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std.simd: suggest more sensible vector sizes across the board

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Alex Rønne Petersen 2025-09-18 16:38:57 +02:00
parent 19943f0f21
commit 47c932f896
1 changed files with 18 additions and 14 deletions
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32
lib/std/simd.zig
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@ -23,20 +23,24 @@ pub fn suggestVectorLengthForCpu(comptime T: type, comptime cpu: std.Target.Cpu)
} else if (cpu.arch.isArm()) {
if (cpu.has(.arm, .neon)) break :blk 128;
} else if (cpu.arch.isAARCH64()) {
// SVE allows up to 2048 bits in the specification, as of 2022 the most powerful machine has implemented 512-bit
// I think is safer to just be on 128 until is more common
// TODO: Check on this return when bigger values are more common
if (cpu.has(.aarch64, .sve)) break :blk 128;
// NVIDIA Grace supports 128-bit SVE
// AWS Graviton3 supports 256-bit SVE
// Fujitsu A64FX supports 512-bit SVE
// -> 256-bit seems like a good default for now.
if (cpu.has(.aarch64, .sve)) break :blk 256;
if (cpu.has(.aarch64, .neon)) break :blk 128;
} else if (cpu.arch.isPowerPC()) {
if (cpu.has(.powerpc, .altivec)) break :blk 128;
} else if (cpu.arch == .hexagon) {
if (cpu.has(.hexagon, .hvx_length64b)) break :blk 512;
if (cpu.has(.hexagon, .hvx)) break :blk 1024;
} else if (cpu.arch.isLoongArch()) {
if (cpu.has(.loongarch, .lasx)) break :blk 256;
if (cpu.has(.loongarch, .lsx)) break :blk 128;
} else if (cpu.arch.isMIPS()) {
if (cpu.has(.mips, .msa)) break :blk 128;
// TODO: Test MIPS capability to handle bigger vectors
// In theory MDMX and by extension mips3d have 32 registers of 64 bits which can use in parallel
// for multiple processing, but I don't know what's optimal here, if using
// the 2048 bits or using just 64 per vector or something in between
if (cpu.has(.mips, .mips3d)) break :blk 64;
} else if (cpu.arch.isPowerPC()) {
if (cpu.has(.powerpc, .vsx)) break :blk 128;
if (cpu.has(.powerpc, .altivec)) break :blk 128;
} else if (cpu.arch.isRISCV()) {
// In RISC-V Vector Registers are length agnostic so there's no good way to determine the best size.
// The usual vector length in most RISC-V cpus is 256 bits, however it can get to multiple kB.
@ -60,12 +64,12 @@ pub fn suggestVectorLengthForCpu(comptime T: type, comptime cpu: std.Target.Cpu)
break :blk 256;
}
} else if (cpu.arch == .s390x) {
if (cpu.has(.s390x, .vector)) break :blk 128;
} else if (cpu.arch.isSPARC()) {
// TODO: Test Sparc capability to handle bigger vectors
// In theory Sparc have 32 registers of 64 bits which can use in parallel
// for multiple processing, but I don't know what's optimal here, if using
// the 2048 bits or using just 64 per vector or something in between
if (cpu.hasAny(.sparc, &.{ .vis, .vis2, .vis3 })) break :blk 64;
} else if (cpu.arch == .ve) {
if (cpu.has(.ve, .vpu)) break :blk 2048;
} else if (cpu.arch.isWasm()) {
if (cpu.has(.wasm, .simd128)) break :blk 128;
}