[llvm-bugs] [Bug 144861] [X86] bcmp with zero not vectorized

[LLVM Bugs via llvm-bugs]

Issue	144861
Summary	[X86] bcmp with zero not vectorized
Labels	backend:X86, missed-optimization
Assignees
Reporter	nikic

    A bcmp with an all zero value results in a sequence of ors, while a bcmp with all ones uses vptest.

https://llvm.godbolt.org/z/c15xY8nKv
```llvm
@zeroes = private unnamed_addr constant [64 x i8] zeroinitializer, align 1
@_ones_ = private unnamed_addr constant [64 x i8] c"\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF", align 1

declare i32 @bcmp(ptr, ptr, i64)

define zeroext i1 @test_zeroes(ptr %x) {
  %bcmp = tail call i32 @bcmp(ptr %x, ptr @zeroes, i64 64)
  %icmp = icmp eq i32 %bcmp, 0
  ret i1 %icmp
}

define zeroext i1 @test_ones(ptr %x) {
  %bcmp = tail call i32 @bcmp(ptr %x, ptr @ones, i64 64)
  %icmp = icmp eq i32 %bcmp, 0
  ret i1 %icmp
}
```

```
test_zeroes:                            # @test_zeroes
        mov     rax, qword ptr [rdi + 24]
        mov     rcx, qword ptr [rdi]
        mov     rdx, qword ptr [rdi + 8]
        mov rsi, qword ptr [rdi + 16]
        or      rsi, qword ptr [rdi + 48]
 or      rcx, qword ptr [rdi + 32]
        or      rcx, rsi
        or rax, qword ptr [rdi + 56]
        or      rdx, qword ptr [rdi + 40]
 or      rdx, rax
        or      rdx, rcx
        sete    al
 ret
test_ones:                              # @test_ones
        vmovdqu ymm0, ymmword ptr [rdi]
        vpand   ymm0, ymm0, ymmword ptr [rdi + 32]
 vpcmpeqd        ymm1, ymm1, ymm1
        vptest  ymm0, ymm1
 setb    al
        vzeroupper
        ret
```

The bcmp expansions look like this (https://llvm.godbolt.org/z/Tba34zYod):
```llvm
@zeroes = private unnamed_addr constant [64 x i8] zeroinitializer, align 1
@_ones_ = private unnamed_addr constant [64 x i8] c"\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF", align 1

define zeroext i1 @test_zeroes(ptr %x) {
start: 
  %0 = load i256, ptr %x, align 1
  %1 = getelementptr i8, ptr %x, i64 32
  %2 = load i256, ptr %1, align 1
  %3 = or i256 %0, %2
  %4 = icmp ne i256 %3, 0
  %5 = zext i1 %4 to i32
  %6 = icmp eq i32 %5, 0
  ret i1 %6
} 


define zeroext i1 @test_ones(ptr %x) {
start:
  %0 = load i256, ptr %x, align 1
 %1 = xor i256 %0, -1
  %2 = getelementptr i8, ptr %x, i64 32
  %3 = load i256, ptr %2, align 1
  %4 = xor i256 %3, -1
  %5 = or i256 %1, %4
  %6 = icmp ne i256 %5, 0
  %7 = zext i1 %6 to i32
  %8 = icmp eq i32 %7, 0
  ret i1 %8
}
```

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