[Bug tree-optimization/119294] New: Strange (buggy?) codegen when passing cleared vector as argument

[gcc at haasn dot dev via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119294

            Bug ID: 119294
           Summary: Strange (buggy?) codegen when passing cleared vector
                    as argument
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gcc at haasn dot dev
  Target Milestone: ---

### Description

For some reason, in this program, GCC extraneously writes the vector argument,
normally passed in xmm0, to the stack - sometimes without even incrementing
the stack pointer.

It's furthermore strange that `set_indirect()` compiles to different code than
`set()`, even though the former (should) just directly inline the latter.

You can see that the problem goes away when the value to write is a compile
time constant, rather than taken from a register argument.

### Code

typedef char vec_t __attribute__((vector_size(16)));

void func(vec_t x);

void set(vec_t x, const char val)
{
    for (int i = 0; i < 16; i++)
        x[i] = val;

    func(x);
}

void set_indirect(vec_t x, const char val)
{
    set(x, val);
}

void setFF(vec_t x)
{
    set(x, 0xFF);
}

void set123(vec_t x)
{
    set(x, 123);
}

void set0(vec_t x)
{
    set(x, 0);
}

### Expected Output

set:
        vmovd   xmm0, edi
        vpbroadcastb    xmm0, xmm0
        jmp     func@PLT

set_indirect:
        vmovd   xmm0, edi
        vpbroadcastb    xmm0, xmm0
        jmp     func@PLT

setFF:
        vpcmpeqd        xmm0, xmm0, xmm0
        jmp     func@PLT

.LCPI3_1:
        .zero   4,123
set123:
        vbroadcastss    xmm0, dword ptr [rip + .LCPI3_1]
        jmp     func@PLT

set0:
        vxorps  xmm0, xmm0, xmm0
        jmp     func@PLT

### Actual Output

set:
        vmovd   xmm0, edi
        sub     rsp, 24
        vpbroadcastb    xmm0, xmm0
        vmovdqa XMMWORD PTR [rsp], xmm0
        call    func
        add     rsp, 24
        ret
set_indirect:
        vmovd   xmm0, edi
        vpbroadcastb    xmm0, xmm0
        vmovdqa XMMWORD PTR [rsp-24], xmm0
        jmp     func
setFF:
        vpcmpeqd        xmm0, xmm0, xmm0
        jmp     func
set123:
        mov     eax, 2071690107
        vmovd   xmm0, eax
        vpbroadcastd    xmm0, xmm0
        jmp     func
set0:
        vpxor   xmm0, xmm0, xmm0
        jmp     func

### See Also:

https://godbolt.org/z/1hrjKqf8Y