This patch adds a simplification if an OR weakens the overflow condition

for umul.with.overflow by treating any non-zero result as overflow. In that

case, we overflow if both umul.with.overflow operands are != 0, as in that

case the result can only be 0, iff the multiplication overflows.

Code like this is generated by code using __builtin_mul_overflow with

negative integer constants, e.g.

bool test(unsigned long long v, unsigned long long *res) { return __builtin_mul_overflow(v, -4775807LL, res); }

This simplification is very specific and I am not sure if visitOr is the

best place for it. Any other suggestions?

---------------------------------------- Name: D74141 %res = umul_overflow {i8, i1} %a, %b %mul = extractvalue {i8, i1} %res, 0 %overflow = extractvalue {i8, i1} %res, 1 %cmp = icmp ne %mul, 0 %ret = or i1 %overflow, %cmp ret i1 %ret => %t0 = icmp ne i8 %a, 0 %t1 = icmp ne i8 %b, 0 %ret = and i1 %t0, %t1 ret i1 %ret %res = umul_overflow {i8, i1} %a, %b %mul = extractvalue {i8, i1} %res, 0 %cmp = icmp ne %mul, 0 %overflow = extractvalue {i8, i1} %res, 1 Done: 1 Optimization is correct!