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* [gcc r11-2872] dwarf2out: Fix up dwarf2out_next_real_insn caching [PR96729]
@ 2020-08-26 8:30 Jakub Jelinek
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From: Jakub Jelinek @ 2020-08-26 8:30 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:ca1afa261d03c9343dff1208325f87d9ba69ec7a
commit r11-2872-gca1afa261d03c9343dff1208325f87d9ba69ec7a
Author: Jakub Jelinek <jakub@redhat.com>
Date: Wed Aug 26 10:30:15 2020 +0200
dwarf2out: Fix up dwarf2out_next_real_insn caching [PR96729]
The addition of NOTE_INSN_BEGIN_STMT and NOTE_INSN_INLINE_ENTRY notes
reintroduced quadratic behavior into dwarf2out_var_location.
This function needs to know the next real instruction to which the var
location note applies, but the way final_scan_insn is called outside of
final.c main loop doesn't make it easy to look up the next real insn in
there (and for non-dwarf it is even useless). Usually next real insn is
only a few notes away, but we can have hundreds of thousands of consecutive
notes only followed by a real insn. dwarf2out_var_location to avoid the
quadratic behavior contains a cache, it remembers the next note and when it
is called again on that loc_note, it can use the previously computed
dwarf2out_next_real_insn result, rather than walking the insn chain once
again. But, for NOTE_INSN_{BEGIN_STMT,INLINE_ENTRY} dwarf2out_var_location
is not called while the code puts into the cache those notes, which means if
we have e.g. in the worst case NOTE_INSN_VAR_LOCATION and
NOTE_INSN_BEGIN_STMT notes alternating, the cache is not really used.
The following patch fixes it by looking up the next NOTE_INSN_VAR_LOCATION
if any. While the lookup could be perhaps done together with looking for
the next real insn once (e.g. in dwarf2out_next_real_insn or its copy),
there are other dwarf2out_next_real_insn callers which don't need/want that
behavior and if there are more than two NOTE_INSN_VAR_LOCATION notes
followed by the same real insn, we need to do that "find next
NOTE_INSN_VAR_LOCATION" walk anyway.
On the testcase from the PR this patch speeds it 2.8times, from 0m0.674s
to 0m0.236s (why it takes for the reporter more than 60s is unknown).
2020-08-26 Jakub Jelinek <jakub@redhat.com>
PR debug/96729
* dwarf2out.c (dwarf2out_next_real_insn): Adjust function comment.
(dwarf2out_var_location): Look for next_note only if next_real is
non-NULL, in that case look for the first non-deleted
NOTE_INSN_VAR_LOCATION between loc_note and next_real, if any.
Diff:
---
gcc/dwarf2out.c | 36 ++++++++++++++++++++----------------
1 file changed, 20 insertions(+), 16 deletions(-)
diff --git a/gcc/dwarf2out.c b/gcc/dwarf2out.c
index 6b03ff85f99..b6ab49bb548 100644
--- a/gcc/dwarf2out.c
+++ b/gcc/dwarf2out.c
@@ -27204,7 +27204,7 @@ static bool maybe_at_text_label_p = true;
/* One above highest N where .LVLN label might be equal to .Ltext0 label. */
static unsigned int first_loclabel_num_not_at_text_label;
-/* Look ahead for a real insn, or for a begin stmt marker. */
+/* Look ahead for a real insn. */
static rtx_insn *
dwarf2out_next_real_insn (rtx_insn *loc_note)
@@ -27229,7 +27229,7 @@ dwarf2out_var_location (rtx_insn *loc_note)
{
char loclabel[MAX_ARTIFICIAL_LABEL_BYTES + 2];
struct var_loc_node *newloc;
- rtx_insn *next_real, *next_note;
+ rtx_insn *next_real;
rtx_insn *call_insn = NULL;
static const char *last_label;
static const char *last_postcall_label;
@@ -27254,7 +27254,6 @@ dwarf2out_var_location (rtx_insn *loc_note)
var_loc_p = false;
next_real = dwarf2out_next_real_insn (call_insn);
- next_note = NULL;
cached_next_real_insn = NULL;
goto create_label;
}
@@ -27282,7 +27281,6 @@ dwarf2out_var_location (rtx_insn *loc_note)
var_loc_p = false;
next_real = dwarf2out_next_real_insn (call_insn);
- next_note = NULL;
cached_next_real_insn = NULL;
goto create_label;
}
@@ -27311,22 +27309,28 @@ dwarf2out_var_location (rtx_insn *loc_note)
next_real = NULL;
}
- next_note = NEXT_INSN (loc_note);
- if (! next_note
- || next_note->deleted ()
- || ! NOTE_P (next_note)
- || (NOTE_KIND (next_note) != NOTE_INSN_VAR_LOCATION
- && NOTE_KIND (next_note) != NOTE_INSN_BEGIN_STMT
- && NOTE_KIND (next_note) != NOTE_INSN_INLINE_ENTRY))
- next_note = NULL;
-
if (! next_real)
next_real = dwarf2out_next_real_insn (loc_note);
- if (next_note)
+ if (next_real)
{
- expected_next_loc_note = next_note;
- cached_next_real_insn = next_real;
+ rtx_insn *next_note = NEXT_INSN (loc_note);
+ while (next_note != next_real)
+ {
+ if (! next_note->deleted ()
+ && NOTE_P (next_note)
+ && NOTE_KIND (next_note) == NOTE_INSN_VAR_LOCATION)
+ break;
+ next_note = NEXT_INSN (next_note);
+ }
+
+ if (next_note == next_real)
+ cached_next_real_insn = NULL;
+ else
+ {
+ expected_next_loc_note = next_note;
+ cached_next_real_insn = next_real;
+ }
}
else
cached_next_real_insn = NULL;
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