2009158 - [riscv64] Use Zba and Zbb extensions more in [Macro]Assembler-riscv64

Status: NEW

(Core :: JavaScript Engine: JIT, task)

Description

[Rong Bao [:csmantle]]

Inspired by [^1] and [^2] (Chinese), we may be able to fuse more instructions using Zba and Zbb instructions, thanks to the foundation laid by Bug 2003218.

Comment 1

[Rong Bao [:csmantle]]

Attachment: WIP: Bug 2009158 - [riscv64] Part 1: Move {Sign,Zero}Extend{Byte,Short,Word} into Assembler-riscv64.h for broader usage. r=jandem

Comment 2

[Rong Bao [:csmantle]]

Attachment: WIP: Bug 2009158 - [riscv64] Part 2: Use ZeroExtendWord in Assembler::GeneralLi. r=jandem

Comment 3

[Rong Bao [:csmantle]]

Attachment: WIP: Bug 2009158 - [riscv64] Part 3: Use shXadd[.uw] in MacroAssemblerRiscv64::computeScaledAddress[32]. r=jandem

Comment 4

[Rong Bao [:csmantle]]

Attachment: WIP: Bug 2009158 - [riscv64] Part 4: Use clz in MacroAssemblerRiscv64::Clz64. r=jandem

Comment 5

[Rong Bao [:csmantle]]

Attachment: WIP: Bug 2009158 - [riscv64] Part 5: Use rol[w] in MacroAssemblerRiscv64::[D]Rol. r=jandem

Comment 6

[Rong Bao [:csmantle]]

Attachment: WIP: Bug 2009158 - [riscv64] Part 6: Use {max,min} in MacroAssemblerRiscv64Compat::minMaxPtr. r=jandem

Comment 7

[Rong Bao [:csmantle]]

Hi Jan, when reading the implementation of minMaxPtr [^1], I find it interesting that it uses signed comparisons (Assembler::GreaterThanOrEqual and Assembler::LessThanOrEqual). I guess there are some special considerations behind this, as other architectures also use signed comparisons, but I haven't figured it out yet. Would you mind providing me with some pointers on this?

Comment 8

[Jan de Mooij [:jandem]]

(In reply to Rong Bao [:csmantle] from comment #7)

Hi Jan, when reading the implementation of minMaxPtr [^1], I find it interesting that it uses signed comparisons (Assembler::GreaterThanOrEqual and Assembler::LessThanOrEqual). I guess there are some special considerations behind this, as other architectures also use signed comparisons, but I haven't figured it out yet. Would you mind providing me with some pointers on this?

Initially we had the Int32 version (minMax32) where we need signed comparisons because this is used for the result of Math.min and Math.max. Unsigned comparisons would give us the wrong results.

minMaxPtr is used for the MIRType::IntPtr version and I think we similarly want the signed version for things like this.

Comment 9

[Rong Bao [:csmantle]]

Thanks.

I'm collecting perf numbers of before and after this stack, but preliminarily it doesn't show much observable improvements. Will look into the cause of this.