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Title: Performance improvements
Author: rodarima
Created: Sun, 13 Apr 2025 16:52:07 +0000
State: open

Rendering https://html.spec.whatwg.org/ several times (via refresh) leads to the following perf trace on armv7:

```
# To display the perf.data header info, please use --header/--header-only options.
#
#
# Total Lost Samples: 0
#
# Samples: 169K of event 'cycles:Pu'
# Event count (approx.): 33718562150
#
# Overhead  Command  Shared Object            Symbol
# ........  .......  .......................  ................................................................................................................................................
#
     7.03%  dillo    dillo                    [.] lout::misc::NotSoSimpleVector<dw::Textblock::Word>::getRef(int) const
     6.34%  dillo    ld-musl-armhf.so.1       [.] __strchrnul
     2.69%  dillo    dillo                    [.] Html_write_raw(DilloHtml*, char*, int, int)
     2.22%  dillo    ld-musl-armhf.so.1       [.] __libc_malloc_impl
     1.91%  dillo    ld-musl-armhf.so.1       [.] strncmp
     1.86%  dillo    dillo                    [.] lout::misc::NotSoSimpleVector<dw::Textblock::Word>::size() const
     1.78%  dillo    dillo                    [.] dw::Textblock::accumulateWordData(int)
     1.64%  dillo    libz.so.1.3.1            [.] crc32_z
     1.51%  dillo    ld-musl-armhf.so.1       [.] get_meta
     1.45%  dillo    dillo                    [.] CssStyleSheet::apply(CssPropertyList*, Doctree*, DoctreeNode const*, MatchCache*) const
     1.37%  dillo    dillo                    [.] int lout::misc::max<int>(int, int)
     1.29%  dillo    dillo                    [.] dw::Textblock::BadnessAndPenalty::penaltyValue(int, int)
     1.29%  dillo    ld-musl-armhf.so.1       [.] strcspn
     1.22%  dillo    ld-musl-armhf.so.1       [.] __libc_free
     1.20%  dillo    dillo                    [.] dw::Textblock::BadnessAndPenalty::badnessValue(int)
     1.17%  dillo    dillo                    [.] lout::identity::IdentifiableObject::instanceOf(int)
     1.16%  dillo    dillo                    [.] dw::Textblock::addText(char const*, unsigned int, dw::core::style::Style*)
     1.16%  dillo    dillo                    [.] dw::Textblock::wrapWordInFlow(int, bool)
     1.09%  dillo    dillo                    [.] a_Html_get_attr(DilloHtml*, char const*, int, char const*)
     1.03%  dillo    dillo                    [.] dw::Textblock::getWidgetRegardingBorderForLine(int, int)
     1.00%  dillo    dillo                    [.] CssSelector::match(Doctree*, DoctreeNode const*, int, CssSelector::Combinator, MatchCache*)
     0.92%  dillo    ld-musl-armhf.so.1       [.] cached_aligned32
     0.89%  dillo    dillo                    [.] dw::Textblock::getLineStretchability(int)
     0.86%  dillo    ld-musl-armhf.so.1       [.] strlen
     0.85%  dillo    dillo                    [.] dw::core::Widget::getStyle()
     0.85%  dillo    dillo                    [.] dw::Textblock::calcBorders(int, int)
     0.83%  dillo    dillo                    [.] dw::Textblock::handleWordExtremes(int)
     0.80%  dillo    ld-musl-armhf.so.1       [.] alloc_slot
     0.79%  dillo    dillo                    [.] dw::Textblock::BadnessAndPenalty::compareTo(int, dw::Textblock::BadnessAndPenalty*)
     0.78%  dillo    dillo                    [.] lout::misc::SimpleVector<dw::Textblock::Line>::size() const
     0.77%  dillo    dillo                    [.] lout::container::untyped::Vector::get(int) const
     0.77%  dillo    dillo                    [.] lout::object::ConstString::hashValue(char const*)
     0.66%  dillo    libgcc_s.so.1            [.] __aeabi_idiv
     0.66%  dillo    dillo                    [.] CssSimpleSelector::match(DoctreeNode const*)
     0.64%  dillo    dillo                    [.] lout::container::untyped::HashSet::findNode(lout::object::Object*) const
     0.63%  dillo    dillo                    [.] lout::misc::SimpleVector<dw::Textblock::Line>::getRef(int) const
```

There is a bottleneck in getRef of the NotSoSimpleVector. We could probably optimize the hot path as it is doing several checks that are not really needed. Including two asserts.

```
       │     0005f7fc <lout::misc::NotSoSimpleVector<dw::Textblock::Word>::getRef(int) const>:                                                                                                                                                                                                                                                                                                                                                                                             ▒
       │     /**                                                                                                                                                                                                                                                                                                                                                                                                                                                                           ▒
       │     * \brief Return the reference of one element.                                                                                                                                                                                                                                                                                                                                                                                                                                 ▒
       │     *                                                                                                                                                                                                                                                                                                                                                                                                                                                                             ▒
       │     * \sa misc::SimpleVector::get                                                                                                                                                                                                                                                                                                                                                                                                                                                 ▒
       │     */                                                                                                                                                                                                                                                                                                                                                                                                                                                                            ▒
       │     inline T* getRef (int i) const                                                                                                                                                                                                                                                                                                                                                                                                                                                ▒
  2.72 │       push  {r7, lr}                                                                                                                                                                                                                                                                                                                                                                                                                                                              ▒
  1.83 │       sub   sp, #8                                                                                                                                                                                                                                                                                                                                                                                                                                                                ▒
  2.42 │       add   r7, sp, #0                                                                                                                                                                                                                                                                                                                                                                                                                                                            ▒
  5.87 │       str   r0, [r7, #4]                                                                                                                                                                                                                                                                                                                                                                                                                                                          ▒
  1.99 │       str   r1, [r7, #0]                                                                                                                                                                                                                                                                                                                                                                                                                                                          ▒
       │     {                                                                                                                                                                                                                                                                                                                                                                                                                                                                             ▒
       │     if (this->startExtra == -1) {                                                                                                                                                                                                                                                                                                                                                                                                                                                 ▒
  2.01 │       ldr   r3, [r7, #4]                                                                                                                                                                                                                                                                                                                                                                                                                                                          ▒
  5.73 │       ldr   r3, [r3, #28]                                                                                                                                                                                                                                                                                                                                                                                                                                                         ▒
  3.61 │       cmp.w r3, #4294967295                                                                                                                                                                                                                                                                                                                                                                                                                                                       ▒
       │       bne.n 5f84e <lout::misc::NotSoSimpleVector<dw::Textblock::Word>::getRef(int) const+0x52>                                                                                                                                                                                                                                                                                                                                                                                    ▒
       │     assert (i >= 0 && i < this->numMain);                                                                                                                                                                                                                                                                                                                                                                                                                                         ▒
  5.79 │       ldr   r3, [r7, #0]                                                                                                                                                                                                                                                                                                                                                                                                                                                          ▒
  3.48 │       cmp   r3, #0                                                                                                                                                                                                                                                                                                                                                                                                                                                                ▒
  0.34 │       blt.n 5f820 <lout::misc::NotSoSimpleVector<dw::Textblock::Word>::getRef(int) const+0x24>                                                                                                                                                                                                                                                                                                                                                                                    ▒
  5.49 │       ldr   r3, [r7, #4]                                                                                                                                                                                                                                                                                                                                                                                                                                                          ▒
  5.47 │       ldr   r3, [r3, #12]                                                                                                                                                                                                                                                                                                                                                                                                                                                         ▒
  1.67 │       ldr   r2, [r7, #0]                                                                                                                                                                                                                                                                                                                                                                                                                                                          ▒
  3.40 │       cmp   r2, r3                                                                                                                                                                                                                                                                                                                                                                                                                                                                ▒
       │       blt.n 5f834 <lout::misc::NotSoSimpleVector<dw::Textblock::Word>::getRef(int) const+0x38>                                                                                                                                                                                                                                                                                                                                                                                    ▒
       │       ldr   r3, [pc, #228]  @ (5f908 <lout::misc::NotSoSimpleVector<dw::Textblock::Word>::getRef(int) const+0x10c>)                                                                                                                                                                                                                                                                                                                                                               ▒
       │       add   r3, pc                                                                                                                                                                                                                                                                                                                                                                                                                                                                ▒
       │       movw  r2, #479        @ 0x1df                                                                                                                                                                                                                                                                                                                                                                                                                                               ▒
       │       ldr   r1, [pc, #224]  @ (5f90c <lout::misc::NotSoSimpleVector<dw::Textblock::Word>::getRef(int) const+0x110>)                                                                                                                                                                                                                                                                                                                                                               ▒
       │       add   r1, pc                                                                                                                                                                                                                                                                                                                                                                                                                                                                ▒
       │       ldr   r0, [pc, #224]  @ (5f910 <lout::misc::NotSoSimpleVector<dw::Textblock::Word>::getRef(int) const+0x114>)                                                                                                                                                                                                                                                                                                                                                               ▒
       │       add   r0, pc                                                                                                                                                                                                                                                                                                                                                                                                                                                                ▒
       │     → blx   strrchr@plt                                                                                                                                                                                                                                                                                                                                                                                                                                                           ▒
       │     return this->arrayMain + i;                                                                                                                                                                                                                                                                                                                                                                                                                                                   ▒
  5.98 │       ldr   r3, [r7, #4]                                                                                                                                                                                                                                                                                                                                                                                                                                                          ▒
  5.65 │       ldr   r1, [r3, #0]                                                                                                                                                                                                                                                                                                                                                                                                                                                          ▒
  1.80 │       ldr   r2, [r7, #0]                                                                                                                                                                                                                                                                                                                                                                                                                                                          ▒
  3.96 │       mov   r3, r2                                                                                                                                                                                                                                                                                                                                                                                                                                                                ▒
  4.10 │       lsls  r3, r3, #1                                                                                                                                                                                                                                                                                                                                                                                                                                                            ▒
  1.86 │       add   r3, r2                                                                                                                                                                                                                                                                                                                                                                                                                                                                ▒
  3.54 │       lsls  r2, r3, #3                                                                                                                                                                                                                                                                                                                                                                                                                                                            ▒
  1.68 │       subs  r2, r2, r3                                                                                                                                                                                                                                                                                                                                                                                                                                                            ▒
  3.85 │       lsls  r3, r2, #2                                                                                                                                                                                                                                                                                                                                                                                                                                                            ▒
  2.06 │       mov   r2, r3                                                                                                                                                                                                                                                                                                                                                                                                                                                                ▒
  1.84 │       mov   r3, r2                                                                                                                                                                                                                                                                                                                                                                                                                                                                ▒
  2.02 │       add   r3, r1                                                                                                                                                                                                                                                                                                                                                                                                                                                                ▒
       │       b.n   5f8fe <lout::misc::NotSoSimpleVector<dw::Textblock::Word>::getRef(int) const+0x102>                                                                                                                                                                                                                                                                                                                                                                                   ▒
       │     } else {                                                                                                                                                                                                                                                                                                                                                                                                                                                                      ▒
       │     if (i < this->startExtra) {                                                                                                                                                                                                                                                                                                                                                                                                                                                   ▒
       │       ldr   r3, [r7, #4]                                                                                                                                                                                                                                                                                                                                                                                                                                                          ▒
       │       ldr   r3, [r3, #28]                                                                                                                                                                                                                                                                                                                                                                                                                                                         ▒
       │       ldr   r2, [r7, #0]                                                                                                                                                                                                                                                                                                                                                                                                                                                          ▒
       │       cmp   r2, r3                                                                                                                                                                                                                                                                                                                                                                                                                                                                ▒
       │       bge.n 5f88c <lout::misc::NotSoSimpleVector<dw::Textblock::Word>::getRef(int) const+0x90>                                                                                                                                                                                                                                                                                                                                                                                    ▒
       │     assert (i >= 0);                                                                                                                                                                                                                                                                                                                                                                                                                                                              ▒
       │       ldr   r3, [r7, #0]                                                                                                                                                                                                                                                                                                                                                                                                                                                          ▒
       │       cmp   r3, #0                                                                                                                                                                                                                                                                                                                                                                                                                                                                ▒
       │       bge.n 5f872 <lout::misc::NotSoSimpleVector<dw::Textblock::Word>::getRef(int) const+0x76>                                                                                                                                                                                                                                                                                                                                                                                    ▒
       │       ldr   r3, [pc, #180]  @ (5f914 <lout::misc::NotSoSimpleVector<dw::Textblock::Word>::getRef(int) const+0x118>)                                                                                                                                                                                                                                                                                                                                                               ▒
       │       add   r3, pc                                                                                                                                                                                                                                                                                                                                                                                                                                                                ▒
       │       movw  r2, #483        @ 0x1e3                                                                                                                                                                                                                                                                                                                                                                                                                                               ▒
       │       ldr   r1, [pc, #176]  @ (5f918 <lout::misc::NotSoSimpleVector<dw::Textblock::Word>::getRef(int) const+0x11c>)                                                                                                                                                                                                                                                                                                                                                               ▒
       │       add   r1, pc                                                                                                                                                                                                                                                                                                                                                                                                                                                                ▒
       │       ldr   r0, [pc, #176]  @ (5f91c <lout::misc::NotSoSimpleVector<dw::Textblock::Word>::getRef(int) const+0x120>)                                                                                                                                                                                                                                                                                                                                                               ▒
       │       add   r0, pc                                                                                                                                                                                                                                                                                                                                                                                                                                                                ▒
       │     → blx   strrchr@plt 
...
```