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Are you sure this is an alias problem? What is happening is LLVM is leaving the code looking like this: int foo(int *p, volatile int *q, int n) { int i, s = 0; for (i = 0; i < n; ++i) s += *p + *q; return s; } but GCC is changing to code to look like this: int foo(int *p, volatile int *q, int n) { int i, s = 0; int t; t = *p; for (i = 0; i < n; ++i) s += t + *q;

A customer has reported a performance problem, which I have eventually tracked down to the following situation: Consider this program: int foo(int *p, volatile int *q, int n) { int i, s = 0; for (i = 0; i < n; ++i) s += *p + *q; return s; } LLVM's analysis indicates that *p and *q can alias, even though *p is non-volatile whereas *q is volatile. I don't have the