[llvm-bugs] [Bug 45863] New: __restrict on struct member has no effect

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https://bugs.llvm.org/show_bug.cgi?id=45863

            Bug ID: 45863
           Summary: __restrict on struct member has no effect
           Product: clang
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: C++
          Assignee: unassignedclangbugs at nondot.org
          Reporter: dsharlet at google.com
                CC: blitzrakete at gmail.com, dgregor at apple.com,
                    erik.pilkington at gmail.com, llvm-bugs at lists.llvm.org,
                    richard-llvm at metafoo.co.uk

The following code demonstrates the issue:

const int N = 8;

void add1(const float* __restrict a, const float* __restrict b, float*
__restrict c) {
  for (int i = 0; i < N; i++) {
    c[i] = a[i] + b[i];
  }
}

struct A {
  float * __restrict x;
};

void add2(const A& a, const A& b, A& c) {
  for (int i = 0; i < N; i++) {
    c.x[i] = a.x[i] + b.x[i];
  }
}

When compiling this with clang -S -O2 -march=native, I see a vectorized loop
for add1, but not for add2. When I look at the generated LLVM assembly, there's
no indication that the noalias attribute was applied to any of the pointers.
Adding __restrict to the function argument references does not help either (but
I wouldn't expect it to).

As far as I can tell, this is supposed to work to indicate that none of the x
pointers in add2 alias, at least in C.

I just tried this on a recently updated trunk Clang+LLVM and see the same
behavior (commit 57fb56b30e8).

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