Add 'dg-note', 'dg-lto-note' (was: Add 'dg-note' next to 'dg-optimized', 'dg-missed')

[Thomas Schwinge <thomas@codesourcery.com>]

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Hi!

On 2020-11-30T12:28:31-0700, Jeff Law via Gcc-patches <gcc-patches@gcc.gnu.org> wrote:
> On 11/24/20 2:53 AM, Thomas Schwinge wrote:
>> On 2020-11-06T10:26:46+0100, I wrote:
>>> On 2018-09-25T16:00:14-0400, David Malcolm <dmalcolm@redhat.com> wrote:
>>>> As noted at Cauldron, dumpfile.c currently emits "note: " for all kinds
>>>> of dump message, so that (after filtering) there's no distinction between
>>>> MSG_OPTIMIZED_LOCATIONS vs MSG_NOTE vs MSG_MISSED_OPTIMIZATION in the
>>>> textual output.
>>>>
>>>> This patch changes dumpfile.c so that the "note: " varies to show
>>>> which MSG_* was used, with the string prefix matching that used for
>>>> filtering in -fopt-info, hence e.g.
>>>>   directive_unroll_3.f90:24:0: optimized: loop unrolled 7 times
>>>> and:
>>>>   pr19210-1.c:24:3: missed: missed loop optimization: niters analysis ends up with assumptions.
>>> (However, 'MSG_NOTE'/'note: ' also still remains used for "general
>>> optimization info".)

Well, and of course, 'note: ' prefixes have also "forever" been used for
'inform' etc. diagnostics; so my change here much more relates to
'dg-message', 'dg-warning', 'dg-error' rather than 'dg-optimized',
'dg-missed'.  ;-)

>>>> The patch adds "dg-optimized" and "dg-missed" directives
>>>> --- a/gcc/testsuite/lib/gcc-dg.exp
>>>> +++ b/gcc/testsuite/lib/gcc-dg.exp
>>>> +# Handle output from -fopt-info for MSG_OPTIMIZED_LOCATIONS:
>>>> +# a successful optimization.
>>>> +
>>>> +proc dg-optimized { args } {
>>>> +    # Make this variable available here and to the saved proc.
>>>> +    upvar dg-messages dg-messages
>>>> +
>>>> +    process-message saved-dg-error "optimized: " "$args"
>>>> +}
>>>> +
>>>> +# Handle output from -fopt-info for MSG_MISSED_OPTIMIZATION:
>>>> +# a missed optimization.
>>>> +
>>>> +proc dg-missed { args } {
>>>> +    # Make this variable available here and to the saved proc.
>>>> +    upvar dg-messages dg-messages
>>>> +
>>>> +    process-message saved-dg-error "missed: " "$args"
>>>> +}
>>>> +
>>>
>>> Next to these, I'm proposing to add 'dg-note', see attached "[WIP] Add
>>> 'dg-note' next to 'dg-optimized'", which may be used instead of generic
>>> 'dg-message' (which in current uses in testcases often doesn't scan for
>>> the 'note: ' prefix, by the way).
>>>
>>> The proposed 'dg-note' has the additional property that "if dg-note is
>>> used once, [notes] must *all* be handled explicitly".  The rationale is
>>> that either you're not interested in notes at all (default behavior of
>>> pruning all notes), but often, when you're interested in one note, you're
>>> in fact interested in all notes, and especially interested if
>>> *additional* notes appear over time, as GCC evolves.  It seemed somewhat
>>> useful, but I'm not insisting on coupling the disabling of notes pruning
>>> on 'dg-note' usage, so if anyone feels strongly about that, please speak
>>> up.

(No comments received.)

> I think this is generally fine with the proper doc updates.

ACK, thanks; done.

>>> TODO 'gcc/testsuite/lib/lto.exp' change necessary/desirable?
>>>
>>> The latter got added in commit 824721f0905478ebc39e6a295cc8e95c22fa9d17
>>> "lto, testsuite: Fix ICE in -Wodr (PR lto/83121)".  David, do you happen
>>> to have an opinion on that one?

> I wouldn't
> think we'd want/need to treat LTO differently, so I'm not so sure about
> that specific hunk.

As it should turn out -- of course ;-) -- LTO does need some special
care; added, plus a few testcases adapted, too.

I've pushed "Add 'dg-note', 'dg-lto-note'" to master branch in commit
03eb779141a29f96600cd46904b88a33c4b49a66, see attached.


Grüße
 Thomas


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From 03eb779141a29f96600cd46904b88a33c4b49a66 Mon Sep 17 00:00:00 2001
From: Thomas Schwinge <thomas@codesourcery.com>
Date: Thu, 6 May 2021 11:59:42 +0200
Subject: [PATCH] Add 'dg-note', 'dg-lto-note'

That's 'dg-message "note: [...]"' with a twist: inhibit default notes pruning,
such that "if 'dg-note' is used at least once in a testcase, [notes] are not
pruned and instead must *all* be handled explicitly".

The rationale is that either you're not interested in notes at all (default
behavior of pruning all notes), but often, when you're interested in one note,
you're in fact interested in all notes, and especially interested if
*additional* notes appear over time, as GCC evolves.

	gcc/testsuite/
	* lib/gcc-dg.exp: Implement 'dg-note'.
	* lib/prune.exp: Likewise.
	* gcc.dg/vect/nodump-vect-opt-info-2.c: Use 'dg-note', and
	'dg-prune-output "note: ".
	* gfortran.dg/goacc/routine-external-level-of-parallelism-2.f: Use
	'dg-note', match up additional notes, one class of them with
	XFAILed 'dg-bogus'.
	* lib/lto.exp: Implement 'dg-lto-note'.
	* g++.dg/lto/odr-1_0.C: Use 'dg-lto-note', match up additional
	notes.
	* g++.dg/lto/odr-1_1.C: Likewise.
	* g++.dg/lto/odr-2_1.C: Likewise.
	libstdc++-v3/
	* testsuite/lib/prune.exp: Add note about 'dg-note'.
	gcc/
	* doc/sourcebuild.texi: Document 'dg-note'.
---
 gcc/doc/sourcebuild.texi                      | 22 +++++++++++--
 gcc/testsuite/g++.dg/lto/odr-1_0.C            |  4 ++-
 gcc/testsuite/g++.dg/lto/odr-1_1.C            |  9 +++---
 gcc/testsuite/g++.dg/lto/odr-2_1.C            |  2 +-
 .../gcc.dg/vect/nodump-vect-opt-info-2.c      |  4 ++-
 .../routine-external-level-of-parallelism-2.f | 26 +++++++++++++++
 gcc/testsuite/lib/gcc-dg.exp                  | 32 +++++++++++++++++++
 gcc/testsuite/lib/lto.exp                     | 22 ++++++++++---
 gcc/testsuite/lib/prune.exp                   |  7 ++--
 libstdc++-v3/testsuite/lib/prune.exp          |  2 ++
 10 files changed, 114 insertions(+), 16 deletions(-)

diff --git a/gcc/doc/sourcebuild.texi b/gcc/doc/sourcebuild.texi
index ceb6b995283..ed811d103a5 100644
--- a/gcc/doc/sourcebuild.texi
+++ b/gcc/doc/sourcebuild.texi
@@ -1217,6 +1217,21 @@ If there is no message for that line or if the text of that message is
 not matched by @var{regexp} then the check fails and @var{comment} is
 included in the @code{FAIL} message.
 
+@item @{ dg-note @var{regexp} [@var{comment} [@{ target/xfail @var{selector} @} [@var{line}] ]] @}
+The line is expected to get a @samp{note} message.
+If there is no message for that line or if the text of that message is
+not matched by @var{regexp} then the check fails and @var{comment} is
+included in the @code{FAIL} message.
+
+By default, any @emph{excess} @samp{note} messages are pruned, meaning
+their appearance doesn't trigger @emph{excess errors}.
+However, if @samp{dg-note} is used at least once in a testcase,
+they're not pruned and instead must @emph{all} be handled explicitly.
+Thus, if looking for just single instances of messages with
+@samp{note: } prefixes without caring for all of them, use
+@samp{dg-message "note: [@dots{}]"} instead of @samp{dg-note}, or use
+@samp{dg-note} together with @samp{dg-prune-output "note: "}.
+
 @item @{ dg-bogus @var{regexp} [@var{comment} [@{ target/xfail @var{selector} @} [@var{line}] ]] @}
 This DejaGnu directive appears on a source line that should not get a
 message matching @var{regexp}, or else specifies the source line
@@ -1227,7 +1242,8 @@ targets.
 @item @{ dg-line @var{linenumvar} @}
 This DejaGnu directive sets the variable @var{linenumvar} to the line number of
 the source line.  The variable @var{linenumvar} can then be used in subsequent
-@code{dg-error}, @code{dg-warning}, @code{dg-message} and @code{dg-bogus}
+@code{dg-error}, @code{dg-warning}, @code{dg-message}, @code{dg-note}
+and @code{dg-bogus}
 directives.  For example:
 
 @smallexample
@@ -1239,7 +1255,9 @@ float a; /* @{ dg-error "conflicting types of" @} */
 @item @{ dg-excess-errors @var{comment} [@{ target/xfail @var{selector} @}] @}
 This DejaGnu directive indicates that the test is expected to fail due
 to compiler messages that are not handled by @samp{dg-error},
-@samp{dg-warning} or @samp{dg-bogus}.  For this directive @samp{xfail}
+@samp{dg-warning}, @code{dg-message}, @samp{dg-note} or
+@samp{dg-bogus}.
+For this directive @samp{xfail}
 has the same effect as @samp{target}.
 
 @item @{ dg-prune-output @var{regexp} @}
diff --git a/gcc/testsuite/g++.dg/lto/odr-1_0.C b/gcc/testsuite/g++.dg/lto/odr-1_0.C
index 6fff88844c3..318a047cb70 100644
--- a/gcc/testsuite/g++.dg/lto/odr-1_0.C
+++ b/gcc/testsuite/g++.dg/lto/odr-1_0.C
@@ -1,8 +1,10 @@
 // PR c++/82414
 // { dg-lto-do link }
 enum vals {aa,cc}; // { dg-lto-warning "6: type 'vals' violates the C\\+\\+ One Definition Rule" }
+// { dg-lto-note "name 'cc' differs from name 'bb' defined in another translation unit" "" { target *-*-* } .-1 }
 struct a { // { dg-lto-warning "8: type 'struct a' violates the C\\+\\+ One Definition Rule" }
-  struct b *ptr; // { dg-lto-message "13: the first difference of corresponding definitions is field 'ptr'" }
+  struct b *ptr; // { dg-lto-note "13: the first difference of corresponding definitions is field 'ptr'" }
+  // { dg-lto-note "the incompatible type defined in another translation unit" "" { target *-*-* } .-1 }
   enum vals vals;
 };
 void test(struct a *a)
diff --git a/gcc/testsuite/g++.dg/lto/odr-1_1.C b/gcc/testsuite/g++.dg/lto/odr-1_1.C
index 494436a46c6..a57bb3898aa 100644
--- a/gcc/testsuite/g++.dg/lto/odr-1_1.C
+++ b/gcc/testsuite/g++.dg/lto/odr-1_1.C
@@ -1,9 +1,10 @@
 namespace {
-  struct b; // { dg-lto-message "type 'struct b' defined in anonymous namespace cannot match across the translation unit boundary" }
+  struct b; // { dg-lto-note "type 'struct b' defined in anonymous namespace cannot match across the translation unit boundary" }
  }
-enum vals {aa,bb,cc}; // { dg-lto-message "an enum with different value name is defined in another translation unit" }
-struct a { // { dg-lto-message "a different type is defined in another translation unit" }
-  struct b *ptr; // { dg-lto-message "a field of same name but different type is defined in another translation unit" }
+enum vals {aa,bb,cc}; // { dg-lto-note "an enum with different value name is defined in another translation unit" }
+// { dg-lto-note "mismatching definition" "" { target *-*-* } .-1 }
+struct a { // { dg-lto-note "a different type is defined in another translation unit" }
+  struct b *ptr; // { dg-lto-note "a field of same name but different type is defined in another translation unit" }
   enum vals vals;
 } a;
 void test(struct a *);
diff --git a/gcc/testsuite/g++.dg/lto/odr-2_1.C b/gcc/testsuite/g++.dg/lto/odr-2_1.C
index f384ae893b7..23cfccc241b 100644
--- a/gcc/testsuite/g++.dg/lto/odr-2_1.C
+++ b/gcc/testsuite/g++.dg/lto/odr-2_1.C
@@ -1,4 +1,4 @@
-class a { // { dg-lto-message "a different type is defined in another translation unit" }
+class a { // { dg-lto-note "a different type is defined in another translation unit" }
   int *b() const;
 };
 int *a::b() const { return 0; }
diff --git a/gcc/testsuite/gcc.dg/vect/nodump-vect-opt-info-2.c b/gcc/testsuite/gcc.dg/vect/nodump-vect-opt-info-2.c
index 23a3b39fbb3..bcdf7f07671 100644
--- a/gcc/testsuite/gcc.dg/vect/nodump-vect-opt-info-2.c
+++ b/gcc/testsuite/gcc.dg/vect/nodump-vect-opt-info-2.c
@@ -3,7 +3,9 @@
 
 extern void accumulate (int x, int *a);
 
-int test_missing_function_defn (int *arr, int n) /* { dg-message "vectorized 0 loops in function" } */
+int test_missing_function_defn (int *arr, int n) /* { dg-note "5: vectorized 0 loops in function" } */
+/* { dg-prune-output "note: " } as we're not interested in matching any further
+   notes.  */
 {
   int sum = 0;
   for (int i = 0; i < n; ++i) /* { dg-missed "21: couldn't vectorize loop" } */
diff --git a/gcc/testsuite/gfortran.dg/goacc/routine-external-level-of-parallelism-2.f b/gcc/testsuite/gfortran.dg/goacc/routine-external-level-of-parallelism-2.f
index 0e8dfb19e2b..04d507fef9a 100644
--- a/gcc/testsuite/gfortran.dg/goacc/routine-external-level-of-parallelism-2.f
+++ b/gcc/testsuite/gfortran.dg/goacc/routine-external-level-of-parallelism-2.f
@@ -22,6 +22,8 @@
 ! { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 }
          do j = 1, n
             call workerr (a, n) ! { dg-message "optimized: assigned OpenACC worker vector loop parallelism" }
+! { dg-bogus "note: routine 'workerr' declared here" "TODO" { xfail { ! offloading_enabled } } .-1 }
+! { dg-bogus "note: routine 'workerr_' declared here" "TODO" { xfail offloading_enabled } .-2 }
          end do
       end do
 !$acc end parallel loop
@@ -30,9 +32,12 @@
 ! { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 }
       do i = 1, n
 !$acc loop gang ! { dg-message "optimized: assigned OpenACC gang loop parallelism" }
+! { dg-note "containing loop here" "" { target *-*-* } .-1 }
          do j = 1, n
             call gangr (a, n) ! { dg-message "optimized: assigned OpenACC worker vector loop parallelism" }
 ! { dg-error "routine call uses same OpenACC parallelism as containing loop" "" { target *-*-* } .-1 }
+! { dg-bogus "note: routine 'gangr' declared here" "TODO" { xfail { ! offloading_enabled } } .-2 }
+! { dg-bogus "note: routine 'gangr_' declared here" "TODO" { xfail offloading_enabled } .-3 }
          end do
       end do
 !$acc end parallel loop
@@ -83,6 +88,7 @@
 !$acc end parallel loop
 
 !$acc parallel loop gang ! { dg-message "optimized: assigned OpenACC gang loop parallelism" }
+! { dg-note "containing loop here" "" { target *-*-* } .-1 }
       do i = 1, n
          call gangr (a, n) ! { dg-message "optimized: assigned OpenACC worker vector loop parallelism" }
 ! { dg-error "routine call uses same OpenACC parallelism as containing loop" "" { target *-*-* } .-1 }
@@ -90,6 +96,7 @@
 !$acc end parallel loop
 
 !$acc parallel loop worker ! { dg-message "optimized: assigned OpenACC worker loop parallelism" }
+! { dg-note "containing loop here" "" { target *-*-* } .-1 }
       do i = 1, n
          call gangr (a, n) ! { dg-message "optimized: assigned OpenACC gang vector loop parallelism" }
 ! { dg-error "routine call uses same OpenACC parallelism as containing loop" "" { target *-*-* } .-1 }
@@ -97,6 +104,7 @@
 !$acc end parallel loop
 
 !$acc parallel loop vector ! { dg-message "optimized: assigned OpenACC vector loop parallelism" }
+! { dg-note "containing loop here" "" { target *-*-* } .-1 }
       do i = 1, n
          call gangr (a, n) ! { dg-message "optimized: assigned OpenACC gang worker loop parallelism" }
 ! { dg-error "routine call uses same OpenACC parallelism as containing loop" "" { target *-*-* } .-1 }
@@ -126,6 +134,7 @@
 !$acc end parallel loop
 
 !$acc parallel loop worker ! { dg-message "optimized: assigned OpenACC worker loop parallelism" }
+! { dg-note "containing loop here" "" { target *-*-* } .-1 }
       do i = 1, n
          call workerr (a, n) ! { dg-message "optimized: assigned OpenACC vector loop parallelism" }
 ! { dg-error "routine call uses same OpenACC parallelism as containing loop" "" { target *-*-* } .-1 }
@@ -133,6 +142,7 @@
 !$acc end parallel loop
 
 !$acc parallel loop vector ! { dg-message "optimized: assigned OpenACC vector loop parallelism" }
+! { dg-note "containing loop here" "" { target *-*-* } .-1 }
       do i = 1, n
          call workerr (a, n) ! { dg-message "optimized: assigned OpenACC worker loop parallelism" }
 ! { dg-error "routine call uses same OpenACC parallelism as containing loop" "" { target *-*-* } .-1 }
@@ -152,6 +162,8 @@
 !$acc parallel loop ! { dg-message "optimized: assigned OpenACC gang worker loop parallelism" }
       do i = 1, n
          call vectorr (a, n) ! { dg-message "optimized: assigned OpenACC vector loop parallelism" }
+! { dg-bogus "note: routine 'vectorr' declared here" "TODO" { xfail { ! offloading_enabled } } .-1 }
+! { dg-bogus "note: routine 'vectorr_' declared here" "TODO" { xfail offloading_enabled } .-2 }
       end do
 !$acc end parallel loop
 
@@ -168,6 +180,7 @@
 !$acc end parallel loop
 
 !$acc parallel loop vector ! { dg-message "optimized: assigned OpenACC vector loop parallelism" }
+! { dg-note "containing loop here" "" { target *-*-* } .-1 }
       do i = 1, n
          call vectorr (a, n) ! { dg-message "optimized: assigned OpenACC seq loop parallelism" }
 ! { dg-error "routine call uses same OpenACC parallelism as containing loop" "" { target *-*-* } .-1 }
@@ -201,6 +214,8 @@
 ! { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 }
          do j = 1, n
             a(i) = workerf (a, n) ! { dg-message "optimized: assigned OpenACC worker vector loop parallelism" }
+! { dg-bogus "note: routine 'workerf' declared here" "TODO" { xfail { ! offloading_enabled } } .-1 }
+! { dg-bogus "note: routine 'workerf_' declared here" "TODO" { xfail offloading_enabled } .-2 }
          end do
       end do
 !$acc end parallel loop
@@ -209,9 +224,12 @@
 ! { dg-warning "insufficient partitioning available to parallelize loop" "" { target *-*-* } .-1 }
       do i = 1, n
 !$acc loop gang ! { dg-message "optimized: assigned OpenACC gang loop parallelism" }
+! { dg-note "containing loop here" "" { target *-*-* } .-1 }
          do j = 1, n
             a(i) = gangf (a, n) ! { dg-message "optimized: assigned OpenACC worker vector loop parallelism" }
 ! { dg-error "routine call uses same OpenACC parallelism as containing loop" "" { target *-*-* } .-1 }
+! { dg-bogus "note: routine 'gangf' declared here" "TODO" { xfail { ! offloading_enabled } } .-2 }
+! { dg-bogus "note: routine 'gangf_' declared here" "TODO" { xfail offloading_enabled } .-3 }
          end do
       end do
 !$acc end parallel loop
@@ -262,6 +280,7 @@
 !$acc end parallel loop
 
 !$acc parallel loop gang ! { dg-message "optimized: assigned OpenACC gang loop parallelism" }
+! { dg-note "containing loop here" "" { target *-*-* } .-1 }
       do i = 1, n
          a(i) = gangf (a, n) ! { dg-message "optimized: assigned OpenACC worker vector loop parallelism" }
 ! { dg-error "routine call uses same OpenACC parallelism as containing loop" "" { target *-*-* } .-1 }
@@ -269,6 +288,7 @@
 !$acc end parallel loop
 
 !$acc parallel loop worker ! { dg-message "optimized: assigned OpenACC worker loop parallelism" }
+! { dg-note "containing loop here" "" { target *-*-* } .-1 }
       do i = 1, n
          a(i) = gangf (a, n) ! { dg-message "optimized: assigned OpenACC gang vector loop parallelism" }
 ! { dg-error "routine call uses same OpenACC parallelism as containing loop" "" { target *-*-* } .-1 }
@@ -276,6 +296,7 @@
 !$acc end parallel loop
 
 !$acc parallel loop vector ! { dg-message "optimized: assigned OpenACC vector loop parallelism" }
+! { dg-note "containing loop here" "" { target *-*-* } .-1 }
       do i = 1, n
          a(i) = gangf (a, n) ! { dg-message "optimized: assigned OpenACC gang worker loop parallelism" }
 ! { dg-error "routine call uses same OpenACC parallelism as containing loop" "" { target *-*-* } .-1 }
@@ -305,6 +326,7 @@
 !$acc end parallel loop
 
 !$acc parallel loop worker ! { dg-message "optimized: assigned OpenACC worker loop parallelism" }
+! { dg-note "containing loop here" "" { target *-*-* } .-1 }
       do i = 1, n
          a(i) = workerf (a, n) ! { dg-message "optimized: assigned OpenACC vector loop parallelism" }
 ! { dg-error "routine call uses same OpenACC parallelism as containing loop" "" { target *-*-* } .-1 }
@@ -312,6 +334,7 @@
 !$acc end parallel loop
 
 !$acc parallel loop vector ! { dg-message "optimized: assigned OpenACC vector loop parallelism" }
+! { dg-note "containing loop here" "" { target *-*-* } .-1 }
       do i = 1, n
          a(i) = workerf (a, n) ! { dg-message "optimized: assigned OpenACC worker loop parallelism" }
 ! { dg-error "routine call uses same OpenACC parallelism as containing loop" "" { target *-*-* } .-1 }
@@ -331,6 +354,8 @@
 !$acc parallel loop ! { dg-message "optimized: assigned OpenACC gang worker loop parallelism" }
       do i = 1, n
          a(i) = vectorf (a, n) ! { dg-message "optimized: assigned OpenACC vector loop parallelism" }
+! { dg-bogus "note: routine 'vectorf' declared here" "TODO" { xfail { ! offloading_enabled } } .-1 }
+! { dg-bogus "note: routine 'vectorf_' declared here" "TODO" { xfail offloading_enabled } .-2 }
       end do
 !$acc end parallel loop
 
@@ -347,6 +372,7 @@
 !$acc end parallel loop
 
 !$acc parallel loop vector ! { dg-message "optimized: assigned OpenACC vector loop parallelism" }
+! { dg-note "containing loop here" "" { target *-*-* } .-1 }
       do i = 1, n
          a(i) = vectorf (a, n) ! { dg-message "optimized: assigned OpenACC seq loop parallelism" }
 ! { dg-error "routine call uses same OpenACC parallelism as containing loop" "" { target *-*-* } .-1 }
diff --git a/gcc/testsuite/lib/gcc-dg.exp b/gcc/testsuite/lib/gcc-dg.exp
index e48a184f991..fce0989cd9c 100644
--- a/gcc/testsuite/lib/gcc-dg.exp
+++ b/gcc/testsuite/lib/gcc-dg.exp
@@ -1012,6 +1012,8 @@ if { [info procs saved-dg-test] == [list] } {
 	    }
 	    unset save_linenr_varnames
 	}
+
+	initialize_prune_notes
     }
 
     proc dg-test { args } {
@@ -1245,6 +1247,36 @@ proc dg-missed { args } {
     process-message saved-dg-warning "missed:" "$args"
 }
 
+# Look for messages with 'note: ' prefixes.
+# In addition to standard compiler diagnostics ('DK_NOTE', 'inform' functions,
+# "for additional details on an error message"),
+# this also includes output from '-fopt-info' for 'MSG_NOTE':
+# a general optimization info.
+# By default, any *excess* notes are pruned, meaning their appearance doesn't
+# trigger *excess errors*.  However, if 'dg-note' is used at least once in a
+# testcase, they're not pruned and instead must *all* be handled explicitly.
+# Thus, if looking for just single instances of messages with 'note: ' prefixes
+# without caring for all of them, use 'dg-message "note: [...]"' instead of
+# 'dg-note', or use 'dg-note' together with 'dg-prune-output "note: "'.
+
+variable prune_notes
+
+proc initialize_prune_notes { } {
+    global prune_notes
+    set prune_notes 1
+}
+
+initialize_prune_notes
+
+proc dg-note { args } {
+    upvar dg-messages dg-messages
+
+    global prune_notes
+    set prune_notes 0
+
+    process-message saved-dg-warning "note:" "$args"
+}
+
 # Check the existence of a gdb in the path, and return true if there
 # is one.
 #
diff --git a/gcc/testsuite/lib/lto.exp b/gcc/testsuite/lib/lto.exp
index 77919e8443b..d0e0dc60138 100644
--- a/gcc/testsuite/lib/lto.exp
+++ b/gcc/testsuite/lib/lto.exp
@@ -161,9 +161,13 @@ proc lto_prune_warns { text } {
 
     # Ignore missing jobserver for tests that do more than 1 LTRANS unit
     regsub -all "(^|\n)\[^\n\]*: warning: using serial compilation of \[^\n\]*" $text "" text
+    regsub -all "(^|\n)\[^\n\]*: note: see the \[^\n\]*'-flto' option documentation\[^\n\]* for more information" $text "" text
 
-    # Ignore informational notes.
-    regsub -all "(^|\n)\[^\n\]*: note: \[^\n\]*" $text "" text
+    global prune_notes
+    if { $prune_notes } {
+	# Ignore informational notes.
+	regsub -all "(^|\n)\[^\n\]*: note: \[^\n\]*" $text "" text
+    }
 
     verbose "lto_prune_warns: exit: $text" 2
 
@@ -390,8 +394,8 @@ proc lto-can-handle-directive { op } {
     # A list of directives to recognize, and a list of directives
     # to remap them to.
     # For example, "dg-lto-warning" is implemented by calling "dg-warning".
-    set directives { dg-lto-warning dg-lto-message }
-    set remapped_directives { dg-warning dg-message }
+    set directives { dg-lto-warning dg-lto-message dg-lto-note }
+    set remapped_directives { dg-warning dg-message dg-note }
 
     set idx [lsearch -exact $directives $cmd]
     if { $idx != -1 } {
@@ -597,7 +601,7 @@ proc lto-get-options { src } {
 #
 # SRC1 is the full pathname of the main file of the testcase.
 # SID identifies a test suite in the names of temporary files.
-proc lto-execute { src1 sid } {
+proc lto-execute-1 { src1 sid } {
     global srcdir tmpdir
     global lto_option_list
     global tool
@@ -811,6 +815,14 @@ proc lto-execute { src1 sid } {
     }
 }
 
+proc lto-execute { src1 sid } {
+    lto-execute-1 $src1 $sid
+
+    # LTO testing doesn't use 'dg-runtest'/'dg-test', and thus doesn't call
+    # 'cleanup-after-saved-dg-test', so we have to clean up manually.
+    initialize_prune_notes
+}
+
 # Call pass if object readelf is ok, otherwise fail.
 # example: /* { dg-final { object-readelf Tag_ABI_enum_size int} } */
 proc object-readelf { args } {
diff --git a/gcc/testsuite/lib/prune.exp b/gcc/testsuite/lib/prune.exp
index 2809f88b16f..91f165bec38 100644
--- a/gcc/testsuite/lib/prune.exp
+++ b/gcc/testsuite/lib/prune.exp
@@ -54,8 +54,11 @@ proc prune_gcc_output { text } {
     regsub -all "(^|\n)\[ \]+from \[^\n\]*" $text "" text
     regsub -all "(^|\n)(In|of) module( \[^\n \]*,)? imported at \[^\n\]*" $text "" text
 
-    # Ignore informational notes.
-    regsub -all "(^|\n)\[^\n\]*: note: \[^\n\]*" $text "" text
+    global prune_notes
+    if { $prune_notes } {
+	# Ignore informational notes.
+	regsub -all "(^|\n)\[^\n\]*: note: \[^\n\]*" $text "" text
+    }
 
     # Ignore harmless -fpic warnings.
     regsub -all "(^|\n)\[^\n\]*: warning: -f(pic|PIC) ignored for target\[^\n\]*" $text "" text
diff --git a/libstdc++-v3/testsuite/lib/prune.exp b/libstdc++-v3/testsuite/lib/prune.exp
index 45c77d210d7..fd4a0ac7f97 100644
--- a/libstdc++-v3/testsuite/lib/prune.exp
+++ b/libstdc++-v3/testsuite/lib/prune.exp
@@ -52,6 +52,8 @@ proc libstdc++-dg-prune { system text } {
     regsub -all "(^|\n)\[ \t\]*from \[^\n\]*" $text "" text
 
     # Ignore informational notes.
+    #TODO As this isn't even using 'gcc-dg.exp', cannot consider its
+    # 'variable prune_notes' (for 'dg-note') here.
     regsub -all "(^|\n)\[^\n\]*: note: \[^\n\]*" $text "" text
 
     # Ignore errata warning from IA64 assembler.
-- 
2.30.2