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From: "dmitry.neverov at jetbrains dot com"
 <sourceware-bugzilla@sourceware.org>
To: gdb-prs@sourceware.org
Subject: [Bug mi/31324] New: -var-create: slowdown due to children printing
Date: Thu, 01 Feb 2024 12:17:56 +0000
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X-Bugzilla-Version: 14.1
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D31324

            Bug ID: 31324
           Summary: -var-create: slowdown due to children printing
           Product: gdb
           Version: 14.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: mi
          Assignee: unassigned at sourceware dot org
          Reporter: dmitry.neverov at jetbrains dot com
  Target Milestone: ---

Fix for https://sourceware.org/bugzilla/show_bug.cgi?id=3D11335
changed the logic of -var-create. Before, if a var had children,
-var-create returned "{...}" as a value. Now, it appends the
pretty printer's to_string result to the printed children.

It looks like there is no way to disable this behavior.

New logic has performance implications. For example, running

  -var-create v1 * "ss"

in the following program:

typedef struct {
  int x, y;
} SlowStruct;

int main() {
  SlowStruct ss[100] =3D {0};
  return 0; //break
}

will be slow if SlowStruct has a slow pretty-printer:

import gdb
import gdb.printing
import time

class SlowStructPrinter:
    def __init__(self, val):
        self.val =3D val

    def to_string(self):
        time.sleep(1)
        return ("slow struct")

def slowStructPrinterMatcher(val):
    if "SlowStruct" in str(val.type):
        return SlowStructPrinter(val)

gdb.pretty_printers.append(slowStructPrinterMatcher)

This was fast in 13.2, because children were not printed.

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