Consider expanding casts in late phases

[EgorBo]

void Foo(object o)
{
    for (int i = 0; i < 100; i++)
    {
        if (o is string)
            Console.WriteLine("str!");
        if (o is string)
            Console.WriteLine("str!");
    }
}

Current codegen:

; Method Prog:Foo(System.Object):this
G_M20911_IG01:              ;; offset=0000H
       57                   push     rdi
       56                   push     rsi
       4883EC28             sub      rsp, 40
       488BF2               mov      rsi, rdx
       33FF                 xor      edi, edi
;; ========= loop start =========
G_M20911_IG03:              
       488BCE               mov      rcx, rsi
       4885C9               test     rcx, rcx
       741F                 je       SHORT G_M20911_IG06
       48B830A9B604F97F0000 mov      rax, 0x7FF904B6A930      ; System.String
       483901               cmp      qword ptr [rcx], rax
       7510                 jne      SHORT G_M20911_IG06
       48B9C09530808C020000 mov      rcx, 0x28C803095C0      ; 'str!'
       FF1576C79000         call     [System.Console:WriteLine(System.String)]
G_M20911_IG06:              
       488BCE               mov      rcx, rsi
       4885C9               test     rcx, rcx
       741F                 je       SHORT G_M20911_IG09
       48B830A9B604F97F0000 mov      rax, 0x7FF904B6A930      ; System.String
       483901               cmp      qword ptr [rcx], rax
       7510                 jne      SHORT G_M20911_IG09
       48B9C09530808C020000 mov      rcx, 0x28C803095C0      ; 'str!'
       FF154FC79000         call     [System.Console:WriteLine(System.String)]
G_M20911_IG09:              
       FFC7                 inc      edi
       83FF64               cmp      edi, 100
       7CAB                 jl       SHORT G_M20911_IG03
;; ========= loop end ===========
       4883C428             add      rsp, 40
       5E                   pop      rsi
       5F                   pop      rdi
       C3                   ret      
; Total bytes of code: 103

Due to early expansion, we don't hoist and don't perform CSE for it.
Expected codegen if we do the expansion in late phases:

; Method Prog:Foo(System.Object):this
G_M20911_IG01:              ;; offset=0000H
       57                   push     rdi
       56                   push     rsi
       53                   push     rbx
       4883EC20             sub      rsp, 32
       4885D2               test     rdx, rdx
       7413                 je       SHORT G_M20911_IG04
       48B930A934F6F87F0000 mov      rcx, 0x7FF8F634A930      ; System.String
       33C0                 xor      rax, rax
       48390A               cmp      qword ptr [rdx], rcx
       480F45D0             cmovne   rdx, rax
G_M20911_IG04:              ;; offset=001FH
       33F6                 xor      esi, esi
       4885D2               test     rdx, rdx
       400F95C6             setne    sil
       33FF                 xor      edi, edi
;; ========= loop start =========
G_M20911_IG05:              ;; offset=002AH
       85F6                 test     esi, esi
       741C                 je       SHORT G_M20911_IG07
       48BBC095200048020000 mov      rbx, 0x248002095C0      ; 'str!'
       488BCB               mov      rcx, rbx
       FF1567C79000         call     [System.Console:WriteLine(System.String)]
       488BCB               mov      rcx, rbx
       FF155EC79000         call     [System.Console:WriteLine(System.String)]
G_M20911_IG07:              ;; offset=004AH
       FFC7                 inc      edi
       83FF64               cmp      edi, 100
       7CD9                 jl       SHORT G_M20911_IG05
;; ========= loop end ===========
       4883C420             add      rsp, 32
       5B                   pop      rbx
       5E                   pop      rsi
       5F                   pop      rdi
       C3                   ret      
; Total bytes of code: 89

Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch, @kunalspathak
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Issue Details

---

void Foo(object o)
{
    for (int i = 0; i < 100; i++)
    {
        if (o is string)
            Console.WriteLine("str!");
        if (o is string)
            Console.WriteLine("str!");
    }
}

Current codegen:

; Method Prog:Foo(System.Object):this
G_M20911_IG01:              ;; offset=0000H
       57                   push     rdi
       56                   push     rsi
       4883EC28             sub      rsp, 40
       488BF2               mov      rsi, rdx
       33FF                 xor      edi, edi
;; ========= loop start =========
G_M20911_IG03:              
       488BCE               mov      rcx, rsi
       4885C9               test     rcx, rcx
       741F                 je       SHORT G_M20911_IG06
       48B830A9B604F97F0000 mov      rax, 0x7FF904B6A930      ; System.String
       483901               cmp      qword ptr [rcx], rax
       7510                 jne      SHORT G_M20911_IG06
       48B9C09530808C020000 mov      rcx, 0x28C803095C0      ; 'str!'
       FF1576C79000         call     [System.Console:WriteLine(System.String)]
G_M20911_IG06:              
       488BCE               mov      rcx, rsi
       4885C9               test     rcx, rcx
       741F                 je       SHORT G_M20911_IG09
       48B830A9B604F97F0000 mov      rax, 0x7FF904B6A930      ; System.String
       483901               cmp      qword ptr [rcx], rax
       7510                 jne      SHORT G_M20911_IG09
       48B9C09530808C020000 mov      rcx, 0x28C803095C0      ; 'str!'
       FF154FC79000         call     [System.Console:WriteLine(System.String)]
G_M20911_IG09:              
       FFC7                 inc      edi
       83FF64               cmp      edi, 100
       7CAB                 jl       SHORT G_M20911_IG03
;; ========= loop end ===========
       4883C428             add      rsp, 40
       5E                   pop      rsi
       5F                   pop      rdi
       C3                   ret      
; Total bytes of code: 103

Due to early expansion, we don't hoist and don't perform CSE for it.
Expected codegen if we do the expansion in late phases:

; Method Prog:Foo(System.Object):this
G_M20911_IG01:              ;; offset=0000H
       57                   push     rdi
       56                   push     rsi
       53                   push     rbx
       4883EC20             sub      rsp, 32
       4885D2               test     rdx, rdx
       7413                 je       SHORT G_M20911_IG04
       48B930A934F6F87F0000 mov      rcx, 0x7FF8F634A930      ; System.String
       33C0                 xor      rax, rax
       48390A               cmp      qword ptr [rdx], rcx
       480F45D0             cmovne   rdx, rax
G_M20911_IG04:              ;; offset=001FH
       33F6                 xor      esi, esi
       4885D2               test     rdx, rdx
       400F95C6             setne    sil
       33FF                 xor      edi, edi
;; ========= loop start =========
G_M20911_IG05:              ;; offset=002AH
       85F6                 test     esi, esi
       741C                 je       SHORT G_M20911_IG07
       48BBC095200048020000 mov      rbx, 0x248002095C0      ; 'str!'
       488BCB               mov      rcx, rbx
       FF1567C79000         call     [System.Console:WriteLine(System.String)]
       488BCB               mov      rcx, rbx
       FF155EC79000         call     [System.Console:WriteLine(System.String)]
G_M20911_IG07:              ;; offset=004AH
       FFC7                 inc      edi
       83FF64               cmp      edi, 100
       7CD9                 jl       SHORT G_M20911_IG05
;; ========= loop end ===========
       4883C420             add      rsp, 32
       5B                   pop      rbx
       5E                   pop      rsi
       5F                   pop      rdi
       C3                   ret      
; Total bytes of code: 89

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

[kunalspathak]

I think we have recently taken advantage of expanding nodes in late phase (e.g. #83911, #82973, #81635), wondering if we should have a top-level issue to revisit phases that should be expanded in late phase and have consolidated code to do this instead of having copies.