Delegates are poorly inlined and optimized

[deeprobin]

C# Code

Example without using delegate

    public int AddFunc(int a, int b) {
        return a + b;
    }

Example with delegate

    public int DelegateFunc(int a, int b) {
        Func<int, int, int> e = delegate(int c, int d) {
            return a + b;
        };
        return e(a, b);
    }

Analysis

See [sharplab example](https://sharplab.io/#v2:EYLgxg9gTgpgtADwGwBYA0AXEBDAzgWwB8ABAJgEYBYAKGIGYACMhgYQYG8aHunGBLAHYYGAQQAmY4gFYAFIOHY0DeQ2ABKDlx7biAdgbYGAalUBuLdwC+FhjfrKhDACIwANjADm2DDGlzHig7C6prU2jpSADzySjFBAHwMMAwAvAxibp7eMP7CYLGOYhqcYeFlegbGZjbalual5fo5ger1tTSWQA===

Stopwatch benchmark without Benchmark.NET

On the one hand, of course, all the code to instantiate a delegate function is created, however, the actual code executed is also very poorly optimized.

Assembly result

AddFunc

    L0000: lea eax, [rdx+r8]
    L0004: ret

Content of Func<int, int, int>

    L0000: mov eax, [rcx+8]
    L0003: add eax, [rcx+0xc]
    L0006: ret

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Issue Details

---

C# Code

Example without using delegate

    public int AddFunc(int a, int b) {
        return a + b;
    }

Example with delegate

    public int DelegateFunc(int a, int b) {
        Func<int, int, int> e = delegate(int c, int d) {
            return a + b;
        };
        return e(a, b);
    }

Analysis

See [sharplab example](https://sharplab.io/#v2:EYLgxg9gTgpgtADwGwBYA0AXEBDAzgWwB8ABAJgEYBYAKGIGYACMhgYQYG8aHunGBLAHYYGAQQAmY4gFYAFIOHY0DeQ2ABKDlx7biAdgbYGAalUBuLdwC+FhjfrKhDACIwANjADm2DDGlzHig7C6prU2jpSADzySjFBAHwMMAwAvAxibp7eMP7CYLGOYhqcYeFlegbGZjbalual5fo5ger1tTSWQA===

Stopwatch benchmark without Benchmark.NET

On the one hand, of course, all the code to instantiate a delegate function is created, however, the actual code executed is also very poorly optimized.

Assembly result

AddFunc

    L0000: lea eax, [rdx+r8]
    L0004: ret

Content of Func<int, int, int>

    L0000: mov eax, [rcx+8]
    L0003: add eax, [rcx+0xc]
    L0006: ret

Author:	deeprobin
Assignees:	-
Labels:	tenet-performance, area-CodeGen-coreclr, untriaged
Milestone:	-

[stephentoub]

Dup of #56708, #6498, #4584, ...

[deeprobin]

@stephentoub Super. Thanks I have probably overlooked.