void added a reviewer: rsmith.
void added a subscriber: rsmith.
void added a comment.

@rsmith, @serge-sans-paille, and @kees, I need some advice. There's a test in 
`clang/test/CodeGen/bounds-checking.c` that's checking bounds stuff on unions. 
The behavior is...weird to me. It says that an array of 0 or 1 is a FAM, but 
one larger is not (see below). That seems counter to how structs are handled. 
If this is true, then the check in `clang/lib/AST/Expr.cpp` also needs to be 
updated...

  union U { int a[0]; int b[1]; int c[2]; };                                    
         
    
  // CHECK-LABEL: define {{.*}} @f4                                             
         
  int f4(union U *u, int i) {
    // a and b are treated as flexible array members.
    // CHECK-NOT: @llvm.ubsantrap                                               
         
    return u->a[i] + u->b[i] + u->c[i];                                         
         
    // CHECK: }
  }                                                                             
         
    
  // CHECK-LABEL: define {{.*}} @f5
  int f5(union U *u, int i) {
    // c is not a flexible array member.
    // NONLOCAL: call {{.*}} @llvm.ubsantrap                                    
         
    return u->c[i];
    // CHECK: }                                                                 
         
  }   


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D134902/new/

https://reviews.llvm.org/D134902

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