Improve -Wparentheses for arbitrary bool contexts

[silvasean]

Bugzilla Link	34180
Version	unspecified
OS	Linux
CC	@m4tx,@zygoloid

Extended Description

https://godbolt.org/g/Ca2Xtv

bool f(int x) {
return x = 0;
}

GCC gives:

:2:16: warning: suggest parentheses around assignment used as truth value [-Wparentheses] return x = 0; ^

This would have caught a bug in r310794 (https://reviews.llvm.org/rL310794)

I don't know for sure, but from the reduced test case, it seems that GCC is just seeing when an assignment is used in a bool-typed context? E.g. just bool(x = 0) seems to trigger it. https://godbolt.org/g/HyBZHM
Looking at the two examples, it looks like ImplicitCastExpr to bool is probably the thing to look for.
ImplicitCastExpr 0x4fce318 <col:12, col:16> '_Bool'
ImplicitCastExpr 0x4fce578 <col:17, col:21> '_Bool'

[silvasean]

assigned to @m4tx

[silvasean]

Marking this as a beginner bug since it doesn't seem too difficult, though I haven't looked at the details inside clang.

[llvmbot]

a tentative fix is available at https://reviews.llvm.org/D45401

[llvmbot]

Hi!

This issue may be a good introductory issue for people new to working on LLVM. If you would like to work on this issue, your first steps are:

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2. Fix the issue locally.
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4. Create a git commit
5. Run git clang-format HEAD~1 to format your changes.
6. Submit the patch to Phabricator.
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[Endilll]

@m4tx are you still working on this?

[m4tx]

No, this can be reassigned.

[Endilll]

Still reproducible as of post-17 trunk: https://gcc.godbolt.org/z/4re8xjYcf

[seranu]

Hi there, I'm new to LLVM/clang and would like to work on this issue. Could you please assign it to me?