[cfe-dev] CFG Terminator Conditions

[Gábor Horváth via cfe-dev]

Hi!

I found the terminator condition for binary operators a bit unintuitive in
the CFG. I was wondering if I am missing something or it is a possible
improvement.

Let's consider the following simple code snippet:

void g(bool a, bool b) {
    if (a || b) {
        body();
    } else {
        body2();
    }
}

We get the following CFG:

 [B1]
   1: body2
   2: [B1.1] (ImplicitCastExpr, FunctionToPointerDecay, void (*)(void))
   3: [B1.2]()
   Preds (1): B3
   Succs (1): B0

 [B2]
   1: body
   2: [B2.1] (ImplicitCastExpr, FunctionToPointerDecay, void (*)(void))
   3: [B2.2]()
   Preds (2): B3 B4
   Succs (1): B0

 [B3]
   1: b
   2: [B3.1] (ImplicitCastExpr, LValueToRValue, _Bool)
   T: if [B4.2] || [B3.2]
   Preds (1): B4
   Succs (2): B2 B1

 [B4]
   1: a
   2: [B4.1] (ImplicitCastExpr, LValueToRValue, _Bool)
   T: [B4.2] || ...
   Preds (1): B5
   Succs (2): B2 B3

The terminator condition for [B4] is (a cast above) a. This is pretty
intuitive. This value will determine which branch do we take when we leave
the basic block.

The terminator condition for [B3], however, is the whole binary or
expression. I would expect it to be the right hand side of the logical or.
What do you think? What is the reason that we have the whole expression
here?

Regards,
Gabor
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/cfe-dev/attachments/20180803/6b6feb31/attachment.html>