Improve morphing of bit comparisons to constant 0/1

[dubiousconst282]

This PR does the following:

• Allow morphing ((x >> CNS(y)) & 1) EQ/NE 0/1 -> (x & CNS(1 << y)) EQ/NE 0 with non-constant y, but only in some cases (if it's comparing the result to non-zero, or if the node is being used by a branch). This allows the lowering pass to create BT nodes for the latter pattern.
• Lower EQ(AND(x, 1), 1) into AND(x, 1) by checking for TEST_NE instead of EQ/NE nodes. This should remove the need to identify variations such as (x & 1) != 0, while also avoiding interferences with later transforms based on EQ/NE nodes.
• Lower NE/EQ(AND(x, 1), 0/1) into AND(x, 1)

I wasn't able to get the morph heuristic to work with (x >> y & 1) != 1, because the IR looks like EQ(EQ(..., 1), 0), but there are no diffs in this case.

Fixes #72986.

Diffs

    public static string BitTest_If_Ne0(int x, int y) => (x >> y & 1) != 0 ? "X" : " ";
    public static bool BitTest_Eq0(int x, int y) => (x >> y & 1) == 0;
    public static bool BitTest_Eq1(int x, int y) => (x >> y & 1) == 1;
    public static bool BitTest_Ne0(int x, int y) => (x >> y & 1) != 0;
    public static bool BitTest_Ne1(int x, int y) => (x >> y & 1) != 1;
    public static bool And1_Eq0(int x) => (x & 1) == 0;
    public static bool And1_Eq1(int x) => (x & 1) == 1;
    public static bool And1_Ne0(int x) => (x & 1) != 0;
    public static bool And1_Ne1(int x) => (x & 1) != 1;

 ; Assembly listing for method Program:BitTest_If_Ne0(int,int):System.String
-       sarx     eax, ecx, edx
-       test     al, 1
-       jne      SHORT G_M39616_IG05
+       bt       ecx, edx
+       jb       SHORT G_M39616_IG05
        mov      rax, 0xD1FFAB1E      ; " "
        mov      rax, gword ptr [rax]
        ret
        mov      rax, 0xD1FFAB1E      ; "X"
        mov      rax, gword ptr [rax]
        ret
 ; Assembly listing for method Program:BitTest_Eq0(int,int):bool
-       sarx     eax, ecx, edx
-       test     al, 1
-       sete     al
+       bt       ecx, edx
+       setae    al
        movzx    rax, al
        ret
 ; Assembly listing for method Program:BitTest_Eq1(int,int):bool
        sarx     eax, ecx, edx
        and      eax, 1
        ret
 ; Assembly listing for method Program:BitTest_Ne0(int,int):bool
        sarx     eax, ecx, edx
-       test     al, 1
-       setne    al
-       movzx    rax, al
+       and      eax, 1
        ret
 ; Assembly listing for method Program:BitTest_Ne1(int,int):bool
        sarx     eax, ecx, edx
        test     al, 1
        sete     al
        movzx    rax, al
        ret
 ; Assembly listing for method Program:And1_Eq0(int):bool
        xor      eax, eax
        test     cl, 1
        sete     al
        ret
 ; Assembly listing for method Program:And1_Eq1(int):bool
        mov      eax, ecx
        and      eax, 1
        ret
 ; Assembly listing for method Program:And1_Ne0(int):bool
-       xor      eax, eax
-       test     cl, 1
-       setne    al
+       mov      eax, ecx
+       and      eax, 1
        ret
 ; Assembly listing for method Program:And1_Ne1(int):bool
        xor      eax, eax
        test     cl, 1
        sete     al
        ret

SPMI diffs

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All CLA requirements met.

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Issue Details

---

This PR does the following:

• Allow morphing ((x >> CNS(y)) & 1) EQ/NE 0/1 -> (x & CNS(1 << y)) EQ/NE 0 with non-constant y. This allows the lowering pass to create BT nodes for the latter pattern.
• Lower EQ(AND(x, 1), 1) into AND(x, 1) by checking for TEST_NE instead of EQ/NE nodes. This should remove the need to identify variations such as (x & 1) != 0, while also avoiding interferences with later transforms based on EQ/NE nodes.

Fixes #72986.

Diffs

public static bool BitTest_Eq0(int x, int y) => (x >> y & 1) == 0;
public static bool BitTest_Eq1(int x, int y) => (x >> y & 1) == 1;
public static bool BitTest_Ne0(int x, int y) => (x >> y & 1) != 0;
public static bool BitTest_Ne1(int x, int y) => (x >> y & 1) != 1;
public static bool And1_Eq0(int x) => (x & 1) == 0;
public static bool And1_Eq1(int x) => (x & 1) == 1;
public static bool And1_Ne0(int x) => (x & 1) != 0;
public static bool And1_Ne1(int x) => (x & 1) != 1;

 ; Assembly listing for method Program:BitTest_Eq0(int,int):bool
-       8BC1                 mov      eax, ecx
-       8BCA                 mov      ecx, edx
-       D3F8                 sar      eax, cl
-       A801                 test     al, 1
-       0F94C0               sete     al
+       0FA3D1               bt       ecx, edx
+       0F93C0               setae    al
        0FB6C0               movzx    rax, al
        C3                   ret
 ; Assembly listing for method Program:BitTest_Eq1(int,int):bool
-       8BC1                 mov      eax, ecx
-       8BCA                 mov      ecx, edx
-       D3F8                 sar      eax, cl
-       83E001               and      eax, 1
+       0FA3D1               bt       ecx, edx
+       0F92C0               setb     al
+       0FB6C0               movzx    rax, al
        C3                   ret
 ; Assembly listing for method Program:BitTest_Ne0(int,int):bool
-       8BC1                 mov      eax, ecx
-       8BCA                 mov      ecx, edx
-       D3F8                 sar      eax, cl
-       A801                 test     al, 1
-       0F95C0               setne    al
+       0FA3D1               bt       ecx, edx
+       0F92C0               setb     al
        0FB6C0               movzx    rax, al
        C3                   ret
 ; Assembly listing for method Program:BitTest_Ne1(int,int):bool
-       8BC1                 mov      eax, ecx
-       8BCA                 mov      ecx, edx
-       D3F8                 sar      eax, cl
-       A801                 test     al, 1
-       0F94C0               sete     al
+       0FA3D1               bt       ecx, edx
+       0F93C0               setae    al
        0FB6C0               movzx    rax, al
        C3                   ret
 ; Assembly listing for method Program:And1_Eq0(int):bool
        33C0                 xor      eax, eax
        F6C101               test     cl, 1
        0F94C0               sete     al
        C3                   ret
 ; Assembly listing for method Program:And1_Eq1(int):bool
-       8BC1                 mov      eax, ecx
-       83E001               and      eax, 1
+       B801000000           mov      eax, 1
+       23C1                 and      eax, ecx
        C3                   ret
 ; Assembly listing for method Program:And1_Ne0(int):bool
-       33C0                 xor      eax, eax
-       F6C101               test     cl, 1
-       0F95C0               setne    al
+       B801000000           mov      eax, 1
+       23C1                 and      eax, ecx
        C3                   ret
 ; Assembly listing for method Program:And1_Ne1(int):bool
        33C0                 xor      eax, eax
        F6C101               test     cl, 1
        0F94C0               sete     al
        C3                   ret

Author:	dubiousconst282
Assignees:	-
Labels:	area-CodeGen-coreclr
Milestone:	-

[AndyAyersMS]

/azp run fuzzlyn

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[AndyAyersMS]

Changes LGTM. Thanks!

We will hold off on merging until the 7.0 release branches off from main (see #72297 for schedule).

[jakobbotsch]

The Fuzzlyn failures look like the ones fixed by #73146. I'm not really sure what happened here, normally jobs triggered via the bot run on a merge of the PR head commit and current main, but in this case it ran directly on the head commit 991ff69 that does not have c4ea81d.

I would retrigger it but since this is still a draft I'll wait.

[dubiousconst282]

Thanks! I was holding on draft to investigate regressions from the CI diffs, but there aren't many. I think it's ready now.

[AndyAyersMS]

@dubiousconst282 we are ready to take in new changes once more.

Can you fix the merge conflicts?

[dubiousconst282]

@AndyAyersMS Done

[AndyAyersMS]

/azp run fuzzlyn

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[AndyAyersMS]

Interesting and almost certainly unrelated Fuzzlyn failure. No core dump so not sure this is actionable.

FYI @janvorli in case we start seeing this more often.

OSX arm64 checked

Assert failure(PID 24175 [0x00005e6f], Thread: 2129739 [0x207f4b]): !"Unable to commit a loaderheap code page"
    File: /Users/runner/work/1/s/src/coreclr/utilcode/loaderheap.cpp Line: 1173
    Image: /private/tmp/helix/working/A4B6094A/p/CoreRoot/corerun

[AndyAyersMS]

@dubiousconst282 thank you for your contribution!