[PATCH] D155457: [clang] Skip tautological comparison if the comparison involves the 'size_t' type

[Aaron Ballman via Phabricator via cfe-commits]

aaron.ballman added a comment.

In D155457#4511446 <https://reviews.llvm.org/D155457#4511446>, @xgupta wrote:

> In D155457#4511392 <https://reviews.llvm.org/D155457#4511392>, @aaron.ballman wrote:
>
>> Whether `size_t` comes from the system header or whether it's manually deduced from `decltype(sizeof(0))` should make no difference as far as the frontend is concerned; they should resolve to the same type. Can you explain the test failure you're seeing in a bit more detail?
>
>
>
>   : 'RUN: at line 1';   /home/shivam/.llvm/llvm-project/build/bin/clang -cc1 -internal-isystem /home/shivam/.llvm/llvm-project/build/lib/clang/17/include -nostdsysteminc /home/shivam/.llvm/llvm-project/clang/test/Sema/type-limit-compare.cpp -fsyntax-only -Wtautological-type-limit-compare -verify
>   --
>   Exit Code: 1
>   
>   Command Output (stderr):
>   --
>   error: 'warning' diagnostics seen but not expected: 
>     File /home/shivam/.llvm/llvm-project/clang/test/Sema/type-limit-compare.cpp Line 12: result of comparison 'uint64_t' (aka 'unsigned long long') > 18446744073709551615 is always false
>   1 error generated.
>
> I think the issue is with  (uint64_t)(____SIZE_MAX____) vs (uint64_t)std::numeric_limits<std::size_t>::max() but not sure.

Something seems odd to me about the current behavior. Consider: https://godbolt.org/z/ofezfhaPd

In the x86 compilation: `sizeof(std::size_t) < sizeof(uint64_t)` is true, so we test the other expression; because `Size` is greater than `__SIZE_MAX__` the function returns false and the second static assertion fails as expected.
In the x64 compilation: `sizeof(std::size_t) < sizeof(uint64_t)` is false (first static assertion fails) so we shouldn't even be evaluating the RHS of the `&&` to see if it's tautological because it can't contribute to the expression result, right?


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