JIT: Optimize Memmove unrolling for constant src #108576
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Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch |
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/azp run runtime-coreclr outerloop, runtime-coreclr jitstress, runtime-coreclr pgo |
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Co-authored-by: Jakob Botsch Nielsen <[email protected]>
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@MihuBot -arm64 |
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@EgorBo Regressions on arm64?
EgorBot/runtime-utils#110 (comment)
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load might be faster than up to 4 instructions to compose a 64bit constant for "FALS" or "TRUE" utf16 strings on arm64, but it's tricky in the real world, the load might be under contention. Anyway, we'll see once dotnet/performance run finishes |
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LowerCallMemmovealready does a good job unrolling Memmove. Unfortunately, it leaves some opportunities on the table when the source can be a constant (esp, GPR constant), so we can skip a memory load. The reason is thatLowerCallMemmovecannot rely on VN for that as it's too late.Codegen diff:
; Method Benchmarks:Test_utf16(System.Span`1[ushort]):this (FullOpts) sub rsp, 40 mov rax, bword ptr [rdx] mov ecx, dword ptr [rdx+0x08] cmp ecx, 4 jl SHORT G_M39687_IG04 - mov rcx, 0x21A00204FFC - mov rdx, qword ptr [rcx] - mov qword ptr [rax], rdx + mov rcx, 0x65007500720054 + mov qword ptr [rax], rcx add rsp, 40 ret G_M39687_IG04: call [System.ThrowHelper:ThrowArgumentException_DestinationTooShort()] int3 -; Total bytes of code: 43 +; Total bytes of code: 40 ; Method Benchmarks:Test_utf8(System.Span`1[ubyte]):this (FullOpts) sub rsp, 40 mov rax, bword ptr [rdx] mov ecx, dword ptr [rdx+0x08] cmp ecx, 4 jl SHORT G_M38560_IG04 - mov rcx, 0x2C391CC5380 ; static handle - mov edx, dword ptr [rcx] - mov dword ptr [rax], edx + mov dword ptr [rax], 0x65757254 add rsp, 40 ret G_M38560_IG04: call [System.ThrowHelper:ThrowArgumentException_DestinationTooShort()] int3 -; Total bytes of code: 41 +; Total bytes of code: 33Diffs