!struct.x && !struct.y produces worse code than (struct.x == 0) && (struct.y == 0)

[Kmeakin]

!it.x && !it.y produces worse code than (it.x == 0) && (it.y == 0) if it is a struct type with bool members x and y.

Oddly using a uint8_t for x and y does not suffer from this problem.

This affects AArch64, x86-64 and RiscV targets

Real-world motivation

This struct from mimalloc

// The `in_full` and `has_aligned` page flags are put in a union to efficiently
// test if both are false (`full_aligned == 0`) in the `mi_free` routine.
typedef union mi_page_flags_s {
  uint8_t full_aligned;
  struct {
    uint8_t in_full : 1;
    uint8_t has_aligned : 1;
  } x;
} mi_page_flags_t;

C++ code

https://godbolt.org/z/1387M789s

#include <cstdint>

struct S1 {
    bool x;
    bool y;
};

struct S2 {
    bool x : 1;
    bool y : 1;
};

struct S3 {
    uint8_t x : 1;
    uint8_t y : 1;
};

struct S4 {
    uint8_t x ;
    uint8_t y ;
};

extern "C" {
auto src1(S1 it) -> bool { return !it.x && !it.y; }
auto tgt1(S1 it) -> bool { return (it.x == 0) && (it.y == 0); }

auto src2(S2 it) -> bool { return !it.x && !it.y; }
auto tgt2(S2 it) -> bool { return (it.x == 0) && (it.y == 0); }

auto src3(S3 it) -> bool { return !it.x && !it.y; }
auto tgt3(S3 it) -> bool { return (it.x == 0) && (it.y == 0); }

auto src4(S4 it) -> bool { return !it.x && !it.y; }
auto tgt4(S4 it) -> bool { return (it.x == 0) && (it.y == 0); }
}

AArch64 assembly

src1:
        tst     x0, #0x100
        eor     w9, w0, #0x1
        cset    w8, eq
        and     w0, w8, w9
        ret

tgt1:
        mov     w8, #257
        tst     x0, x8
        cset    w0, eq
        ret

src2:
        tst     x0, #0x2
        eor     w9, w0, #0x1
        cset    w8, eq
        and     w0, w8, w9
        ret

tgt2:
        tst     x0, #0x3
        cset    w0, eq
        ret

src3:
        tst     x0, #0x3
        cset    w0, eq
        ret

tgt3:
        tst     x0, #0x3
        cset    w0, eq
        ret

src4:
        tst     x0, #0xffff
        cset    w0, eq
        ret

tgt4:
        tst     x0, #0xffff
        cset    w0, eq
        ret

Alive proof

https://alive2.llvm.org/ce/z/JRwXu7

----------------------------------------
define i1 @src1(i64 %#0) nofree willreturn memory(none) {
#1:
  %#2 = trunc i64 %#0 to i1
  %#3 = and i64 %#0, 256
  %#4 = icmp eq i64 %#3, 0
  %#5 = xor i1 %#2, 1
  %#6 = and i1 %#4, %#5
  ret i1 %#6
}
=>
define i1 @tgt1(i64 %#0) nofree willreturn memory(none) {
#1:
  %#2 = and i64 %#0, 257
  %#3 = icmp eq i64 %#2, 0
  ret i1 %#3
}
Transformation seems to be correct!


----------------------------------------
define i1 @src2(i64 %#0) nofree willreturn memory(none) {
#1:
  %#2 = trunc i64 %#0 to i1
  %#3 = and i64 %#0, 2
  %#4 = icmp eq i64 %#3, 0
  %#5 = xor i1 %#2, 1
  %#6 = and i1 %#4, %#5
  ret i1 %#6
}
=>
define i1 @tgt2(i64 %#0) nofree willreturn memory(none) {
#1:
  %#2 = and i64 %#0, 3
  %#3 = icmp eq i64 %#2, 0
  ret i1 %#3
}
Transformation seems to be correct!


----------------------------------------
define i1 @src3(i64 %#0) nofree willreturn memory(none) {
#1:
  %#2 = and i64 %#0, 3
  %#3 = icmp eq i64 %#2, 0
  ret i1 %#3
}
=>
define i1 @tgt3(i64 %#0) nofree willreturn memory(none) {
#1:
  %#2 = and i64 %#0, 3
  %#3 = icmp eq i64 %#2, 0
  ret i1 %#3
}
Transformation seems to be correct!


----------------------------------------
define i1 @src4(i64 %#0) nofree willreturn memory(none) {
#1:
  %#2 = and i64 %#0, 65535
  %#3 = icmp eq i64 %#2, 0
  ret i1 %#3
}
=>
define i1 @tgt4(i64 %#0) nofree willreturn memory(none) {
#1:
  %#2 = and i64 %#0, 65535
  %#3 = icmp eq i64 %#2, 0
  ret i1 %#3
}
Transformation seems to be correct!

Summary:
  4 correct transformations
  0 incorrect transformations
  0 failed-to-prove transformations
  0 Alive2 errors

[llvmbot]

@llvm/issue-subscribers-backend-aarch64

Author: Karl Meakin (Kmeakin)

`!it.x && !it.y` produces worse code than `(it.x == 0) && (it.y == 0)` if `it` is a struct type with `bool` members `x` and `y`.

Oddly using a uint8_t for x and y does not suffer from this problem.

Real-world motivation

This struct from mimalloc

// The `in_full` and `has_aligned` page flags are put in a union to efficiently
// test if both are false (`full_aligned == 0`) in the `mi_free` routine.
typedef union mi_page_flags_s {
  uint8_t full_aligned;
  struct {
    uint8_t in_full : 1;
    uint8_t has_aligned : 1;
  } x;
} mi_page_flags_t;

C++ code

https://godbolt.org/z/1387M789s

#include <cstdint>

struct S1 {
    bool x;
    bool y;
};

struct S2 {
    bool x : 1;
    bool y : 1;
};

struct S3 {
    uint8_t x : 1;
    uint8_t y : 1;
};

struct S4 {
    uint8_t x ;
    uint8_t y ;
};

extern "C" {
auto src1(S1 it) -> bool { return !it.x && !it.y; }
auto tgt1(S1 it) -> bool { return (it.x == 0) && (it.y == 0); }

auto src2(S2 it) -> bool { return !it.x && !it.y; }
auto tgt2(S2 it) -> bool { return (it.x == 0) && (it.y == 0); }

auto src3(S3 it) -> bool { return !it.x && !it.y; }
auto tgt3(S3 it) -> bool { return (it.x == 0) && (it.y == 0); }

auto src4(S4 it) -> bool { return !it.x && !it.y; }
auto tgt4(S4 it) -> bool { return (it.x == 0) && (it.y == 0); }
}

AArch64 assembly

src1:
        tst     x0, #<!-- -->0x100
        eor     w9, w0, #<!-- -->0x1
        cset    w8, eq
        and     w0, w8, w9
        ret

tgt1:
        mov     w8, #<!-- -->257
        tst     x0, x8
        cset    w0, eq
        ret

src2:
        tst     x0, #<!-- -->0x2
        eor     w9, w0, #<!-- -->0x1
        cset    w8, eq
        and     w0, w8, w9
        ret

tgt2:
        tst     x0, #<!-- -->0x3
        cset    w0, eq
        ret

src3:
        tst     x0, #<!-- -->0x3
        cset    w0, eq
        ret

tgt3:
        tst     x0, #<!-- -->0x3
        cset    w0, eq
        ret

src4:
        tst     x0, #<!-- -->0xffff
        cset    w0, eq
        ret

tgt4:
        tst     x0, #<!-- -->0xffff
        cset    w0, eq
        ret

Alive proof

https://alive2.llvm.org/ce/z/JRwXu7

----------------------------------------
define i1 @<!-- -->src1(i64 %#<!-- -->0) nofree willreturn memory(none) {
#<!-- -->1:
  %#<!-- -->2 = trunc i64 %#<!-- -->0 to i1
  %#<!-- -->3 = and i64 %#<!-- -->0, 256
  %#<!-- -->4 = icmp eq i64 %#<!-- -->3, 0
  %#<!-- -->5 = xor i1 %#<!-- -->2, 1
  %#<!-- -->6 = and i1 %#<!-- -->4, %#<!-- -->5
  ret i1 %#<!-- -->6
}
=&gt;
define i1 @<!-- -->tgt1(i64 %#<!-- -->0) nofree willreturn memory(none) {
#<!-- -->1:
  %#<!-- -->2 = and i64 %#<!-- -->0, 257
  %#<!-- -->3 = icmp eq i64 %#<!-- -->2, 0
  ret i1 %#<!-- -->3
}
Transformation seems to be correct!


----------------------------------------
define i1 @<!-- -->src2(i64 %#<!-- -->0) nofree willreturn memory(none) {
#<!-- -->1:
  %#<!-- -->2 = trunc i64 %#<!-- -->0 to i1
  %#<!-- -->3 = and i64 %#<!-- -->0, 2
  %#<!-- -->4 = icmp eq i64 %#<!-- -->3, 0
  %#<!-- -->5 = xor i1 %#<!-- -->2, 1
  %#<!-- -->6 = and i1 %#<!-- -->4, %#<!-- -->5
  ret i1 %#<!-- -->6
}
=&gt;
define i1 @<!-- -->tgt2(i64 %#<!-- -->0) nofree willreturn memory(none) {
#<!-- -->1:
  %#<!-- -->2 = and i64 %#<!-- -->0, 3
  %#<!-- -->3 = icmp eq i64 %#<!-- -->2, 0
  ret i1 %#<!-- -->3
}
Transformation seems to be correct!


----------------------------------------
define i1 @<!-- -->src3(i64 %#<!-- -->0) nofree willreturn memory(none) {
#<!-- -->1:
  %#<!-- -->2 = and i64 %#<!-- -->0, 3
  %#<!-- -->3 = icmp eq i64 %#<!-- -->2, 0
  ret i1 %#<!-- -->3
}
=&gt;
define i1 @<!-- -->tgt3(i64 %#<!-- -->0) nofree willreturn memory(none) {
#<!-- -->1:
  %#<!-- -->2 = and i64 %#<!-- -->0, 3
  %#<!-- -->3 = icmp eq i64 %#<!-- -->2, 0
  ret i1 %#<!-- -->3
}
Transformation seems to be correct!


----------------------------------------
define i1 @<!-- -->src4(i64 %#<!-- -->0) nofree willreturn memory(none) {
#<!-- -->1:
  %#<!-- -->2 = and i64 %#<!-- -->0, 65535
  %#<!-- -->3 = icmp eq i64 %#<!-- -->2, 0
  ret i1 %#<!-- -->3
}
=&gt;
define i1 @<!-- -->tgt4(i64 %#<!-- -->0) nofree willreturn memory(none) {
#<!-- -->1:
  %#<!-- -->2 = and i64 %#<!-- -->0, 65535
  %#<!-- -->3 = icmp eq i64 %#<!-- -->2, 0
  ret i1 %#<!-- -->3
}
Transformation seems to be correct!

Summary:
  4 correct transformations
  0 incorrect transformations
  0 failed-to-prove transformations
  0 Alive2 errors

[dtcxzyw]

cc @andjo403

[andjo403]

this is the continuation of #122179 I have the code prepared but still needs test and as I understand it there is some regressions also that is the reason that I have not finished the tests