[cfe-dev] int-to-bool conversion issues

[Alexandre Isoard via cfe-dev]

Hello,

I encountered a really annoying issue, I am not sure it is Clang or C++
language issue.

But basically, the following code:

bool foo(bool a) {
return ~a;
}

Collapse into:

bool foo(bool a) {
return true;
}

The explanation is simple:
- a is implicitly converted to int using zext
- int operator~(int) has the unexpected behavior described below
- then icmp ne 0 is used to convert to bool and is always true

Here is the truth table of bool-to-int + operator~(int) + int-to-bool:
false → 0b0000 → 0b0000 → true
true → 0b0001 → 0b1110 → true

Note that we can solve the issue by using sext for bool-to-int conversions.
Should we? Is this a known problem?

-- 
*Alexandre Isoard*
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