| Issue |
110317
|
| Summary |
[AVX2+] Vectorized `1 << u4` in a byte vector should turn into `vpshufb`
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
Validark
|
This code: ([Godbolt link](https://zig.godbolt.org/#g:!((g:!((g:!((h:codeEditor,i:(filename:'1',fontScale:14,fontUsePx:'0',j:3,lang:zig,selection:(endColumn:2,endLineNumber:3,positionColumn:2,positionLineNumber:3,selectionStartColumn:2,selectionStartLineNumber:3,startColumn:2,startLineNumber:3),source:'export+fn+foo(chunk:+@Vector(32,+u8))+@TypeOf(chunk)+%7B%0A++++return+@as(@TypeOf(chunk),+@splat(1))+%3C%3C+@truncate(chunk+%3E%3E+@splat(4))%3B%0A%7D'),l:'5',n:'1',o:'Zig+source+%233',t:'0')),header:(),k:50.61449749453956,l:'4',m:100,n:'0',o:'',s:0,t:'0'),(g:!((h:compiler,i:(compiler:ztrunk,filters:(b:'0',binary:'1',binaryObject:'1',commentOnly:'0',debugCalls:'1',demangle:'0',directives:'0',execute:'1',intel:'0',libraryCode:'0',trim:'1',verboseDemangling:'0'),flagsViewOpen:'1',fontScale:14,fontUsePx:'0',j:1,lang:zig,libs:!(),options:'-O+ReleaseFast+-target+x86_64-linux+-mcpu%3Dznver3',overrides:!(),selection:(endColumn:33,endLineNumber:18,positionColumn:33,positionLineNumber:18,selectionStartColumn:33,selectionStartLineNumber:18,startColumn:33,startLineNumber:18),source:3),l:'5',n:'0',o:'+zig+trunk+(Editor+%233)',t:'0')),header:(),k:49.38550250546045,l:'4',m:100,n:'0',o:'',s:0,t:'0')),l:'2',n:'0',o:'',t:'0')),version:4))
```zig
export fn foo(chunk: @Vector(32, u8)) @TypeOf(chunk) {
return @as(@TypeOf(chunk), @splat(1)) << @truncate(chunk >> @splat(4));
}
```
```llvm
define dso_local range(i8 1, -127) <32 x i8> @foo(<32 x i8> %0) local_unnamed_addr {
Entry:
%1 = lshr <32 x i8> %0, <i8 4, i8 4, i8 4, i8 4, i8 4, i8 4, i8 4, i8 4, i8 4, i8 4, i8 4, i8 4, i8 4, i8 4, i8 4, i8 4, i8 4, i8 4, i8 4, i8 4, i8 4, i8 4, i8 4, i8 4, i8 4, i8 4, i8 4, i8 4, i8 4, i8 4, i8 4, i8 4>
%2 = and <32 x i8> %1, <i8 7, i8 7, i8 7, i8 7, i8 7, i8 7, i8 7, i8 7, i8 7, i8 7, i8 7, i8 7, i8 7, i8 7, i8 7, i8 7, i8 7, i8 7, i8 7, i8 7, i8 7, i8 7, i8 7, i8 7, i8 7, i8 7, i8 7, i8 7, i8 7, i8 7, i8 7, i8 7>
%3 = shl nuw <32 x i8> <i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1, i8 1>, %2
ret <32 x i8> %3
}
```
Compiles like so for Zen 3:
```asm
.LCPI0_1:
.zero 32,16
.LCPI0_2:
.zero 32,252
.LCPI0_3:
.zero 32,224
.LCPI0_4:
.byte 1
foo:
vpsllw ymm0, ymm0, 1
vpbroadcastb ymm1, byte ptr [rip + .LCPI0_4]
vpblendvb ymm1, ymm1, ymmword ptr [rip + .LCPI0_1], ymm0
vpand ymm0, ymm0, ymmword ptr [rip + .LCPI0_3]
vpsllw ymm2, ymm1, 2
vpand ymm2, ymm2, ymmword ptr [rip + .LCPI0_2]
vpaddb ymm0, ymm0, ymm0
vpblendvb ymm1, ymm1, ymm2, ymm0
vpaddb ymm0, ymm0, ymm0
vpaddb ymm2, ymm1, ymm1
vpblendvb ymm0, ymm1, ymm2, ymm0
ret
```
However, because the bytes resulting from `chunk >> @splat(4)` are in the range [0, 15], we can precompute all 16 possible answers and use vpshufb instead ([Godbolt, full code](https://zig.godbolt.org/#z:OYLghAFBqd5QCxAYwPYBMCmBRdBLAF1QCcAaPECAMzwBtMA7AQwFtMQByARg9KtQYEAysib0QXACx8BBAKoBnTAAUAHpwAMvAFYgAzKVpMGoAF55gpJfWQE8Ayo3QBhVLQCuLBiABMpJwAyeAyYAHKeAEaYxPoAbKQADqgKhPYMrh5eEonJqQJBIeEsUTEAHFaYNnYCQgRMxAQZnt5%2B1pi2abX1BAVhkdFxVnUNTVlcQ929RSUgpQCUVqjuxMjsHGgMCgQA1Fvo2wCkegAi2wACeCxJDRAHPj57dz5zRwBCBxoAghtb2xHudDsDEOJ3Ol2uBFu93%2BgOCTxeeneXw%2BnyowP4qAgyAQ7gYAGsQOcAGrtIjECB6PzbdzzObnAAqAE8EpgAPJULE4/F0g4AdiRn22Qu2xEwBGWwLOTAUEDOTJZ7M5uLxC3OCgSRkhXDmPL0ziOznOBGIuNEBEwSvxIOwR2wao1TEhkh1bxRfOObq%2BmFUEO2aL9qFQPktBOJpJIFKpNJ1DOZbI52OVPP5KOF2x%2BOzqEXoINOaCudjYAcxewAdCkWOhS6KWY7ZSlTPHZfKm4nuaqyxWq/Y6hAaaRtlxYrr9Xr7ZqIM6XYjU8LReLiMCAG4JBQ4qgRCBZ%2BgDtt46228d1qeu5G8j3Ir7%2Bldr9wbrdMbPsbbGRkEOMD4L4VYKQlyuOKtumAxv%2BCockByYCmmeBUNssrBK4BaXBaMZ8lBabCku9QipgCjuLQBB/i2ipfngP66qcuJYDQIToKegoYUK/DEHBGilqWZwRIQQh4I2iqgU2pHkXSAD02zzIcvLOHgfKGmhs6MWmGbbF%2B3q5ipDDfrhBwAKyvDJOkejOXyKRhop4QRun6bppxHKcMFwapqgHqCGiqKUGh0ho2yVEo2xAVZTmHD4OlwZx3G8U2AmAY%2B9AxmJ8w2fRpnup6DGMfOEo4RZBDJcKqWXul6YCL8bAEAgGAKOpWwmrYknoYx3rmoufqSk8tC0EuLClu5sSlkwS6qDpXA%2BKWq7rqWESlsNPhPLKJK2BGsTSNS8wDmcC1khAy0DtGdIbeG5I7atCINRhTXROibX3B1XU9aUfUDaoo3jXek1zQdi3kpSu1rWGX2Rr9IGbRGP0nXljWqM1V3nO1nXdb15YKEoehjbeVCTaWI2lB9IPkkOQPrXjEAEyd%2B3E6T0YQ5JRkCgpOELsCCgAO6ENiYXEeBsXAZB9Npp9W3HdGuaHg5WKoEhRZlvS9TAGK919VQmCOssmBCGKAAS0oQDCBHBKWyAJO4pZKyr5kDv1g0zREzMxmVFXoAoHFw3diNPTNaMTVNM1zUBn6aWRuF0r5mDnPmCR0DgxDEBGTzOMocj%2BbLYrbEYyB4lVeEJL6zHbDe64RD79wLHzwoC6DUYSXZouweLkuh9LycEArJvKwuaua9rutAgbRut2buEW09zx0vblXOzd8Mt8PntvREvvc/7WkKMHtB%2BWc4eR9g0ex/c8eJ8Mcs7GnGe7O42ckDsuf53eEQhbE8KkKXQrl/j8QnSLeh2mL4eFg3BBVhlsQI%2BLdTbt3VgQLWMpu760NsbMBqsFAW2RijO2YoHZOzOC7BGD0kYo1nhjKa2MF5PiXoHFePk16hw3hLCO9Bt4x3JHHBOSdgEpxPpnc%2BOcSB51ehuYhxcn4mUUiHT%2BdoaFXC3jvckZYqAsGbr/ZCyhiDBEhE8AAkgwLCtA8D7Flp4RgmY4zbASNKJQ%2BwiC8PRhEQk8lzy6WcAwJ4Fs0LRS5k%2BF454dRCKKqlYynx3QcAWLQTgOleDeG4LwVAnAABaFhdhLBWKHO4eg9C8EIhwLQ3iEDKywDECACwCQ6TYj4XkeguAaAAJzVN5DpMpUhpAhI4JIXgLAJAaA0KQCJWhSDRI4LwX8nSMlZNIHAWASBN70DIBQOudCBimGNMqPggJoi/h1poXgXFmDEEZJwHgpAtn1EZKyCI2hSR7N4PmNgghWQMFoLszJvAsD/GAM4MQa8LmkCwCwYwwBxCPK%2BXgUUHQly4Q2f4VQ7R3Dmk%2Baoyo4KdERGIEc1wWBwXGkuJ80FxAIjJEwMcTAPyTA6JMBshYVAjDAAUESPAmBmashZBE/Z/BBAiDEOwKQMhBCKBUOoAFuhxhGFJeYSwiLfyQAWKgBI1RNicAALSsm2AAJUqMrJQAAxaUOw5WHxTr1AA%2BstOVJL3DOTlSwOBdlTBaOiGk3p2KVFYHFQUioVQ0iOE0qMbwXByiBGCH0YoAwuAGCSCkGVXqJDlFDXkBgUx%2BgxGDa60knRhiNDcM0SNSaOg1FTXGwNCaDBbG6BGn1EwGh5pmMGhYChEmrH0ME0J4TwV9O2CK/yJorQQFwIQHhKS9BzHSWShYOSmB5MoIUkAkhKmll5D4WIpRKkdI0D4SQc7Si8kMJwFppA2kVM6d0qJnABkgCGUOzdHAfBNoBX0wdjzvHYpSA4SQQA%3D)):
```zig
export fn foo2(chunk: @Vector(32, u8)) @TypeOf(chunk) {
const table = comptime foo(std.simd.repeat(@sizeOf(@TypeOf(chunk)), std.simd.iota(u8, 16) << @splat(4)));
return vpshufb(table, chunk >> @splat(4));
}
fn vpshufb(table: anytype, indices: @TypeOf(table)) @TypeOf(table) {
if (@inComptime()) {
var result: @TypeOf(indices) = undefined;
for (0..@bitSizeOf(@TypeOf(indices)) / 8) |i| {
const index = indices[i];
result[i] = if (index >= 0x80) 0 else table[index % (@bitSizeOf(@TypeOf(table)) / 8)];
}
return result;
}
const methods = struct {
extern fn @"llvm.x86.avx512.pshuf.b.512"(@Vector(64, u8), @Vector(64, u8)) @Vector(64, u8);
extern fn @"llvm.x86.avx2.pshuf.b"(@Vector(32, u8), @Vector(32, u8)) @Vector(32, u8);
extern fn @"llvm.x86.ssse3.pshuf.b.128"(@Vector(16, u8), @Vector(16, u8)) @Vector(16, u8);
};
return switch (@TypeOf(table)) {
@Vector(64, u8) => if (comptime std.Target.x86.featureSetHas(builtin.cpu.features, .avx512bw)) methods.@"llvm.x86.avx512.pshuf.b.512"(table, indices) else @compileError("CPU target lacks support for vpshufb512"),
@Vector(32, u8) => if (comptime std.Target.x86.featureSetHas(builtin.cpu.features, .avx2)) methods.@"llvm.x86.avx2.pshuf.b"(table, indices) else @compileError("CPU target lacks support for vpshufb256"),
@Vector(16, u8) => if (comptime std.Target.x86.featureSetHas(builtin.cpu.features, .ssse3)) methods.@"llvm.x86.ssse3.pshuf.b.128"(table, indices) else @compileError("CPU target lacks support for vpshufb128"),
else => @compileError(std.fmt.comptimePrint("Invalid argument type passed to vpshufb: {}\n", .{@TypeOf(table)})),
};
}
```
```asm
.LCPI0_0:
.zero 32,15
.byte 1
.byte 2
.byte 4
.byte 8
.byte 16
.byte 32
.byte 64
.byte 128
.byte 1
.byte 2
.byte 4
.byte 8
.byte 16
.byte 32
.byte 64
.byte 128
.byte 1
.byte 2
.byte 4
.byte 8
.byte 16
.byte 32
.byte 64
.byte 128
.byte 1
.byte 2
.byte 4
.byte 8
.byte 16
.byte 32
.byte 64
.byte 128
.LCPI0_2:
.byte 1
.byte 2
.byte 4
.byte 8
.byte 16
.byte 32
.byte 64
.byte 128
foo2:
vpsrlw ymm0, ymm0, 4
vpand ymm0, ymm0, ymmword ptr [rip + .LCPI0_0]
vpbroadcastq ymm1, qword ptr [rip + .LCPI0_2]
vpshufb ymm0, ymm1, ymm0
ret
```
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