Optimize new DateTime(const, const, const)

[EgorBo]

This PR optimizes new DateTime(const, const, const) case, e.g.:

[Benchmark]
public DateTime ConstDate() => new (2022, 12, 10);

Currently emits:

; Method Test:ConstDate():System.DateTime:this
G_M10442_IG01:              ;; offset=0000H
       4883EC28             sub      rsp, 40
G_M10442_IG02:              ;; offset=0004H
       48B9104AD1CEF87F0000 mov      rcx, 0x7FF8CED14A10
       BAF9000000           mov      edx, 249
       E808639F5F           call     CORINFO_HELP_GETSHARED_NONGCSTATIC_BASE
       48B8201280B98B020000 mov      rax, 0x28BB9801220
       488B00               mov      rax, gword ptr [rax]
       8B5008               mov      edx, dword ptr [rax+8]
       83FA0C               cmp      edx, 12
       762B                 jbe      SHORT G_M10442_IG05
       8B5040               mov      edx, dword ptr [rax+64]
       8B403C               mov      eax, dword ptr [rax+60]
       2BD0                 sub      edx, eax
       83FA0A               cmp      edx, 10
       7218                 jb       SHORT G_M10442_IG04
       0574430B00           add      eax, 0xB4374
       48BA00C0692AC9000000 mov      rdx, 0xC92A69C000
       480FAFC2             imul     rax, rdx
G_M10442_IG03:              ;; offset=004DH
       4883C428             add      rsp, 40
       C3                   ret      
G_M10442_IG04:              ;; offset=0052H
       E8B183FFFF           call     System.ThrowHelper:ThrowArgumentOutOfRange_BadYearMonthDay()
       CC                   int3     
G_M10442_IG05:              ;; offset=0058H
       E803AD685F           call     CORINFO_HELP_RNGCHKFAIL
       CC                   int3     
; Total bytes of code: 94

New codegen:

; Method Test:ConstDate():System.DateTime:this
G_M10442_IG01:              ;; offset=0000H
G_M10442_IG02:              ;; offset=0000H
       48B80040044BBAE2D908 mov      rax, 0x8D9E2BA4B044000
G_M10442_IG03:              ;; offset=000AH
       C3                   ret      
; Total bytes of code: 11

Benchmarks

Method	Toolchain	y	d	m	Mean
ConstDate	\Core_Root_base\corerun.exe	?	?	?	0.4368 ns
ConstDate	\Core_Root\corerun.exe	?	?	?	0.0266 ns
ConstMonth	\Core_Root_base\corerun.exe	2022	1	?	1.2839 ns
ConstMonth	\Core_Root\corerun.exe	2022	1	?	0.7184 ns
VarDate	\Core_Root_base\corerun.exe	2022	1	2	1.6864 ns
VarDate	\Core_Root\corerun.exe	2022	1	2	1.6519 ns

Feel free to reject it 🙂, eventually we should be able to get constant case codegen even with the current code, for that we need:

1. Wait till C# gets ReadOnlySpan<any primitive> for RVA data
2. Make s_daysToMonth365 and s_daysToMonth366 ReadOnlySpan<uint>
3. Implement RVA[const index] folding in JIT - unfortunately it's a bit tricky but should be doable
4. Forward Substitution (probably a bit more advanced than what Andy's currently doing)

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Issue Details

---

This PR optimizes new DateTime(const, const, const) case, e.g.:

[Benchmark]
public DateTime ConstDate() => new (2022, 12, 10);

Currently emits:

; Method Test:ConstDate():System.DateTime:this
G_M10442_IG01:              ;; offset=0000H
       4883EC28             sub      rsp, 40
G_M10442_IG02:              ;; offset=0004H
       48B9104AD1CEF87F0000 mov      rcx, 0x7FF8CED14A10
       BAF9000000           mov      edx, 249
       E808639F5F           call     CORINFO_HELP_GETSHARED_NONGCSTATIC_BASE
       48B8201280B98B020000 mov      rax, 0x28BB9801220
       488B00               mov      rax, gword ptr [rax]
       8B5008               mov      edx, dword ptr [rax+8]
       83FA0C               cmp      edx, 12
       762B                 jbe      SHORT G_M10442_IG05
       8B5040               mov      edx, dword ptr [rax+64]
       8B403C               mov      eax, dword ptr [rax+60]
       2BD0                 sub      edx, eax
       83FA0A               cmp      edx, 10
       7218                 jb       SHORT G_M10442_IG04
       0574430B00           add      eax, 0xB4374
       48BA00C0692AC9000000 mov      rdx, 0xC92A69C000
       480FAFC2             imul     rax, rdx
G_M10442_IG03:              ;; offset=004DH
       4883C428             add      rsp, 40
       C3                   ret      
G_M10442_IG04:              ;; offset=0052H
       E8B183FFFF           call     System.ThrowHelper:ThrowArgumentOutOfRange_BadYearMonthDay()
       CC                   int3     
G_M10442_IG05:              ;; offset=0058H
       E803AD685F           call     CORINFO_HELP_RNGCHKFAIL
       CC                   int3     
; Total bytes of code: 94

New codegen:

; Method Test:ConstDate():System.DateTime:this
G_M10442_IG01:              ;; offset=0000H
G_M10442_IG02:              ;; offset=0000H
       48B80040044BBAE2D908 mov      rax, 0x8D9E2BA4B044000
G_M10442_IG03:              ;; offset=000AH
       C3                   ret      
; Total bytes of code: 11

Benchmarks

Method	Toolchain	y	d	m	Mean
ConstDate	\Core_Root_base\corerun.exe	?	?	?	0.4368 ns
ConstDate	\Core_Root\corerun.exe	?	?	?	0.0266 ns
ConstMonth	\Core_Root_base\corerun.exe	2022	1	?	1.2839 ns
ConstMonth	\Core_Root\corerun.exe	2022	1	?	0.7184 ns
VarDate	\Core_Root_base\corerun.exe	2022	1	2	1.6864 ns
VarDate	\Core_Root\corerun.exe	2022	1	2	1.6519 ns

Feel free to reject it 🙂, eventually we should be able to get constant case codegen even with the current code, for that we need:

1. Wait till C# gets ReadOnlySpan<any primitive> for RVA data
2. Make s_daysToMonth365 and s_daysToMonth366 ReadOnlySpan<uint>
3. Implement RVA[const index] folding in JIT - unfortunately it's a bit tricky but should be doable
4. Forward Substitution (probably a bit more advanced than what Andy's currently doing)

Author:	EgorBo
Assignees:	-
Labels:	area-CodeGen-coreclr
Milestone:	-

[EgorBo]

Closing as it's unlikely the hack worth it or people use this pattern on hot paths, but it should be a good challenge for jit to do everything under the hood.

Another note that my single line change in morph.cpp seems to trigger some diffs: Total bytes of delta: -1496 (-0.00 % of base)