RFR: 8323503: x86: Shorter movptr(reg, imm) for 32-bit unsigned immediates

[Vladimir Kozlov]

On Wed, 10 Jan 2024 11:05:03 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> We noticed in [JDK-8323497](https://bugs.openjdk.org/browse/JDK-8323497) that `movptr` optimization done in [JDK-8319406](https://bugs.openjdk.org/browse/JDK-8319406) is not covering the case of immediates that fit in 32-bit unsigned, but do not fit in 32-bit signed. In that case, we can maybe do `mov r32, imm32` and rely on x86 zero-extending 32->64 bit for us. Since `movl` encoding is smaller than sign-extending `movq`, we also save more code on most paths that [JDK-8319406](https://bugs.openjdk.org/browse/JDK-8319406) improved.
> 
> There are a few interesting conversions along the way:
>   1. `intptr_t` -> `uint32_t` (this method)
>   2. `uint32_t` -> `int32_t` (argument conversion for `movl`)
>   3. `int32_t` -> `uint32_t` (in `emit_int32`)
>  
> I believe these are safe after `is_uimm32` check, but please check (sic) me on this.
> 
> Note that x86_64 matcher already does similar thing for immediates:
> 
> 
> // Long Immediate 32-bit unsigned
> operand immUL32()
> %{
>   predicate(n->get_long() == (unsigned int) (n->get_long()));
>   match(ConL);
>   ...
> %}
> 
> instruct loadConUL32(rRegL dst, immUL32 src)
> %{
>   ...
>   format %{ "movl    $dst, $src\t# long (unsigned 32-bit)" %}
>   ins_encode %{
>     __ movl($dst$$Register, $src$$constant);
>   %}
> %}
> 
> 
> Additional testing:
>  - [x] Linux x86_64 server fastdebug, `tier{1,2,3,4}`
> 
> Code sizes for `Hello World`, `-Xcomp`:
> 
> 
> # Before
>   tier1 nmethod code size         :   426208 bytes
>   tier2 nmethod code size         :   462880 bytes
>   tier3 nmethod code size         :   889992 bytes
>   tier4 nmethod code size         :  1244448 bytes
> 
> # After
>   tier1 nmethod code size         :   425768 bytes (-0.1%)
>   tier2 nmethod code size         :   462400 bytes (-0.1%)
>   tier3 nmethod code size         :   882072 bytes (-0.8%)
>   tier4 nmethod code size         :  1236448 bytes (-0.6%)

What about next?:

// src should NEVER be a real pointer. Use AddressLiteral for true pointers
void MacroAssembler::movptr(Address dst, intptr_t src, Register rscratch) {
  if (is_simm32(src)) {
    movptr(dst, checked_cast<int32_t>(src));

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PR Review: https://git.openjdk.org/jdk/pull/17343#pullrequestreview-1814156793