Hi Qing, Just looking at a very high level, I have a few comments:
1. Constant folding str(n)cmp - folding is done separately in fold-const-call.c and gimple-fold.c. There is already code for folding strcmp and strncmp, so we shouldn't need to add new foldings. Or do you have an example that isn't folded as expected? If so, a fix should be added to the existing code. 2. Why check for str(n)cmp == 0 / != 0? There is no need to explicitly check for equality comparisons since folding into memcmp is always good. 3. Why handle strncmp? There is already code to convert strncmp into strcmp, so why repeat that again in a different way? It just seems to make the code significantly more complex for no benefit. You can achieve the same effect by just optimizing strcmp into memcmp when legal without checking for equality comparison. As a result you can considerably reduce the size of this patch while handling more useful cases. Wilco
