This patch adds a new __builtin_assume_dereferenceable to encode
dereferenceability of a pointer using llvm.assume with an operand
bundle.
For now the builtin only accepts constant sizes, I am planning to drop
this restriction in a follow-up change.
This can be used to better optimize cases where a pointer is known to be
dereferenceable, e.g. unconditionally loading from p2 when vectorizing
the loop.
int *get_ptr();
void foo(int* src, int x) {
int *p2 = get_ptr();
__builtin_assume_aligned(p2, 4);
__builtin_assume_dereferenceable(p2, 4000);
for (unsigned I = 0; I != 1000; ++I) {
int x = src[I];
if (x == 0)
x = p2[I];
src[I] = x;
}
}
PR: https://github.com/llvm/llvm-project/pull/121789
50d10b5c1c