type as niter which may 
>> shorter
>> than word size.  For some cases, it would be better to use word size 
>> type.
>> For example, on 64bit system, to access 32bit value, subreg maybe 
>> used.
>> Then using 64bit type maybe better for niter if it can be present in
>> both 32bit and 64bit.
>> 
>> This patch add target hook for querg perferred mode for doloop iv.
>> And update doloop iv mode accordingly.
>> 
>> Bootstrap and regtest pass on powerpc64le, is this ok for trunk?
>> 
>> BR.
>> Jiufu
>> 
>> gcc/ChangeLog:
>> 
>> 2021-07-13  Jiufu Guo  <guojiufu@linux.ibm.com>
>> 
>> 	PR target/61837
>> 	* config/rs6000/rs6000.c (TARGET_PREFERRED_DOLOOP_MODE): New hook.
>> 	(rs6000_preferred_doloop_mode): New hook.
>> 	* doc/tm.texi: Regenerated.
>> 	* doc/tm.texi.in: Add hook preferred_doloop_mode.
>> 	* target.def (preferred_doloop_mode): New hook.
>> 	* targhooks.c (default_preferred_doloop_mode): New hook.
>> 	* targhooks.h (default_preferred_doloop_mode): New hook.
>> 	* tree-ssa-loop-ivopts.c (compute_doloop_base_on_mode): New function.
>> 	(add_iv_candidate_for_doloop): Call targetm.preferred_doloop_mode
>> 	and compute_doloop_base_on_mode.
>> 
>> gcc/testsuite/ChangeLog:
>> 
>> 2021-07-13  Jiufu Guo  <guojiufu@linux.ibm.com>
>> 
>> 	PR target/61837
>> 	* gcc.target/powerpc/pr61837.c: New test.
>> ---
>>  gcc/config/rs6000/rs6000.c                 |  9 +++
>>  gcc/doc/tm.texi                            |  4 ++
>>  gcc/doc/tm.texi.in                         |  2 +
>>  gcc/target.def                             |  7 +++
>>  gcc/targhooks.c                            |  8 +++
>>  gcc/targhooks.h                            |  2 +
>>  gcc/testsuite/gcc.target/powerpc/pr61837.c | 16 ++++++
>>  gcc/tree-ssa-loop-ivopts.c                 | 66 
>> +++++++++++++++++++++-
>>  8 files changed, 112 insertions(+), 2 deletions(-)
>>  create mode 100644 gcc/testsuite/gcc.target/powerpc/pr61837.c
>> 
>> diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c
>> index 9a5db63d0ef..444f3c49288 100644
>> --- a/gcc/config/rs6000/rs6000.c
>> +++ b/gcc/config/rs6000/rs6000.c
>> @@ -1700,6 +1700,9 @@ static const struct attribute_spec 
>> rs6000_attribute_table[] =
>>  #undef TARGET_DOLOOP_COST_FOR_ADDRESS
>>  #define TARGET_DOLOOP_COST_FOR_ADDRESS 1000000000
>> 
>> +#undef TARGET_PREFERRED_DOLOOP_MODE
>> +#define TARGET_PREFERRED_DOLOOP_MODE rs6000_preferred_doloop_mode
>> +
>>  #undef TARGET_ATOMIC_ASSIGN_EXPAND_FENV
>>  #define TARGET_ATOMIC_ASSIGN_EXPAND_FENV 
>> rs6000_atomic_assign_expand_fenv
>> 
>> @@ -27867,6 +27870,12 @@ rs6000_predict_doloop_p (struct loop *loop)
>>    return true;
>>  }
>> 
>> +static machine_mode
>> +rs6000_preferred_doloop_mode (machine_mode)
>> +{
>> +  return word_mode;
>> +}
>> +
>>  /* Implement TARGET_CANNOT_SUBSTITUTE_MEM_EQUIV_P.  */
>> 
>>  static bool
>> diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
>> index 2a41ae5fba1..3f5881220f8 100644
>> --- a/gcc/doc/tm.texi
>> +++ b/gcc/doc/tm.texi
>> @@ -11984,6 +11984,10 @@ By default, the RTL loop optimizer does not 
>> use a present doloop pattern for
>>  loops containing function calls or branch on table instructions.
>>  @end deftypefn
>> 
>> +@deftypefn {Target Hook} machine_mode TARGET_PREFERRED_DOLOOP_MODE 
>> (machine_mode @var{mode})
>> +This hook returns a more preferred mode or the @var{mode} itself.
>> +@end deftypefn
>> +
>>  @deftypefn {Target Hook} bool TARGET_LEGITIMATE_COMBINED_INSN 
>> (rtx_insn *@var{insn})
>>  Take an instruction in @var{insn} and return @code{false} if the 
>> instruction
>>  is not appropriate as a combination of two or more instructions.  The
>> diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in
>> index f881cdabe9e..38215149a92 100644
>> --- a/gcc/doc/tm.texi.in
>> +++ b/gcc/doc/tm.texi.in
>> @@ -7917,6 +7917,8 @@ to by @var{ce_info}.
>> 
>>  @hook TARGET_INVALID_WITHIN_DOLOOP
>> 
>> +@hook TARGET_PREFERRED_DOLOOP_MODE
>> +
>>  @hook TARGET_LEGITIMATE_COMBINED_INSN
>> 
>>  @hook TARGET_CAN_FOLLOW_JUMP
>> diff --git a/gcc/target.def b/gcc/target.def
>> index c009671c583..91a96150e50 100644
>> --- a/gcc/target.def
>> +++ b/gcc/target.def
>> @@ -4454,6 +4454,13 @@ loops containing function calls or branch on 
>> table instructions.",
>>   const char *, (const rtx_insn *insn),
>>   default_invalid_within_doloop)
>> 
>> +DEFHOOK
>> +(preferred_doloop_mode,
>> + "This hook returns a more preferred mode or the @var{mode} itself.",
>> + machine_mode,
>> + (machine_mode mode),
>> + default_preferred_doloop_mode)
>> +
>>  /* Returns true for a legitimate combined insn.  */
>>  DEFHOOK
>>  (legitimate_combined_insn,
>> diff --git a/gcc/targhooks.c b/gcc/targhooks.c
>> index 44a1facedcf..eb5190910dc 100644
>> --- a/gcc/targhooks.c
>> +++ b/gcc/targhooks.c
>> @@ -660,6 +660,14 @@ default_predict_doloop_p (class loop *loop 
>> ATTRIBUTE_UNUSED)
>>    return false;
>>  }
>> 
>> +/* By default, just use the input MODE itself.  */
>> +
>> +machine_mode
>> +default_preferred_doloop_mode (machine_mode mode)
>> +{
>> +  return mode;
>> +}
>> +
>>  /* NULL if INSN insn is valid within a low-overhead loop, otherwise 
>> returns
>>     an error message.
>> 
>> diff --git a/gcc/targhooks.h b/gcc/targhooks.h
>> index f70a307d26c..f0560b6ae34 100644
>> --- a/gcc/targhooks.h
>> +++ b/gcc/targhooks.h
>> @@ -88,6 +88,8 @@ extern bool default_fixed_point_supported_p (void);
>>  extern bool default_has_ifunc_p (void);
>> 
>>  extern bool default_predict_doloop_p (class loop *);
>> +extern machine_mode
>> +default_preferred_doloop_mode (machine_mode);
>>  extern const char * default_invalid_within_doloop (const rtx_insn *);
>> 
>>  extern tree default_builtin_vectorized_function (unsigned int, tree, 
>> tree);
>> diff --git a/gcc/testsuite/gcc.target/powerpc/pr61837.c 
>> b/gcc/testsuite/gcc.target/powerpc/pr61837.c
>> new file mode 100644
>> index 00000000000..dc44eb9cb41
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.target/powerpc/pr61837.c
>> @@ -0,0 +1,16 @@
>> +/* { dg-do compile } */
>> +/* { dg-options "-O2" } */
>> +void foo(int *p1, long *p2, int s)
>> +{
>> +  int n, v, i;
>> +
>> +  v = 0;
>> +  for (n = 0; n <= 100; n++) {
>> +     for (i = 0; i < s; i++)
>> +        if (p2[i] == n)
>> +           p1[i] = v;
>> +     v += 88;
>> +  }
>> +}
>> +
>> +/* { dg-final { scan-assembler-not {\mrldicl\M} } } */
>> diff --git a/gcc/tree-ssa-loop-ivopts.c b/gcc/tree-ssa-loop-ivopts.c
>> index 12a8a49a307..92767a09b6c 100644
>> --- a/gcc/tree-ssa-loop-ivopts.c
>> +++ b/gcc/tree-ssa-loop-ivopts.c
>> @@ -5657,6 +5657,56 @@ relate_compare_use_with_all_cands (struct 
>> ivopts_data *data)
>>      }
>>  }
>> 
>> +/* If PREFERRED_MODE is suitable and profitable, use the preferred
>> +   PREFERRED_MODE to compute doloop iv base from niter: base = niter 
>> + 1.  */
>> +
>> +static tree
>> +compute_doloop_base_on_mode (machine_mode preferred_mode, tree niter,
>> +			     const widest_int &iterations_max)
>> +{
>> +  tree ntype = TREE_TYPE (niter);
>> +  tree pref_type = lang_hooks.types.type_for_mode (preferred_mode, 
>> 1);
> 
> It's unlikely but type_for_mode can return NULL, so you shouldn't
> assert but fall back to using the original type.  The assert for
> TYPE_UNSIGNED is superfluous - you asked for an unsigned type already.

Thanks!

Yes, it would be better to check pref_type instead assert.
And, assert on TYPE_UNSIGNED (ntype) seems not required, the code takes 
care
of the max value of types already.

> 
> Otherwise the IVOPTs changes and the new target hook look OK, please
> address Seghers comments though.

I will send out an updated patch according to these comments!

Thanks for your review!

BR,
Jiufu

> 
> Thanks,
> Richard.
> 
>> +  gcc_assert (pref_type && TYPE_UNSIGNED (ntype));
>> +
>> +  int prec = TYPE_PRECISION (ntype);
>> +  int pref_prec = TYPE_PRECISION (pref_type);
>> +
>> +  tree base;
>> +
>> +  /* Check if the PREFERRED_MODED is able to present niter.  */
>> +  if (pref_prec > prec
>> +      || wi::ltu_p (iterations_max,
>> +		    widest_int::from (wi::max_value (pref_prec, UNSIGNED),
>> +				      UNSIGNED)))
>> +    {
>> +      /* No wrap, it is safe to use preferred type after niter + 1.  
>> */
>> +      if (wi::ltu_p (iterations_max,
>> +		     widest_int::from (wi::max_value (prec, UNSIGNED),
>> +				       UNSIGNED)))
>> +	{
>> +	  /* This could help to optimize "-1 +1" pair when niter looks
>> +	     like "n-1": n is in original mode.  "base = (n - 1) + 1"
>> +	     in PREFERRED_MODED: it could be base = (PREFERRED_TYPE)n.  */
>> +	  base = fold_build2 (PLUS_EXPR, ntype, unshare_expr (niter),
>> +			      build_int_cst (ntype, 1));
>> +	  base = fold_convert (pref_type, base);
>> +	}
>> +
>> +      /* To avoid wrap, need fold niter to preferred type before plus 
>> 1.  */
>> +      else
>> +	{
>> +	  niter = fold_convert (pref_type, niter);
>> +	  base = fold_build2 (PLUS_EXPR, pref_type, unshare_expr (niter),
>> +			      build_int_cst (pref_type, 1));
>> +	}
>> +    }
>> +  else
>> +    base = fold_build2 (PLUS_EXPR, ntype, unshare_expr (niter),
>> +			build_int_cst (ntype, 1));
>> +  return base;
>> +}
>> +
>>  /* Add one doloop dedicated IV candidate:
>>       - Base is (may_be_zero ? 1 : (niter + 1)).
>>       - Step is -1.  */
>> @@ -5688,8 +5738,20 @@ add_iv_candidate_for_doloop (struct ivopts_data 
>> *data)
>>  	return;
>>      }
>> 
>> -  tree base = fold_build2 (PLUS_EXPR, ntype, unshare_expr (niter),
>> -			   build_int_cst (ntype, 1));
>> +  machine_mode mode = TYPE_MODE (ntype);
>> +  machine_mode pref_mode = targetm.preferred_doloop_mode (mode);
>> +
>> +  tree base;
>> +  if (mode != pref_mode)
>> +    {
>> +      base = compute_doloop_base_on_mode (pref_mode, niter, 
>> niter_desc->max);
>> +      ntype = TREE_TYPE (base);
>> +    }
>> +  else
>> +    base = fold_build2 (PLUS_EXPR, ntype, unshare_expr (niter),
>> +			build_int_cst (ntype, 1));
>> +
>> +
>>    add_candidate (data, base, build_int_cst (ntype, -1), true, NULL, 
>> NULL, true);
>>  }
>> 
>>