[webkit-dev] Unused parameter warnings / errors / warning fixes

Geoffrey Garen ggaren at apple.com
Mon Jan 26 11:31:24 PST 2015

> And I do agree that it can be inconvenient to deal with these warnings in heavily #ifdef’d code. I think there are some good strategies for avoiding that, and I’d like to talk about specific irritating cases so I can propose the strategy I’d push for. Generally the strategy is to push more configuration specifics to the edges rather than spreading them through multiple functions.

A few irritating cases for me:


static inline void validate(const Range& range)
    BeginTag* beginTag = LargeChunk::beginTag(range.begin());
    EndTag* endTag = LargeChunk::endTag(range.begin(), range.size());

    BASSERT(range.size() >= largeMin);
    BASSERT(beginTag->size() == range.size());

    BASSERT(beginTag->size() == endTag->size());
    BASSERT(beginTag->isFree() == endTag->isFree());
    BASSERT(beginTag->hasPhysicalPages() == endTag->hasPhysicalPages());
    BASSERT(static_cast<BoundaryTag*>(endTag) == static_cast<BoundaryTag*>(beginTag) || endTag->isEnd());


inline void vmValidate(size_t vmSize)
    // We use getpagesize() here instead of vmPageSize because vmPageSize is
    // allowed to be larger than the OS's true page size.

    BASSERT(vmSize == roundUpToMultipleOf(static_cast<size_t>(getpagesize()), vmSize));


inline void vmValidate(void* p, size_t vmSize)
    // We use getpagesize() here instead of vmPageSize because vmPageSize is
    // allowed to be larger than the OS's true page size.

    BASSERT(p == mask(p, ~(getpagesize() - 1)));

The common theme in these cases is that I wanted to write a helper function to do some ASSERTs which compiled to nothing in a release build. Compiling the function to nothing made its parameters look like errors.

I considered having the validate function return a value, and having the caller ASSERT(validate(x)) — that way, the call would compile to nothing, and the callee would always appear to do something with its parameters. I didn’t like that solution for two reasons:

(1) When debugging or reading a crash report, I wanted the indicated line of code to be the specific condition that failed. If the caller ASSERTs after a long line of reasoning, the indicated line of code is the non-specific ASSERT in the caller. This was a big deal to me.

(2) In cases where one validate needed to call another, I sometimes still had an unused parameter in the caller.

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