JIT: missing opportunity for Redundant Branch Opt

[EgorBo]

A simplified repro of what I saw in a real code:

void Test(int a)
{
    if (a >= 100)
    {
        if (a <= 100)
        {
            Console.WriteLine(a);
        }
    }
}

Current codegen:

; Method Prog:Test(int):this (FullOpts)
G_M36082_IG01:
       sub      rsp, 40
G_M36082_IG02:
       cmp      edx, 100
       jl       SHORT G_M36082_IG04
G_M36082_IG03:
       cmp      edx, 100
       jg       SHORT G_M36082_IG04
       mov      ecx, edx
       call     [System.Console:WriteLine(int)]
G_M36082_IG04:
       nop      
G_M36082_IG05:
       add      rsp, 40
       ret      
; Total bytes of code: 28

Expected codegen:

; Method Prog:Test(int):this (FullOpts)
G_M36082_IG01:
       sub      rsp, 40
G_M36082_IG02:
       cmp      edx, 100
       jne      SHORT G_M36082_IG04
G_M36082_IG03:
       mov      ecx, 100
       call     [System.Console:WriteLine(int)]
G_M36082_IG04:
       nop      
G_M36082_IG05:
       add      rsp, 40
       ret      
; Total bytes of code: 26

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Issue Details

---

A simplified repro of what I saw in a real code:

void Test(int a)
{
    if (a >= 100)
    {
        if (a <= 100)
        {
            Console.WriteLine(a);
        }
    }
}

Current codegen:

; Method Prog:Test(int):this (FullOpts)
G_M36082_IG01:
       sub      rsp, 40
G_M36082_IG02:
       cmp      edx, 100
       jl       SHORT G_M36082_IG04
G_M36082_IG03:
       cmp      edx, 100
       jg       SHORT G_M36082_IG04
       mov      ecx, edx
       call     [System.Console:WriteLine(int)]
G_M36082_IG04:
       nop      
G_M36082_IG05:
       add      rsp, 40
       ret      
; Total bytes of code: 28

Expected codegen:

; Method Prog:Test(int):this (FullOpts)
G_M36082_IG01:
       sub      rsp, 40
G_M36082_IG02:
       cmp      edx, 100
       jne      SHORT G_M36082_IG04
G_M36082_IG03:
       mov      ecx, 100
       call     [System.Console:WriteLine(int)]
G_M36082_IG04:
       nop      
G_M36082_IG05:
       add      rsp, 40
       ret      
; Total bytes of code: 26

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

[EgorBo]

сс @AndyAyersMS I assume this is slightly different from "implied relops" opts we have.
In this case we can:

1. Change the 2nd condition to just == 100 (and then assertprop can propagate it as a constant)
2. Ideally change the dominating comparison if there are no statements between two?

[AndyAyersMS]

Looks similar to the case noted in #81220 (comment).

Linked this example into #48115.