[llvm-bugs] [Bug 38242] New: Missed chance for auto vectorization

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=38242

            Bug ID: 38242
           Summary: Missed chance for auto vectorization
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Loop Optimizer
          Assignee: unassignedbugs at nondot.org
          Reporter: david.bolvansky at gmail.com
                CC: llvm-bugs at lists.llvm.org

Code:
typedef struct {
    int *arr;
    unsigned size;
} attr_t;

int foo(attr_t *e, int x) {
    int s = e->size;
    for (unsigned i = 0; i < s; ++i) {
        e->arr[i] = i + x;
    }
};

Clang -O3
foo(attr_t*, int):                        
        mov     rax, qword ptr [rdi]
        xor     ecx, ecx
.LBB0_1:                               
        lea     edx, [rsi + rcx]
        mov     edi, ecx
        mov     dword ptr [rax + 4*rdi], edx
        add     ecx, 1
        jmp     .LBB0_1

GCC can vectorize it well.

Godbolt: 
https://godbolt.org/g/ytE3UW

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