Quuxplusone added inline comments.
================
Comment at: clang/lib/Sema/SemaChecking.cpp:7984
+ if (isa<IntegerLiteral>(ThirdArg) &&
+ cast<IntegerLiteral>(ThirdArg)->getValue() == 0) {
+ WarningKind = 0;
----------------
> Suppress the diagnostic in cases like `memset(ptr, 0xff, PADDING)`, when
> `PADDING` is a macro defined to be `0`.
Would it suffice to treat a literal `0xFF` in the exact same way you treat a
literal `0`? That is,
```
if (SecondArg is integer literal 0 or 255 || ThirdArg involves sizeof) {
do nothing
} else if (ThirdArg is integer literal 0 or 255 || SecondArg involves sizeof) {
diagnose it
}
```
You should add a test case proving that `memset(x, 0, 0)` doesn't get diagnosed
(assuming the two `0`s come from two different macro expansions, for example).
My sketch above would fail to diagnose `memset(x, 0, 255)`. I don't know if
this is a feature or a bug. :) You probably ought to have a test case for
that, either way, just to demonstrate the expected behavior.
https://reviews.llvm.org/D49112
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